UNIVERZITA PARDUBICE FAKULTA CHEMICKO-TECHNOLOGICKÁ ÚSTAV ORGANICKÉ CHEMIE A TECHNOLOGIE

D--A Chromophores with Nonlinear Optical Properties DISSERTATION

Author:

Daniel Cvejn

Supervisor:

Doc. Ing. Filip Bureš, Ph.D.

2015

Prohlašuji: Tuto práci jsem vypracoval samostatně. Veškeré literární prameny a informace, které jsem v práci využil, jsou uvedeny v seznamu použité literatury. Byl jsem seznámen s tím, že se na moji práci vztahují práva a povinnosti vyplývající ze zákona č. 121/2000 Sb., autorský zákon, zejména se skutečností, že Univerzita Pardubice má právo na uzavření licenční smlouvy o užití této práce jako školního díla podle § 60 odst. 1 autorského zákona, a s tím, že pokud dojde k užití této práce mnou nebo bude poskytnuta licence o užití jinému subjektu, je Univerzita Pardubice oprávněna ode mne požadovat přiměřený příspěvek na úhradu nákladů, které na vytvoření díla vynaložila, a to podle okolností až do jejich skutečné výše. Souhlasím s prezenčním zpřístupněním své práce v Univerzitní knihovně.

V Pardubicích dne 5.12.2015

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Dedicated to Mr. and Mrs. Eduard and Marie Cvejn. Věnováno manželům Eduardu a Marii Cvejnovým.

ACKNOWLEDGEMENT I would like to thank my supervisor, assoc. professor Filip Bureš, Ph. D., for all of the professional as well as personal support, (in my case necessary) patience and respect during my doctoral studies going far above and beyond his duty. Along with all of the collective of Bureš Group (Intstitute of Organic Chemistry and Technology, University of Pardubice) and all the co-authors of my publications, I would like to namely acknowledge these people (in surname alphabetical order) of my personal and/or professional life for all the personal support, help and/or nice and tight collaboration during my Ph. D. studies. Thank you all very much. Sylvain Achelle, Břetislav Brož, Jitka Cvejnová, Adéla Černá, Miloš Černý, Mihalis Fakis, Michaela Fecková, Jiří Fukala, Hana Hošnová, Iwan V. Kityk, Milan Klikar, Jana Kousalová, Klára Melánová, Petr Narwa, Patrik Pařík, Oldřich Pytela, Tomáš Ruffer, Martina Sebránková, Parmeshwar B. Solanke, Zdeněk Tomáš, Vítězslav Zima

Scientific outcomes of this work have been supported by the Czech Science Foundation (13-01061S) and the Technology Agency of the Czech Republic (TE01020022, Flexprint).

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ABSTRACT IN ENGLISH Three partially overlapping series of -conjugated push-pull chromophores, structurally related to triphenylamine, were synthesized to elucidate their fundamental structure-property relationships. The first two topics include triphenylamine-derived D--A systems for two-photon absorption; the third one involves model push-pull compounds capable of intercalation into layered inorganic hosts in order to get access to novel inorganicorganic hybrid materials with tailored properties. Target chromophores were prepared using modern cross-coupling reactions and their structure and properties were investigated by NMR, HR-MALDI-MS, IR spectroscopy, RTG analysis, electrochemistry, UV/Vis absorption/emission spectra, differential scanning calorimetry, two-photon excited fluorescent spectroscopy, second-harmonic generation and DFT calculations.

Keywords: Push-pull, triphenylamine, cross-coupling, nonlinear optics, two photon absorption, intercalation.

ABSTRACT IN CZECH Byly připraveny tři částečně se překrývající série -konjugovaných push-pull chromoforů, které jsou strukturně založeny na trifenylaminu, s cílem objasnit základní vztahy typu struktura-vlastnosti. První dva směry jsou reprezentovány D--A systémy na bázi trifenylaminu pro dvou fotonovou absorbci. Třetí oblast zahrnuje modelové push-pull sloučeniny schopné interkalace do vrstevnatého materiálu s cílem získat nový anorganickoorganický material s vylepšenými vlastnostmi. Cílové chromofory byly připraveny s využitím moderních cross-coupling reakcí a jejich struktura a vlastnosti byly zkoumány pomocí NMR, HR-MALDI-MS, IČ spektroskopie, rentgenové analýzy, elektrochemie, UV/Vis absorpční/emisní spektroskopie, diferenční skenovací kalorimetrie, 2PA fluorescenční spektroskopie, generací druhé harmonické a DFT výpočty. Klíčová slova: Push-pull, trifenylamin, cross-coupling, nelineární optika, dvoufotonová absorbce, interkalace.

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CONTENTS 1

Introduction ...................................................................................................................11

2

Theoretical part .............................................................................................................14 2.1 Synthetic approaches to TPA molecules ...................................................................14 2.1.1

Symmetric TPA building blocks...............................................................14

2.1.2

Asymmetric building blocks .....................................................................19

2.2 Modern applications of tripodal push-pull chromophores .......................................23 2.2.1

Fluorescent compounds ............................................................................23

2.2.2

Two-photon absorbers ..............................................................................25

2.2.3

Metal-organic frameworks ........................................................................34

2.2.4

Semiconductors .........................................................................................36

2.3 Other applications of tripodal push-pull systems .....................................................49

3

2.3.1

Analytical technologies.............................................................................49

2.3.2

Biological and medicinal applications ......................................................50

Experimental part .........................................................................................................54 3.1 General methods .......................................................................................................54 3.2 General procedure for the Suzuki-Miyaura cross-coupling (139, 141ql, 155) ........55 3.3 General method for the Sonogashira cross-coupling (140ql, 166, 167) ..................55 3.4 General method for the optimized Sonogashira cross-coupling (145, 146, 147, 148) . ......................................................................................................................55 3.5 General method for the Knoevenagel condensation (142, 143) ...............................56 3.6 General method of the N-methylation of pyridine compounds (150, 152, 154, 156)56 3.7 General method for preparation of carboxylic acids (157, 158, 159) ......................56 3.8 General method for preparation of amides (160, 161, 162) .....................................57 3.9 General method for preparation of nitriles (163, 164, 165) .....................................57 3.10 Chromophore 137 .....................................................................................................57 3.11 Chromophore 138 .....................................................................................................58 5

3.12 Chromophore 139 .....................................................................................................58 3.13 Chromophore 140 .....................................................................................................58 3.14 Chromophore 140q ...................................................................................................59 3.15 Chromophore 140l ....................................................................................................59 3.16 Chromophore 141 .....................................................................................................60 3.17 Chromophore 141q ...................................................................................................60 3.18 Chromophore 141l ....................................................................................................61 3.19 Chromophore 142 .....................................................................................................61 3.20 Chromophore 143 .....................................................................................................62 3.21 Chromophore 144 .....................................................................................................62 3.22 Chromophore 145 .....................................................................................................63 3.23 Chromophore 146 .....................................................................................................63 3.24 Chromophore 147 .....................................................................................................64 3.25 Chromophore 148 .....................................................................................................64 3.26 Chromophore 150 .....................................................................................................65 3.27 Chromophore 151 .....................................................................................................65 3.28 Chromophore 152 .....................................................................................................65 3.29 Chromophore 153 .....................................................................................................66 3.30 Chromophore 154 .....................................................................................................66 3.31 Chromophore 155 .....................................................................................................67 3.32 Chromophore 156 .....................................................................................................67 3.33 Precursor 157 ...........................................................................................................67 3.34 Precursor 158 ...........................................................................................................68 3.35 Precursor 159 ...........................................................................................................68 3.36 Precursor 160 ...........................................................................................................68 3.37 Precursor 161 ...........................................................................................................68 3.38 Precursor 162 ...........................................................................................................69 6

3.39 Precursor 163 ...........................................................................................................69 3.40 Precursor 164 ...........................................................................................................69 3.41 Precursor 165 ...........................................................................................................70 3.42 Precursor 166 ...........................................................................................................70 3.43 Precursor 167 ...........................................................................................................70 3.44 Precursor 168 ...........................................................................................................71 4

Results and discussion ...................................................................................................72 4.1 Design of target D--A chromophores .....................................................................72 4.2 Synthesis....................................................................................................................73 4.3 Physical properties of two-photon absorbers 137–148 ............................................79 4.3.1

Thermal properties ....................................................................................79

4.3.2

Electrochemistry .......................................................................................81

4.3.3

One photon absorption and emission ........................................................83

4.3.4

Two photon absorption (2PA) ..................................................................88

4.3.5

Quantum chemical calculations ................................................................93

4.4 Physical properties of model aminopyridines 149–156 ...........................................96 4.4.1

X-ray crystallography of compound 153 ..................................................96

4.4.2

Electrochemistry .......................................................................................97

4.4.3

UV/Vis absorption spectra ......................................................................100

4.4.4

Quantum chemical calcuations ...............................................................101

4.4.5

Intercalation ............................................................................................103

4.4.6

NLO properties of 149–154 and their intercalates..................................109

5

Conclusions ..................................................................................................................112

6

References ....................................................................................................................116

7

LIST OF ABBREVIATIONS 1PA 2PA 2PIF 2PIP 3PA Ac AIE Ar BHJSC bipy BODIPY Bu BuLi c.-c. CARS DCM DCTB DFT DFWM DHB DIPEA DMF DMSO DNA DPP dppf DSC DSSC FMI FRET HATR Hex HJSC iBu IBX ICT iPr iPrOBpin IR JTSC LED LO Me Mes MIDA m-MTDATA MOF MOP

one photon absorption two photon absorption two photon induced fluorescence two photon induced phosphorescence three photon absorption acetyl aggregation induced emission aryl bulk-heterojunction solar cells 2,2’-bipyridin(yl) boron-dipyrromethene group butan-1-yl n-butyllithium cross coupling reaction coherent anti-Stokes Raleigh scattering dichloromethane 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile density functional theory degenerate four wave mixing 2,5-dihydroxybenzoic acid N,N-diisopropylethylamine dimethylformamide dimethylsulfoxide deoxyribonucleic acid diketopyrrolopyrrole 1,1'-bis(diphenylphosphino)ferrocene differential scanning calorimetry dye sensitized solar cells fluorescence microscopy imaging Förster (fluorescence) resonance energy transfer horizontal attenuated total reflectance n-hexyl heterojunction solar cells isobutyl 1-hydroxy-1λ5,2-benziodoxol-1,3-dione-1-hydroxy-1λ3,2-benziodoxol3(1H)-one 1-oxide intramolecular charge transfer propan-2-yl 1-isopropoxy-3,3,4,4-tetramethyl-2,5,1-dioxoborolane infrared junction type solar cells light emitting diode linear optic methyl 2,4,6-trimethylphenyl N-methyl-imidoacetic acid 4,4′,4′′-tris[phenyl(m-tolyl)amino]triphenylamine metal organic framework metal organic polymer 8

MPI NBS NCS NIS NLO NLT NMP Oct OKE OLED OSC PCF PDT Ph PLED Pr SNAr TBAF tBu TCPA TCTA Td TEA TFAA TFATA Tg THF TIPA TLC Tm TMS TMSA Tol TPA TPFI TPPA Ts UV Vis

multiphoton induced N-bromosuccinimide N-chlorosuccinimide N-iodosuccinimide nonlinear optic non linear transmission N-methyl-2-pyrrolidone n-octyl optical Kerr effect organic light emitting diode organic solar cell piezofluorochromism photodynamic therapy phenyl polymeric light emitting diode propan-1-yl nucleophilic aromatic substitution tetrabutylammonium fluoride tert-butyl 4',4'',4'’'-nitrilotris(([1,1'-biphenyl]-4-carboxylic acid)) tris(4-carbazoyl-9-ylphenyl)amine temperature of thermal decomposition triethylamine trifluoroacetic acid anhydride 4,4,4-tris[9,9-dimethyl-2-fluorenyl(phenyl)amino] triphenylamine glass transition temperature tetrahydrofurane 4,4’,4’’-tris(imidazol-1-yl)triphenylamine thin-layer chromatography melting point trimethylsilyl ethynyl(trimethyl)silane 4-methylphenyl triphenylamine two photon fluorescence imaging 4,4’,4’’-tris(pyridin-4-yl)triphenylamine 4-toluensulfonyl ultraviolet visible

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AIMS OF THE DISSERTATION A general aim of this dissertation was to design and synthesize new push-pull chromophores with second- and third-order nonlinear optical properties. The following projects were proposed within the scope of this work: 1. A systematic modulation of (non)linear optical properties in tripodal molecules based on triphenylamine by variation of the peripheral acceptors. 2. A development of new aromatic electron withdrawing moieties. 3. A systematic study of branching effect in push-pull molecules and its influence on the optoelectronic properties. 4. A development of model guest D--A molecules for intercalation into layered inorganic host materials.

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1 Introduction Tripodal push-pull molecules represent an advanced arrangement of more common linear D--A systems. In general, tripodal molecules may adopt two parent arrangements (Figure 1): centrifugal D-(-A)3 and centripetal A-(-D)3. Whereas the first type contains a central electron donor (D) and three peripheral acceptors (A) connected via a -system, the second one is vice versa. According to the current state-of-the-art and despite the recent progress in the synthesis of centripetal molecules,1,2 the centrifugal arrangement is much more frequent, most likely due to its easy synthetic availability. In such push-pull molecules, an intramolecular

charge-transfer

(ICT)

from

the

central/peripheral

donor

to

the

peripheral/central acceptor takes place and the molecule become highly polarized. Thus, the molecular periphery is being charged negatively or positively, whiles the central part vice versa. This represent very unique feature of tripodal molecules. Beside already mentioned linear and tripodal push-pull molecules, the current literature offers also extraordinary chromophore arrangements such as T-shaped,3 X-shaped4 and Y-shaped5 molecules. The latter Y-shaped molecules can also be considered as tripodal or so-called starshaped/octupolar.

Figure 1. Two general arrangements of tripodal push-pull molecules.

The most widely explored centrifugal D-(-A)3 tripodal molecules are undoubtedly based on triphenylamine (N,N-diphenylaminobenzene, N,N-diphenylaniline) central donor. Triphenylamine will be in this work further abbreviated as TPA (Figure 2).

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Figure 2. Structural formula (a), DFT optimized (B3LYP/6-311++G(2d,p)) spatial arrangement (b) and ORTEP view (c) of the parent TPA molecule.

TPA possesses unique geometric6 as well as electronic properties7,8 and noticeable chemical stability9 which, alongside with its well explored chemistry, makes him a very attractive moiety for materials chemistry, especially dye and photonic chemistry. N,N-Diphenylamino group is considered as electron-donor with slightly less donating ability than N,N-dialkylamino groups (Hammett substitution constants p = -0.56 vs. -0.83).10 The DFT optimized structure of TPA (Gaussian 09) reveals its nonplanar arrangement with two phenyl rings forced out of the mean plane with central CNCC torsion angles of 43 and 42  (39 and 45 ° in the gas phase),6 which is in agreement with the solid state structure determined by X-ray analysis (torsion angles 43 and 46 °, respectively).11

Figure 3. Representative first triphenylamine derivatives 1–2 TPA based azo dye 3 and first tripodal molecule 4.

12

The first examples of TPA-derived molecules 1 and 2 can be dated back to the end of 19th century,12,13 while between the world wars a series of triphenylamine based azo-dyes 3 was patented (Figure 3).14 In the same era, 4-phenyl-N,N-bis(4-phenylphenyl)aniline 4 has been denoted as the first tripodal push-pull system.15,16 Laser invention, increased knowledge on experimental photon physics17 and quantum chemistry as well as fast developing organic synthesis in the second half of the 20th century further promoted great research activity directed towards tripodal molecules. Shortly, their huge potential in advanced photonics and organic semiconductors has been realized and definitely has terminated the era of their applications as ordinary dyes. Tripodal molecules having push-pull arrangement were mainly applied as nonlinear optically (NLO) active DA molecules with tunable properties.18 Hence, this literature search focuses on tripodal, centrifugal and mainly TPA-based push-pull chromophores. The synthetic approaches leading to such molecules and the most successful applications will be discussed in the subsequent chapters.

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2 Theoretical part 2.1

Synthetic approaches to TPA molecules

In general, there are two synthetic approaches to build up tripodal push-pull TPA molecules. The most widely used one involves derivatization of the parent TPA. In this way, symmetric molecules are often being synthesized. The main advantage of this approach can be seen in a reduced number of reactions steps, synthetic easiness, less number of starting materials (usually only TPA) and modular access to a large number of derivatives. This approach is summarized in chapter 2.1.1. In contrast to the aforementioned approach, the second one involves building of the TPA core during the synthesis. This method allows the synthesis of asymmetric building blocks and target molecules. This approach is also useful for the synthesis of building blocks which are less accessible via direct TPA derivatization either for economic or synthetic reasons. The second strategy is summarized in chapter 2.1.2. 2.1.1

Symmetric TPA building blocks 2.1.1.1 Halogenated intermediates The most widely used and universal TPA-based strategic intermediates are

undoubtedly 4,4’,4’’-tribromo- (5) and 4,4’,4’’-triiodotriphenylamine (6). Halogenated TPA compounds such as 5 and 6 represent suitable substrates for various cross-coupling reactions,19,20 threefold lithiations21 and other possible electrophilic derivatization. These molecules are well-accessible via halogenation of the parent TPA molecule employing various conditions (Scheme 1).

Scheme 1. General halogenation of TPA.

The classical iodination22–24 of TPA utilizes molecular iodine and mercury(II) oxide as a Lewis acid in ethanol. The attained yields of 6 vary from 50 to 85 % while toxicity of the mercury oxide should also be considered. Hence, other iodination systems were also sought. The modern electrophilic iodinating agents involve IPy2BF4 (Ref.25) or BnNMe3ICl2 (Ref.26) 14

in halogenated solvents and redox systems such as IBX/I2 (Ref.27), KIO3/KI (Ref.28–30) or NCS/NaI (Ref.31). These reagents proved to be more environmentally friendly and often deliver excellent or almost quantitative yields. The ordinary iodinating agent NIS was also reported to iodinate TPA in chloroform/acetic acid with exclusion of the light.32 TPA threefold bromination is much easier reaction than iodination due to its limited reversibility. Standard bromination agents such as NBS in basic solvents and/or in the presence of an additional base33,34 and molecular bromine in halogenated solvents such as chloroform, DCM35 or tretrachloromethane36,37 afforded 5 in excellent to almost quantitative yields. 2.1.1.2 Non-halogenated intermediates A reversal alternative to halogenated substrates 5 and 6 applicable in cross-coupling reactions are 4,4’,4’’-metalotriphenylamines. However, such TPA-derived coupling partners are less known most likely due to lack of their chemical stability, tedious synthesis and possible

reverse

cross-coupling

reactions.

On

the

other

hand,

triphenylamine-4,4’,4’’-trisboronic acid respective its trispinacol ester 7 has routinely been used as a substrate for threefold Suzuki cross-coupling reactions.38–40 Compound 7 is accessible from 5 (or 6) by a threefold lithiation and subsequent substitution with 1-isopropoxy-3,3,4,4-tetramethyl-2,5,1-dioxoborolane (iPrOBpin).41 Starting from 5, this reaction provides yields not overcoming 65 % (Scheme 2).42,43 Tribromo derivative 5 can also be treated with bis(pinacolato)diboron in terms of cross-coupling reaction. This reaction is usually being carried out in etheric solvents and in the presence of O-bases and microwave irradiation, which may increase the attained yields up to 70-89 % (Scheme 2).44,45 Direct electrophylic C-H borylation represents another synthetic route leading to 7. Starting from TPA and using borylation system such as BCl3/AlCl3/Me2NTol and subsequent esterification with pinacol in the presence of N-methyl-imidoacetic acid (MIDA)46,47 seems to be the most promising and easiest reaction sequence leading to 7 (Scheme 2).

Scheme 2. Synthetic routes to trisboronate 7.

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4,4’,4’’-Triethynyltriphenylamine 8 (Ref.48,49) represents versatile substrate for Sonogashira cross-coupling or Huisgen [3+2] cycloaddition.50 Triacetylene 8 is accessible from 5 or 6 by Sonogashira cross-coupling with ethynyltrimethylsilane (TMSA) or dimethylethynylcarbinol followed by protecting group removal (Scheme 3).

Scheme 3. Threefold Sonogahsira reaction leading to terminal triacetylene 8.

Similarly, 4,4’,4’’-trivinyltriphenylamine 9 (Ref.51) is also well known substrate for threefold Heck cross-coupling reactions. This compound can conveniently be synthesized from triscarbaldehyde 10 by Wittig reaction with methyltriphenylphosphonium salts (Scheme 4).52 For the synthesis of 10 see the subsequent paragraph.

Scheme 4. Wittig synthesis of 4,4’,4’’-trivinyltriphenylamine 9.

Triphenylamino-4,4’,4’’-triscarbaldehyde 10 is considered as one of the most versatile building blocks for the construction of tripodal TPA derivatives. It can easily be obtained from 5 or 6 by triple lithiation and subsequent reaction with DMF (Scheme 5).53 Triple formylation can also be achieved by Vilsmeyer-Haack reaction (Scheme 5).54 It has been demonstrated that this triscarbaldehyde undergoes smooth Wittig (see above)51 or Knoevenagel reactions55 as well as other olefinations.

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Scheme 5. TPA formylations leading to triscarbaldehyde 10.54,56

4,4’,4’’-Trisacetyltriphenylamine 11 is another carbonyl compound widely employed in the construction of TPA-derived molecules. Triketone 11, which can be easily prepared by Friedl-Crafts acylation of the parent TPA,57 proved to be suitable intermediate for the construction of heterocyclic moieties58 as well as triphenyl-4,4’,4’’-tricarboxylic acid 12 (Scheme 6).59 The latter compound can be synthesized from 5 and its gradual lithiation and reaction with CO2(s); however this reaction proved to be sluggish.60

Scheme 6. Friedl-Crafts acylation and subsequent haloform reaction of triketone 11.

Peripheral substituents can also be attached to TPA via amino groups. Hence, tris(4-aminophenyl)amine

13,

which

can

be

prepared

from

the

corresponding

trinitroderivative 14 (Scheme 7),61 seems to be also very crucial derivative. Triple nitration of TPA by a mixture of nitric and glacial acetic acids afforded smoothly desired trinitrotriphenylamine 14.62–65 Compound 13 is being almost exclusively prepared from 14 either by Pd-catalyzed hydrogenation66,67 or by reduction using Sn/HCl.63,68 Beside the aforementioned standard nitration of TPA, trinitro derivative 14 can also be synthesized via stepwise nucleophilic substitution or copper (I) catalyzed cross-coupling reaction using halogenated nitrobenzene and 4-nitroaniline (Scheme 8).61,69

17

Scheme 7. TPA nitration and subsequent reduction of 14 to triamine 13.

Scheme 8. C-N bond formation via SNAr or cross-coupling reaction.

Although not TPA derivative, symmetrically substituted trinaphthylamine 15 can be synthesized from the corresponding amine and naphthylbromide via twofold BuchwaldHartwig reaction (Scheme 9).70,71 In contrast to aforementioned Cu(I)-catalyzed Ullman reaction, Buchwald-Hartwig reaction is catalyzed by Pd/phosphine system including cesium carbonate as a base.

Scheme 9. Buchwald-Hartwig cross-coupling reaction leading to trinaphthylamine 15.

Figure 4 lists some other S-, O- and P-precursor 16–18 that would serve as building blocks for the construction of tripodal systems but have not yet been used. These molecules involve trisulfonic acid 16, triole 17 and dichlorophosphanyl derivative 18.62,72,73

18

Figure 4. Other TPA derivatives suitable for the construction of tripodal molecules.

2.1.2

Asymmetric building blocks In general, all the aforementioned functional groups present in symmetrical derivatives

5 to 18 can be combined in one TPA core to gain asymmetric TPA derivatives. However, the most widely combined functional groups are halogens, formyl, boronates and nitro. These groups are usually combined at one TPA core in 2:1 ratio. TPA derivatives having three different substituents attached to the particular phenyl ring are scarce, most likely due to their tedious preparation. The subsequent chapter will deal with such asymmetrically substituted TPA derivatives. Triphenylamine-4-carbaldehyde 19, which is accessible via partial Vilsmeyer-Haack reaction (see above), can be twofold iodinated to derivative 20. Diiodo derivative 20 undergoes

twofold

Heck

olefination

or

Sonogashira

reaction

to

derivatives

21 and 22 (Scheme 10).74–76

Scheme 10. Iodination of monoaldehyde 19 and its subsequent modifications via Heck and Sonogashira reactions.

Tribromo TPA 5 can be mono lithiated using 1 eq. of BuLi, treated with trimethyl borate and subsequently esterified with pinacol to dibromo boronate 23. This precursor has been

applied

in

twofold

Suzuki-Miyaura

cross-coupling

reaction

with

dibromo

diketopyrrolopyrrole (DPP) derivative to afford molecule 24 in 65 % yield (Scheme 11).77 19

Scheme 11. Synthesis of asymmetric intermediate 23 and its use in cross-coupling reaction.

Triphenylamine can also be selectively mono brominated to 25 (Ref.78,79) and subsequently diiodinated to

26

(Scheme 12).79

Chemoselective

twofold

Hiyama

cross-coupling reaction can be performed with this precursor leading to molecule 27.

Scheme 12. Bromodiiodo derivative 26 and its chemoselective Hiyama cross-coupling.

The aforementioned electrophilic modifications of the parent TPA (may) suffer from equilibrium character,57 low chemoselectivity80 and reduced yield of the desired, triple substituted TPA derivative.69,81 Hence, other synthetic approaches have also been developed. Two most widely used methods involve one- or twofold nucleophilic aromatic substitutions82, and C-N cross-coupling reaction, copper(I)-catalyzed Ulmann reaction in particular.83–85 Although the attained yields of such reactions are not very high, the fact that they utilize inexpensive and readily available materials makes them also attractive. Synthesis of trinitro TPA 14 (Scheme 8) is one of such example. Figure 5 list another selected examples 28–30 that can be prepared in a similar way.86,87,88 20

Figure 5. Asymmetric TPA derivatives available either by C-N cross-coupling or nucleophilic substitution.

A

chemically

interesting

acid-catalyzed

reaction

of

a

diarylamine

with

cyclohexanedione has been reported by Kaneko et al. (Scheme 13).89 This reaction utilizes inexpensive starting materials and provides relatively direct access to asymmetric building blocks 31 and 32.

Scheme 13. Synthesis of asymmetric building blocks 31 and 32.

Modern C-N bond formation reactions are increasingly being used in the synthesis of large asymmetric tripodal TPA push-pull chromophores90,91 as well as dendritic92 and polymeric93 compounds. Building and further extension of asymmetric TPA core can be accomplished

via

modified

Cu(I)-catalyzed

Ulmann

reaction

(Scheme

14).94–96

Chemoselective reaction between 4-bromophenylbiphenylamine and iodobiphenyl afforded asymmetric tripodal system 33 in 65 % yield.

Scheme 14. CuCl and phenanthroline catalyzed Ullman reaction.

Buchwald-Hartwig cross-coupling has also been used for the construction of molecule 34 which possesses large -conjugated scaffold with peripheral oxadiazole rings and TPA central core (Scheme 15). 97–100 21

Scheme 15. Construction of multicore tripodal system 34 via Buchwald-Hartwig cross-coupling.

22

2.2

Modern applications of tripodal push-pull chromophores

Modern applications of tripodal molecules are derived mainly from their peculiar intrinsic properties such as their optical properties as well as their geometric arrangement (star-shaped molecules). Hence, current use of tripodal molecules range from bright fluorescent dyes (FRET technologies, bioimaging, two-photon absorption), semiconductors (hole transporting materials, electroluminescent/electrochromic materials, photovoltaics), ligands used in construction of metal-organic frameworks to analytical, biological and medicinal applications. Particular applications will be summarized and discussed in the following chapters. 2.2.1

Fluorescent compounds In fact, observed large emissive behavior of tripodal molecules has initiated a wide

research interest of material chemists directed towards these materials.101,102 Their substantial fluorescent properties have been used in FRET as well as fluorescence bioimaging technologies.103 The main advantage of TPA-derived materials can be seen in an easy synthesis and high level of modularity. Hence, the emission of the given fluorophore can easily be tuned by appending various peripheral moieties. It has also been demonstrated that fluorescence of multibranched molecules is not a simple summation of the fluorescence of the particular branches. This important issue has been addressed in the work of Choue et al. that have theoretically and experimentally investigated gradual branching of TPA with 3-hydroxyflavone (HF) moieties (35a–c, Figure 6).104

Figure 6. Gradual substitution of TPA with 3-hydroxyflavone units and its impact on the optical properties (dichloromethane).

Benzophenone and BODIPY proved to be interesting peripheral moieties that in combination with central TPA deliver strong emissive compounds 36 and 37 (Figure 7). 105,106 These two compounds proved to be practically promising fluorescent materials.

23

Figure 7. Benzophenone- and BODIPY-based fluorescent TPA derivatives.

Relatively simple TPA-based succinimide/maleinimide fluorophores 38 attracted considerable attention for their relatively easy thermal switching between 38a and 38b (Scheme 16).

69

Whereas the isomer 38a with exocyclic double bond possesses weak

succinimide acceptor (low ICT and high fluorescence), isomer 38b bears three strong peripheral maleinimide acceptor groups that enhanced the ICT and suppressed the fluorescence. In this way, the (non)emissive behavior can easily be triggered.

Scheme 16. Thermo-triggered switching of the emissive properties in 38.

D-(-A)3 and dendritic D-(-D)3 derivatives 39 and 40 bearing peripheral quinoline and carbazole acceptors/donors can be denoted as fluorophores with advanced applications (Figure 8).58,107 These molecules belong to few noble, non-polymeric materials showing 24

external pressure fluorescence enhancement, piezofluorochromism (PCF) and found manifold applications as mechanosenzors, security dying and data storage materials.

Figure 8. Push-pull and push-push molecules 39 and 40.

2.2.2

Two-photon absorbers Absorption of two photons represents one of the most studied third order nonlinear

optical phenomena. This process, referred to as 2PA, namely 2PA cross-section ((2) or 2PA), is widely used parameter to consider applicability of the given chromophore in various modern optoelectronic applications.18,108 The first theoretical description of molecule excitation state resulting from the absorption of two photons (instead of more common one-photon absorption) has been reported in dissertation thesis of Maria Göppert-Mayer in 1931.109 Later in 1963 M. GöppertMayer has been awarded by Nobel Prize in Physics “for discoveries concerning nuclear shell structure.” In her dissertation work, most of the current 2PA theory has been given. The most fundamental aspect of 2PA can be seen in energies of two photons absorbed by the molecule. In general, the sum of excitation energies of these photons E(1) and E(2) corresponds to the difference between two allowed electronic states of molecule, therefore E(exc.) = E(1) + E(2). Simultaneous absorption of two photons with different energies (E(1) ≠ E(2)) is called nondegenerate 2PA. Despite the fact, that nondegenarate 2PA has many potential industrial and medicinal applications,110 the complex mathematics as well as experimental physics of this phenomena distracts attention of scientists. On the other hand, degenerate 2PA, in which 25

two photons with the same energies were consecutively absorbed (E(1) = E(2)), is mathematically and experimentally more friendly. The vast majority of current studies in the field focuses on this phenomena. The degenerate 2PA can mathematically be simplified up to relatively trivial Equation 1.108 In general, the ground and excited states of a molecule can be divided into gerade (g, even) and ungerade (u, odd) states. In centrosymetric molecules (particular D--A-D or A--D--A quadrupolar systems), only the g → u transfers are allowed and represent odd photon absorptions processes (1PA and 3PA). Even photon absorption process, however, must involve g → g or u → u transfers. This means that one-photon allowed excitations of quadrupolar molecules are two-photon disallowed and vice versa. This non-equivalency of even an odd photon excitation represents certain obstacle in experimental 2PA measurement in centrosymmetric molecules. On the other hand, in noncentrosymmetric systems (linear or tripodal) both transitions are simultaneously allowed. This fact has considerable impact on measuring 2PA in such systems. Thus, tripodal shape of parent triphenylamine (Figure 2) and whereon build push-pull molecules represent very promising structural pattern with easily recordable 2PA activity.111 R – atomic transition rate

 2  I 2 R 

(2) – 2PA cross-section I – radiation intensity ω – angular velocity of radiation Equation 1. Basic rate equation of 2PA.

Considering the fact that two photon excitation energies (represented in the Equation 1 as ω) are lying in the near infrared regions (half of the energy of 1PA lying usually in UV/Vis area) and 2PA cross-section (2) parameters are usually in order of 10-50 cm4.s.photon-1 (often reported as GM in honor of the aforementioned inventor of 2PA phenomena), the radiation intensities I required for measurable atomic transition rate must exceed 1.1010 W.cm-2. Hence, the first experimental verification of 2PA, theoretically predicted by M. Göppert-Mayer already in 1931, had to wait more than 30 years until the laser has been invented by T. H. Maiman in 1960.112 According to the Equation 1, 2PA cross-section (2) (also referred as

TPA) along with the wavelength of the maximal 2PA outcome are considered as the key material parameters of the given push-pull molecule. In contrast to initial experiments carried out with inorganic solids112 or in gas phase,113 current (2) measurements focusing on organic chromophores are mainly accomplished in transparent solutions.114 26

Three different types of measurements of the aforementioned parameters are currently used: 

The most developed are direct methods of measurement such as Z-scan and nonlinear transmission experiment (NLT). These methods usually allow easy experimental setup, are considered to be precise and do not operate with the chromophore fluorescence but require concentrated solutions.



The variety of indirect methods such as two photon induced fluorescence (phosphorescence) - 2PIF(P), thermal lensing or multiphoton induced (MPI) spectroscopy are more predicative in cases when the fluorescence part of 2PA is important for the material. However, non-fluorescent chromophores cannot be measured by these methods.



Wave mixing methods such as coherent anti-Stokes Raileigh scattering (CARS), degenerate four wave mixing (DFWM) and optical Kerr effect (OKE) allow determination not only 2PA parameters but also other third order nonlinear properties such as third order polarizability  and third order susceptibility (3).111

From the theory introduced above we can deduce that octupolarity of tripodal pushpull systems would significantly enhance the (2) coefficient.18 This quantum chemical postulate has firstly been verified by an experiment on TPA molecule 41 bearing oxadiazine acceptor (Figure 9).115 The first 2PA results on 41 were almost immediately verified by other research groups.116,117 In agreement with the theory, 2PA cross-section in tripodal molecules tends to be higher than simple summing contributions of particular branches.115

Figure 9. First tripodal 2PA chromophore.

27

In the following text I would summarize and discuss recent advances in this area of 2PA molecules. As there is still little known about detailed structure-2PA activity relationships, the currently available data will be critically assessed with the emphasis put on the relations between the structure of the chromophore and its 2PA response.

Figure 10. TPA chromophores 42-51 bearing various peripheral acceptors linked via olefinic unit. Table 1. Linear and nonlinear optical data of compounds 42–51.

maxA (solvent)

maxE (solvent)

 (solvent)

[nm]

[nm]

[%]

42

452 (DMF)

510 (DMF)

6 (DMF)

57.6 (780, DMF)

Ref.118

43

503 (DMF)

523 (DMF)

11 (DMF)

19.4 (780, DMF)

Ref.118

44

397 (DMF)

530 (DMF)

16 (DMF)

66.1 (780, DMF)

Ref.118

45

398 (DMF)

522 (DMF)

38 (DMF)

19.8 (780, DMF)

Ref.118

46

396 (DMF)

536 (DMF)

6 (DMF)

330.8 (780, DMF)

Ref.118

47

387 (DMF)

527 (DMF)

10 (DMF)

38.4 (780, DMF)

Ref.118

48

435 (toluene)

498 (toluene)

93 (toluene)

2028 (740, toluene)

Ref.51

49

554 (DMSO)

-

-

25318 (800, DMSO)

Ref.119

50

440 (toluene)

480 (toluene)

73 (toluene)

1000 (740, toluene)

Ref.120

51

433 (DCM)

538 (DCM)

54 (DCM)

354 (740, DCM)

Ref.121

Comp.

(2) (exc [nm]; solvent) -50

[10

4

-1

References

cm .s.photon ]

The first series of compounds worth to be discussed here are A-vinyl substituted TPA molecules 42–51 (Figure 10, Table 1). In these molecules, varied peripheral acceptors were linked via olefinic unit to TPA core. When going from cyano-substituted 42 to 43 and subsequently to 44/45 the NLO response decrease for tricarboxylic acid 43 and slightly increase for methyl ester 44. Different (2) coefficients of 44 and 45 demonstrates influence of the alcoholic part of the ester terminal function on the 2PA activity. Pyridyl substituted molecule 46 showed much higher 2PA response than previous simple NLOphores 42–45. However, this NLO activity diminishes when the pyridyl moiety is connected in a 28

nonsymmetrical manner as in 47. Complex acceptor units such as 9H-fluorene (48), pyridinium (49), borane (50) or benzo[d]thiazole (51) generally brings much higher 2PA activity than simple functional groups such as in 42–45. Simple pyridine N-quaternization and thus ICT enhancement in molecules 46 vs. 49 (pyridyl vs. pyridinium acceptors) resulted in increase of 2PA coefficient (2) in one order of magnitude.

Figure 11. Complex acceptor units linked to TPA core via acetylenic spacer. Table 2. Linear and nonlinear optical data of chromophores 52–62.

maxA (solvent)

maxE (solvent)

 (solvent)

[nm]

[nm]

[%]

52

404 (toluene)

434 (toluene)

80 (toluene)

459 (740, toluene)

Ref.

48

53

440 (toluene)

512 (toluene)

61 (toluene)

2275 (800, toluene)

Ref.

48

54

480 (toluene)

594 (toluene)

29 (toluene)

922 (740, toluene)

Ref.

48

55

403 (toluene)

417 (toluene)

94 (toluene)

375 (820, toluene)

Ref.

56

377 (THF)

428 (THF)

58 (THF)

91 (770, THF)

Ref.

22

57

391 (THF)

455 (THF)

55 (THF)

280 (800, THF)

Ref.

22

58

405 (toluene)

450 (toluene)

78 (toluene)

495 (740, toluene)

Ref.

122

59

408 (toluene)

473 (toluene)

79 (toluene)

1080 (740, toluene)

Ref.

122

60

528 (toluene)

543 (toluene)

93 (toluene)

108 (700, toluene)

Ref.

123

61

685 (THF)

757 (THF)

13.3 (THF)

8100 (800, THF)

Ref.

124

62

645 (THF)

745 (THF)

9.5 (THF)

11800 (800, THF)

Ref.

124

Comp.

(2) (exc [nm]; solvent) -50

[10

4

-1

cm .s.photon ]

References

120

A similar series of compounds 52–62 bearing acetylenic instead of olefinic unit can also be collected as shown in Figure 11 and Table 2. The first sub-series of chromophores is represented by molecules 52–54 that possess peripheral benzo[d]thiazole acceptor unit. 29

As can be seen, additional DCV unit attached to the heterocycle shifted the absorption maxima bathochromically as well as increased the 2PA activity. Moreover, on these molecules we can demonstrate how crucial acceptor positioning is. Whereas DCV connected to the fused benzene ring enhances the cross-section almost five-times (53), reversal connection as in 54 resulted in much weaker response (matched/mismatched connection). Molecules 55–59 possess various acceptor units such dimesitylboran (55), pyridin-4-yl (56–57)

and

trifluoromethylsulfonyl

group

(58-59).

When

comparing

analogous

chromophores 55/50 and 56–57/46 (Table 2 vs. Table 1), we can see that the later ones, in which the acceptor is linked via olefinic spacers, always deliver higher two-photon absorption cross-section. Hence, the olefinic unit seems to be more polarizable than acetylenic ones. An extension of the -system and its impact on (non)linear optical properties can be shown in molecules 56–57 and 58–59; extension of the linker lead to increased NLO response. Porphyrin used as peripheral acceptor group as in TPA derivatives 61 and 62 delivered exceptionally red-shifted max and very high 2PA response. Third family of currently well-investigated 2PA absorbers I would like to mention here are molecules 63–69 (Figure 12 and Table 3). A joint feature of these molecules is the presence of three stilbenyl arms bearing substituted benzenes used as peripheral acceptors/donors. From the cyano-substituted compounds 63–66, DCV in 64 showed the most efficient electron withdrawing behavior and shifted the CT-band up to 487 nm and, jointly with 66, also delivered the highest 2PA response. In contrast to compounds 58 and 59 (Figure 11, Table 2), trifluoromethylsulfonyl derivatives 67 and 68 build on polarizable stilbenyl spacers showed max red-shifted by ~30 nm and significantly enhanced two-photon absorption cross-section (495/1080 vs. 1340/2070 GM for 58/59 and 67/68). Triazine used as an terminal acceptor as in 69 showed only moderate 2PA activity with (2) equal to 766 GM. Beside the aforementioned ordinary D-(π-A)3 systems, Figure 13 shows another examples of various chromophore arrangements. Whereas molecule 70 can be considered as common D-(π-A)3 system, 71 and 72 represent triazine-based A-(π-D)3 and planarized D-(π-D)3 systems. As can be seen from the Table 4, centripetal A-(-D)3 arrangement as in 71 brings over centrifugal D-(-A)3 one (70) bathochromically shifted absorption maxima, however the 2PA response is diminished. Three peripheral donors connected to TPA core as in D-(-D)3 system 72 shifted the max to 411 nm and delivered considerably high two-photon cross-section of 4800 GM. 30

Figure 12. Triaryl chromophores bearing stilbenyl -linker. Table 3. Linear and nonlinear optical data of chromophores 63–69.

maxA (solvent)

maxE (solvent)

 (solvent)

[nm]

[nm]

[%]

63

415 (toluene)

467 (toluene)

95 (toluene)

220 (760, toluene)

Ref.

125

64

487 (toluene)

570 (toluene)

41 (toluene)

1200 (890, toluene)

Ref.

125

65

464 (toluene)

550 (toluene)

33 (toluene)

740 (890, toluene)

Ref.

125

66

450 (toluene)

519 (toluene)

69 (toluene)

1360 (800, toluene)

Ref.

125

67

430 (toluene)

494 (toluene)

71 (toluene)

1340 (740, toluene)

Ref.

51

68

440 (toluene)

517 (toluene)

84 (toluene)

2070 (800, toluene)

Ref.

51

69

437 (CHCl3)

536 (CHCl3)

32 (CHCl3)

766 (800, CHCl3)

Ref.

Comp.

(2) (exc [nm]; solvent) -50

[10

4

-1

cm .s.photon ]

References

126

Further development in the field also revealed that D-(π-A-π-D)3 arrangement with an peripheral donor attached to an acceptor linked to a central donor seems to be also beneficial and significantly enhances 2PA responses.127 Thus, molecules 73–75 (Figure 14) represent an alternative to more common aforementioned D-(π-A)3 systems. The data gathered in Table 4 reveals significantly red-shifted absorption maxima for 73 and 74 and also high 2PA coefficients of 5030 and 3299 GM. In contrast to this, molecule 75 bearing triazol spacer/acceptor showed hypsochromically shifted CT-band and only very weak 2PA activity. Although recent investigations on solvatochromic behavior of tripodal compounds has shown some trends (mainly dependence of the NLO response on the solvent polarity),128,129 influence of the solvent on 2PA activity remained not fully revealed yet. Hence, the solvent should always be specified.

31

Figure 13. Selected examples of other chromophore arrangements. Table 4. Linear and nonlinear optical data of chromophores 70–75.

maxA (solvent)

maxE (solvent)

 (solvent)

[nm]

[nm]

[%]

70

392 (-)

-

-

27000 (-,-)

Ref.

71

421 (CHCl3)

535 (CHCl3)

27 (CHCl3)

447 (800, CHCl3)

Ref.2

72

411 (toluene)

438 (toluene)

53 (toluene)

4800 (650, toluene)

Ref.

131

73

495 (toluene)

536 (toluene)

67 (toluene)

5030 (840, toluene)

Ref.

132

74

492 (CHCl3)

553 (CHCl3)

16 (CHCl3)

3299 (700-880, CHCl3)

Ref.

133

75

347 (toluene)

387 (toluene)

49 (toluene)

240 (577, toluene)

Ref.

Comp.

32

(2) (exc [nm]; solvent) -50

[10

4

-1

References

cm .s.photon ] 130 ,126

50

Figure 14. D-(-A--D)3 chromophore arrangement.

33

2.2.3

Metal-organic frameworks The unique geometry of parent TPA134 and whereon build molecules has always been

of high interest for supramolecular coordination organometalic chemistry. The interesting crystallography of such species,135,136 studied thoroughly with various combinations of ligands and metals from the beginning of 21st century,137 has revealed multiple molecular engineering opportunities such as tunable organometallic molecular magnets,138 molecular frameworks involved in gas storage,139 optoelectronic applications140 and luminescent detectors.141 Figure 15 shows two most widely employed ligands 76 and 77 in metal organic framework (MOF) and metal organic polymer (MOP) chemistry. These molecules, namely 4,4’,4’’-tris(pyridin-4-yl)triphenyl amine (76)142 and 4,4’,4’’-tris(imidazol-1-yl)triphenyl amine (77)142,143 are often referred as TPPA and TIPA, respectively. Whereas 76 represents D-(-A)3 system bearing weak pyridin-4-yl acceptors, 77 is an example of D-(-D)3 system with three electron rich imidazole rings.

Figure 15. The most used TPA-based MOF templates - TPPA (76) and TIPA (77).

The electron withdrawing properties of pyridine group in 76 can further be enhanced by their coordination to zinc,144 cadmium,144 cobalt,144 copper20 or nickel142 salts to achieve a strong D-(-A)3 system yet applicable in optoelectronic devices. On the other hand, chelation of the imidazole lone electron pair in 77 would switch D-(-D)3 to D-(-A)3 system with interesting electronic and optical consequences.145 An example of such molecular “umpolung” is given in Scheme 17. Notably, such coordination may not only enhance or switch donor-to-acceptor properties of certain molecules, but also build longer and more efficient -conjugated system. This approach has already been successfully tested in semiconducting technologies, e. g. OLED applications of pyridine derivatives146 and seems to be promising also for tripodal147 and polymeric148 benzimidazole TPA molecules. Reversible ON/OFF switching would also allow for metal ion detection.149 34

Scheme 17. “Umpolung” of TIPA (77) via chelation.

Relatively simple cyano- (78),150 tetrazole- (79)135 and carboxyl-substituted (80)151 TPA molecules (Figure 16) have not very interesting (N)LO or electrochemical properties. Nevertheless, these molecules proved to be great and accessible substrates generating MOF materials. For instance, molecule 78, also referred as TCPA, is known to form at least three MOFs with silver(I) ions.150 These supramolecular assemblies are considered as promising data storage materials. A cross linked analogue of 78 has recently been reported to create similar complexes also with gold(III) ions.152

Figure 16. TPA-based push-pull MOF precursors 78–80.

Tendency of MOFs to self-assembly140,153,154 is also often used for crystal stabilization. Hence, tripodal D-(-A)3 compounds and whereon build MOFs delivered materials with stable properties applicable in dye sensitized solar cells.140 In some TPA-based MOFs, the TPA ligand chirality, generally not observable, appears to be locked. Hence, it would be very challenging to generate MOF-based chiral photonic materials.155

35

2.2.4

Semiconductors Tripodal push-pull molecular arrangement has shown multiple advantages in organic

semiconductor technologies. Tunable properties such as crystallinity (crystalline/liquid crystalline/amorphous character),156 transparency157 as well as suitable electronic properties are directing their semiconducting applications towards hole transporting materials, organic light emitting diodes (OLEDs), photovoltaic cells (JTSCs, DSSCs) and some other notable applications. The most successful tripodal push-pull molecules and their applications in such areas will be discussed in the following chapters. 2.2.4.1 Hole transporting materials TPA-based molecules have been used as hole transporting materials since the first patents and publications on multi-layered organic semiconductor technologies had been released in late 90ths.158,159 Diphenylamino-,158,160 carbazole-32,161 or later also ferrocenederived162 D-(-D)3 TPA molecules celebrated great success as semiconductors, which can be nowadays demonstrated by the large number of commercial multi-layered devices.163 Many of the aforementioned molecules named as m-MTDATA,164 TCTA165 or TFATA166 are currently also commercially available organic semiconductors and significantly affected research of the LED technology.167,168 The high importance of TPA-based polymers or dendrimers in this field should also not be neglected.169,170 TPA molecules also form stable radicals which may act as promising hole-transporting materials.171 The fundamental requirements of a holetransporting material are well suited electronic properties (HOMO/LUMO levels), high conductivity and transparency as well as stable amorphous167 or liquid crystalline character in the solid state.23 Thermal robustness and good processability via vacuum deposition are also highly demanding.172 For instance, it has been shown that relatively simple azo- (Ref.173) or hydrazone-based D-(-A--D)3 molecules such as 81 (Figure 17) have lower glass transitions temperatures (Tg), higher melting point (Tm) and lower oxidation potentials comparing to the aforementioned commercial D-(-D)3 materials. This can be considered as a good promise for its further semiconductiong applications.174–176 TPA derivatives with either low Tg (e.g. 82 with Tg ~ 30 °C)177,178 or high Tg such as 83 (Ref.179) are currently investigated as hole transporting materials (Table 5). All molecules 81–86 shown in Figure 17 bear relatively weak acceptor (preferably aromatic hydrocarbon) and highly twisted -linker. Further compounds 84 (Ref.180), 85 (Ref.61) and 86 (Ref.181) showed mixed hole-transporting and electroluminescent properties potentially applicable in advanced OLED color tuning. 36

Figure 17. Selected TPA-based hole-transporting materials 81–86. Table 5. Basic optical and hole transporting properties of compounds 81–86.

h

max

Tg/Tm/Td

[cm .V .s ]

[nm]

[°C]

81

-

383

81/241/-

220

-

Ref.

174

82

0.013

361

30/-/-

-

2.97

Ref.

177

83

-

410

202/-/-

-

3.1

Ref.

179

84

-

381

174/316/565

-

2.76

Ref.

180

85

-

360

-

1190

-

Ref.

86

-

338

69/374/-

480

3.28

Ref.

Comp.

2

2.2.4.2

-1

-1

ox

E

[mV]

opt

Eg

[eV]

References

61

181

Electroluminescent and electrochomic compounds

The voltage or electric current dependence of the UV/VIS light absorbance and absorption

maxima

(electrochromism)

and

voltage

dependent

light

emission

(electrolumeniscence, EL) are two tightly connected phenomena with a large scale of potential industrial application.182 The invention of OLED technology183 as well as the technology of smart glasses enhanced the research of polymeric as well as small organic molecules as promising materials for such applications. The tripodal molecules represent undoubtedly an important sub-group of such materials. Except of the quantum (non)linear optical properties of such materials (see the chapters 3.1–3.3), they also possess unique property of Förster-type incoherent energy migration among the branches. This migration was for instance studied on model compounds 87 and 88 (Figure 18).56,184 An occurrence of this phenomena in a molecule has immense impact on its polarizability as well as on the number 37

of allowed or magnetically and electrically inducible electron levels, which is the fundamental physical property of the electrochromism and electroluminescence. Branched and especially tripodal materials such as tris(8-hydroquinolato)aluminium (abbreviated as Alq3),185 have been applied in both electroluminescent and electrochromic devices even before the proper description of the aforementioned electronic properties. The Alq3, a typical example of A-(-D)3 system, represents a benchmark molecule currently used in majority of the multilayered OLED and PLED devices. Along with Alq3, large molecular (dendrimeric or polymeric) carbazole-186 and diphenyl-based187 D-(-D)n and (D--D)n molecules are routinely found as electrochromophores and electroluminophores in various devices. It has also been shown that molecule 89 (Figure 18), used as a polymeric precursor, possesses promising electroluminescent properties (λAmax (THF) = 420 nm, λE (THF) =489 nm,  (THF) = 0,73) but most of the current electroluminescent devices do not involve polymeres.64 Electroluminescent properties were also encountered for D-(-A)3 system 90 with benzothiadiazole rings appended to TPA core, which was further chemically bound to polyfluorene macromolecules.188,189

Figure 18. Selected examples of electrochromic D-(-A)3 molecules 87–90.

Tripodal D-(-A)3 TPA-based chromophores have recently been proven to be important grade-layer materials in multilayered OLED devices. Blue emitters such as 91 38

(Ref.190,191), 92 (Ref.192,193) and 93 (Ref.194), and some of their isomers structurally close to aforementioned hole transporting compounds 83 and 84 (Figure 17), along with pyrimidin-4yl substituted TPA derivative 94 (Ref.195) are selected examples of D-(-A)3 molecules representing inexpensive light emitting materials for multilayered electrochomic devices. Selected important properties of compounds 91–94 are summarized in Table 6. As can be seen, a red-shift of the longest-wavelength absorption maxima accompany enlargement of the -system (e.g. 92 vs. 91) as well as attaching electron withdrawing pyrimidine moiety (94). Surprisingly, less-extended derivative 92 showed bathochromically shifted electroluminescent maxima when compared to 91. The band gap decreases significantly with planarization of the system (91 vs. 93) as well as with improving ICT (94). Hence, the largest band gap and maximal luminance were recorded for the most twisted molecule 91.

Figure 19. Electroluminescent TPA materials 91–94. Table 6. EL properties of compounds 91–94.

Comp.

max (solvent) [nm]

EL (voltage) [nm]

Lmax -2

Eg

[cd m ]

[eV]

References

91

388 (CHCl3)

468 (5 V)

24 910

3.34

Ref.

191

92

365 (CHCl3)

528 (2.6 V)

7956

-

Ref.

192

93

365 (CHCl3)

-

-

3.02

Ref.

194

94

384 (CH2Cl2)

-

-

2.93

Ref.

194

Tripodal D-(-A)3 electrochromic emitters have recently also infiltrated near infrared emitting OLED devices that turned out to be of high interest in military sector and biomedicine imaging. Figure 20 shows such two selected examples - double-cored D-(-A)3 system 95 (Ref.196,197) chelating rhenium via central bipy pocket and push-pull molecule 96 (Ref.41) with peripheral anthraquinone acceptors.

39

Aggregation induced emission (AIE), the first step to achieve piezochromism, was also observed in relatively simple triphenylethenylphenyl-TPA derivatives 97 (Figure 20),198 that were thoroughly studied mainly for their electroluminescence.

Figure 20. Near IR electrochromic dyes 95–96 and AIE active molecule 97.

2.2.4.3 Photovoltaic applications TPA-derived push-pull molecules appeared in photovoltaic devices already in the mid 1980’s,19 and, therefore, photovoltaics can be considered as one of the oldest materials application of tripodal molecules. D-(-A)3 molecules can be found either as p- or n-type semiconducting materials in junction type solar cells (JTSC)199 or as sensitizers in dyesensitized solar cells (DSSC).200 Hence, in the subsequent two paragraphs, both types of devices and especially TPA-derived push-pull molecules with such prospective applications will be discussed. A general design of tripodal JTSC active TPA derivatives is not far from the design of multiphoton absorbing molecules (see above) - triphenylamine or structurally similar cores are linked to strong electron withdrawing peripheral moieties. Compound 98 (Figure 21)55 would represent one of such examples, surprisingly patented as late as 2013.

40

Figure 21. A typical example of push-pull TPA derivative used in JTSC.

Parent TPA connected to a strong electron withdrawing group via thiophene40,199,201 or oligothiophene35,202,203 -linkers proved to be very successful donors both in bi- and monolayered JTSCs and bulk-heterojunction devices (often mixed with soluble fullerene derivatives as acceptors). In these systems, a clearly distinguishable structure-activity relationship has been observed.204 Increasing the acceptor strength clearly reduces the band gap and enhances the photovoltaic characteristics. An addition of more electron withdrawing groups considerably decreases the band gap as well as indistinctly influences the energy conversion efficiency as can be seen on a series of compounds 99–102 (Figure 22, Table 7). On the other hand, an extension of the -linker is believed to decrease the band gap and enhances the efficiency.205 However, on the series of compounds 103a–103c bearing systematically extended oligothiophene -linker terminated with perylene-based acceptor (Figure 23, Table 7) such trends are hardly to be seen. In general, symmetric arrangement of tripodal systems is preferred over the asymmetric ones due to considerably lower anisotropy of the electronic properties. A comparison of two triphenylamine-based compounds (104a and 104b; Figure 24, Table 7) clearly shows that the efficiency was significantly enhanced when going from linear to tripodal systems.206 It should also be noted here that increasing the acceptor strength as well as the -linker length is usually accompanied by the extension of the chromophore effective absorption area within the available visible light spectrum.199,201

41

Figure 22. Variation of the peripheral electron acceptor as property tuning tool of TPA derivatives for solar cells. Table 7. Property trends in tripodal OSC active chromophores 98–104. Comp.

maxA (solvent) [nm]

Eg [eV]



Construction

Voc [V]

[%]

References 55

98

460 (CHCl3)

-

-

-

-

Ref.

99

509 (CH2Cl2)

1.78

bilayer D-C60

0.96

1.02

Ref.

201

100

528 (CH2Cl2)

2.02

-

-

-

Ref.

204

101

557 (CH2Cl2)

2.00

-

-

-

Ref.

204

102

613 (CH2Cl2)

1.75

-

-

-

Ref.

204

103a

520 (CHCl3)

2.11

-

-

-

Ref.

103b

490 (CHCl3)

2.11

BHJSC/PCBM

0.60

0.25

Ref.

35

103c

485 (CHCl3)

2.11

-

-

-

Ref.

35

104a

522 (PhCl)

1.86

BHJSC/PCBM

0.84

0.39

Ref.

206

104b

541 (PhCl)

2.00

BHJSC/PCBM

0.81

1.33

Ref.

206

42

35

Figure 23. TPA push-pull molecules 103 with perylene-based acceptor and systematically extended oligothiophene -linker.

Figure 24. Different arrangement of chromophore 104 as a tool to tune BHJSC efficiency.

Nowadays, design of tripodal molecules used in heterojunction solar cells (HJSC) is very burgeoning area. Figure 25 shows some recent examples of D-(-A)3 and D-(-A--D)3 systems 105 and 106. In 105, diketopyrrolopyrrole (DPP) has been linked to TPA via thiophene unit,203,207 which resulted in low band gap characteristics.208 In compound 106, TPA is substituted with benzothiadiazole acceptors end-capped with tri-thiophene auxiliary donor.209 This D-(-A--D)3 arrangement accounts for improved BHJSC efficiency up to 4.16 % (Table 8) recorded in the device fabricated with similar but planarized and extended molecule 108 (Ref.210,211). Noteworthy, a similar system linked to polymer backbone showed much worse performance.77 Extension of 106 and 108 by an additional terminal acceptor afforded D-(-A--D--A)3 molecule 107.42 However, this design led only to extraordinary spectral photovoltaic coverage (300–800 nm). 43

Data shown in Table 8 clearly demonstrates that, besides the strength of the acceptor and length of the -linker, the overall planarity of the molecule plays very important role. Planar system such as 108 possesses low open-circuit voltage and generally better efficiency. The -system can be planarized either by bridging the TPA core (108) or by attaching the peripheral acceptors via multiple bonds or five membered spacers (thiophene). Whereas the effect of an additional acceptor as in 107 is diminished, attachment of an additional auxiliary donor such as trithiophene in 106 and 108 led to significantly improved efficiency exceeding 4 %.

Figure 25. Recent TPA-derived push-pull molecules for HJSC. Table 8. Selected data showing performance of OSC compounds 105–109. Comp.

maxA (solvent) [nm]

Eg [eV]

Construction

Voc [V]

 [%]

References

105

596 (CHCl3)

1.56

BJHSC/P3HT

1.00

1.20

Ref.

203,207

106

512 (CHCl3)

1.90

BHJSC/PC71BM

0.96

4.17

Ref.

209,201

107

530 (CHCl3)

1.97

BHJSC/PC70BM

0.87

1.79

Ref.

108

590 (PhCl)

-

BHJSC/PC70BM

0.74

4.16

Ref.

204

109

430 (CH2Cl2)

2.68

-

-

-

Ref.

212

44

42

TPA molecules bearing terminal acetylene moiety were also applied in construction of organometallic molecules with ruthenium213,214 or rhenium.215 Such molecules were generally screened for their interesting redox propeties214 and NLO behavior.216 However, similar Pt(II)-complex 109 (Figure 26)212,217 and whereon build polymers proved to be interesting materials for high-voltage BHJSC (Table 8).

Figure 26. Organometallic TPA derivative 109 intended for BHJSC.

The invention of dye-sensitized solar cells (DSSCs)218 in 1991 opened a new application sphere where tripodal push-pull molecules could be involved. In contrast to JTSC technology, dyes used in DSSCs do not require any symmetry and tripodal molecules can be considered as disfavored to linear ones or organometallic dyes due to their tedious synthesis. On the other hand, in order to achieve good electron transport from the dye to TiO2 or NiO nano-particles,219 start-shaped push-pull molecules may have some advantage. In general, tripodal arrangement may adopt almost all currently developed DSSC-active dyes such as Grätzel’s original bipyridine ruthenium (II) complex.218,220 Such approach can be for instance demonstrated on recently published dye 110 (Figure 27)220 intended for Ru(II) chelation. However, this concept is rather an exception.

Figure 27. TPA equipped with terpyridine chelating auxiliary and two anchoring carboxylic groups.

45

Inspired by the chlorophyll, some organometallic sensitizers utilize porphyrine scaffold. Besides linear porphyrine-substituted TPA derivatives,221,222 tripodal molecules with multiporphyrine cores performed well in DSSCs. TPA based bis(zinc(II)porphyrin) with carboxylic anchoring moiety 111 along with tripodal system 112 (Figure 28)223 were very recently reported as dye sensitizers. The DSSC voltage about 0.6 V and power conversion efficiency not overcoming 0.31 % put these molecules as averagely successful compounds comparing with those shown in Table 8. Molecule 112 has also been tested in BHJSCs achieving the performance far from the aforementioned TPA derivatives shown in Table 7 and 8.224

Figure 28. Porphyrine-derived TPA molecules for DSSCs.

Another group of currently well investigated tripodal sensitizers evolved from common organic push-pull molecules. A general feature of all organic DSSCs active molecules is the presence of an anchoring group assuring electron transport from the dye to TiO2. These groups most often involve carboxylic acid, hydroxy group, pyridine or halogen.225–227 Figure 29 shows selected examples of D-(-A)3 systems bearing such anchoring moieties - 113 (Ref.228), 114 (Ref.229) and 115 (Ref.226). Table 9 summarizes their basic photovoltaic data and performance in DSSC. Comparing the values given in Table 9, however, is not very simple task as the DSSC performances are dependent on the detailed construction of the devices. For example initial very low values found for compound 114 are believed to allow an upgrade up to  ~ 28 %.229 Anyway, despite different device architecture, structurally developed sensitizers 113, 116 (Ref.230) and 117 allow some elucidation of the structure-property relationships. These molecules possess very similar absorption properties as well as band gaps. However, the latter two are equipped with three instead of one anchoring group. This structural change resulted in higher open-circuit voltage as well as significant improvement of the DSSC device efficiency up to 6.75 %. Hence, the structure (COOH vs. cyanoacrylic moieties), the number (1 vs. 3) and position of the anchoring group most likely play the most crucial role. In addition, extension of the -system 46

by thienylene units (116 vs. 117) brings another beneficial effect to the overall efficiency (3.30 vs. 6.75 %, Table 9). In contrast to the recent report of Meng et al., 231 these observation are directed towards his empirical findings that asymmetric branched push-pull molecules showed better performance than symmetric D-(-A)3 systems. Besides aforementioned common D-(-A)3 systems, variety of TPA-based or crosslinked232 light-absorbing molecules having extraordinary designs such as D--D-(-A)2 or (D--)2-D--A were developed to date.233,234

Figure 29. Selected examples of organic DSSC active molecules with various anchoring groups. Table 9. DSSC characteristics of sensitizers 113–117. Comp.

maxA (solvent) [nm]



Eg [eV]

DSSC nanoparticles

Voc [V]

[%]

References 228

113

464 (CH3CN)

2.24

NiO

0.122

0.113

114

536 (CH3CN)

2.27

NiO

0.079

0.08

115

490 (CH2Cl2)

-

NiO

0.130

0.14

Ref.

226

116

448 (DMSO)

2.46

TiO2

0.390

3.30

Ref.

230

117

484 (CHCl3)

2.24

TiO2

0.640

6.75

Ref.

235

47

Ref. Ref.

229,201

2.2.4.4 Electromagnetic applications Electromagnetic materials belong to another interesting application of tripodal push-pull systems. These molecules, whose structure is not far from the aforementioned photovoltaic, hole-transporting or electroluminescent compounds, were mostly applied as xerography photoreceptors. In this field, TPA-derivatives bearing “stable” radical groups on the periphery have been known for a long time.236 For instance, Eastmann Kodak Company has patented compound 118 with rhodanine acceptor units (Figure 30) already in 1973.237 This molecule was used as xerography photoreceptor and may be denoted as one of the very first D-(-A)2 systems based on TPA parent scaffold.

Figure 30. Xerography photoreceptor builds on TPA.

A paramagnetic behavior of D-(-A)3 systems has also been encountered, for example in tripodal transition metal acetylides such as 109 (Figure 26) or iron(III)-based analogues.238 Fully organic D-(-A)3 or D-(-A--D)3 molecules such as 119 and 120 (Figure 31) bearing strong acceptor units such as tetracyanobutadiene and benzoquinone-extended analogues proved to be significantly negatively charged on the periphery. 239,31 These molecules are capable of facile one-electron oxidation or reduction and were claimed as tripodal push-pull systems with prospective paramagnetic applications.

Figure 31. Highly charged push-pull molecules capable of one-electron oxidation.

48

2.3 2.3.1

Other applications of tripodal push-pull systems Analytical technologies

Beside (ir)reversible switching of chemical properties (see above), tripodal push-pull molecules were also used as chemical detectors. In contrast to others, tripodal systems have significant advantage of threefold binding/reaction sites located on the periphery. Hence, a wide variety of tripodal D-(-A)3 chemo-detectors have been developed to date. In principle, a coordination of an electrophile (a metal) by a push-pull molecule finely changes its ICT which results in a change in color, electrochemical behavior and other properties. The most common are detectors capable of distinguishing various cations such as mercury(II),240 copper149,241 or iron.242 Hydrazone and terpyridine TPA derivatives 121 (Ref.149) and 122 (Ref.242) bearing well-designed binding pockets are shown in Figure 32. Whereas 121 has primarily been used as copper(II)-sensitive luminescent detector, 122 detects iron ions.

Figure 32. Metal-binding detectors 121 and 122 as well as detectors of amines and polynitro explosives 123– 124 and 125–126.

Beside chelation of metals, well-substituted TPA derivatives such as 123 and 124 have also been used to detect aliphatic amines by a chemical reaction243 or anilines by generation of an intermolecular charge transfer complexes (Figure 32).244 Molecules 125 (Ref.26) and 126 (Ref.245), structurally similar to aforementioned electroluminescent and hole-transporting molecules, were found to detect traces of polynitro explosives (Figure 32).

49

Scheme 18. ICT quench in molecule 127a via nucleophilic addition of cyanide ions.

An interesting example of anion detection is shown in Scheme 18. Compound 127a bearing DCV acceptor proved to detect low concentration of cyanide anion via mechanism proposed in Scheme 18 and can be used even in cellula applications.246 Whereas 127a possesses efficient ICT/fluorescence, in 127b has been the DCV acceptor terminated and, therefore, the molecule is non-fluorescent. Similar systems were also developed for in vivo or in cellula detection of cysteine.247,248 2.3.2

Biological and medicinal applications Along with the development of nonlinear optics, new methods in biological imaging249

and medicinal therapy110 using 2PA or mutiphoton absorption recently appeared. D-(-A)3 systems with octupolar architecture with pronounced NLO response are mainly involved in such techniques.115 Beside compounds 68 (Figure 12),52 TPA derivatives 128 and 129 (Figure 33)44 have been used as materials for bio-imaging, which utilizes two-photon fluorescence imaging (TPFI). For 128, this bio-imaging can be performed even in living cells. Glycosylated analogue 129 (Ref.250) allows early diagnostics of neoplasms using TPFI.

50

Figure 33. TPA materials used for bio-imaging in living cells using TPFI technique.

TPA derivative 130 (Figure 34) bearing three peripheral carborane-vinyl groups has been utilized as fluorophore for fluorescence microscopy imaging (FMI).251

Figure 34. Fluorophore 130 used in FMI technique.

Coordination properties of pyridium,80 benzimidazolium,252 pyrazinium and pyrimidinium253 salts towards DNA allow compounds 131 and 132 (Figure 35) to act as DNA or particular DNA fragment binding fluorophores. Tripodal pyridinium and benthiazolinium salts such as 133 (Figure 35)254 have been used as a DNA-sensitizers for two photon microscopy. In addition, D-(-A)3 systems based on pyridine with two TPA cores are proved to behave as a three-photon induced green emitters and thus are very promising molecules for 3PA imaging.255

51

Figure 35. DNA staining tripodal push-pull molecules.

Benzimidazolium linked via oxazole to TPA core afforded tripodal system 134 (Figure 36).256 This molecule showed infrared light apoptosis induction which can be considered as a notable property for future prospective therapeutic applications.

Figure 36. IR apoptosis inducer 134.

Even though the photodynamic therapy (PDT) has routinely been used for a decade, there are still new methodologies to be explored. The porphyrine-based tripodal systems seem to be advantageous for such purposes.257 Asymmetric pyridine-porphyrine TPA derivative 135 (Ref.258) along with symmetric trisporphyrine molecule 136 (Figure 37)259 belong to a family of tripodal push-pull molecules considered as red or near-IR light responding sensitizers. Moreover, these molecules may be, upon glycosylation, also tissue targeted.

52

Figure 37. Porphyrine-derived TPA molecules 135 and 136 applicable in PDT.

53

3 Experimental part 3.1

General methods

THF was dried in Puresolv™ micro solvent purification system. All commercial chemicals and solvents along with chromophore 149 were purchased from suppliers such as Sigma Aldrich, Acros and TCI at reagent grade quality and were used as obtained. All crosscoupling reactions were carried out in flame-dried flasks under argon, if not described otherwise. Thin-layer chromatography (TLC) was conducted on aluminum sheets coated with silica gel 60 F254 with visualization by a UV lamp (254 or 365 nm). 1H and 13C NMR spectra were recorded at 400 and 100 MHz, respectively, with a Bruker AVANCE 400 instrument, or at 500 and 125 MHz with Bruker Ascend™ 500, respectively. Chemical shifts in 1H,

13

C

spectra are reported in ppm relative to the signal of Me4Si. The residual solvent signal in the 1

H and

13

C-NMR spectra was used as an internal reference (CDCl3 7.25 and 77.23 ppm,

CD2Cl2 5.32 and 54.00 ppm and d6-DMSO 2.55 and 39.51 ppm). Apparent resonance multiplicities are described as s (singlet), d (doublet), t (triplet) and m (multiplet), apparent coupling constants of multiplets (3J or 4J) are given in Hz. IR spectra were recorded as neat using HATR adapter on a Perkin-Elmer FTIR Spectrum BX spectrometer. EI-MS spectra were measured on a GC/MS configuration comprised of an Agilent Technologies 6890N gas chromatograph equipped with a 5973 Network MS detector (EI 70 eV, mass range 33–550 Da). High resolution MALDI MS spectra were measured on a MALDI mass spectrometer LTQ Orbitrap XL (Thermo Fisher Scientific, Bremen, Germany) equipped with nitrogen UV laser (337 nm, 60 Hz). The LTQ Orbitrap instrument was operated in positive- or negative-ion mode over a normal mass range (m/z 50 – 2000) with resolution 100 000 at m/z = 400. The survey crystal positioning system (survey CPS) was set for the random choice of shot position by automatic crystal recognition. The used matrices were 2,5-dihydroxybenzoic acid (DHB) or 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB). Mass spectra were averaged over the whole MS record for all measured samples. Thermal properties of target molecules were measured by DSC with a Mettler-Toledo STARe System DSC 2/700 equipped with FRS 6 ceramic sensor and cooling system HUBERT TC100-MT RC 23. Melting points of intermediates were measured in open capillaries and were uncorrected.

54

3.2

General

procedure

for

the

Suzuki-Miyaura

cross-coupling

(139, 141(ql), 155) Suitable iodo-triphenylamine (0.24 mmol) and suitable boronic (0.90, 0.60 or 0.30 mmol) were dissolved in a mixture of THF and water (30 ml, 4:1). Argon was bubbled through the mixture for 10 min, whereupon Na2CO3 (106 mg, 1 mmol) and PdCl2(PPh3)2 or Pd(PPh3)4 (0.024 mmol) were added and the mixture was refluxed for 8 h. The reaction was quenched with saturated NH4Cl aq. solution (100 ml) and was extracted with DCM (3×100 ml). The combined organic extracts were dried over anhydrous Na2SO4 and concentrated in vacuo.

3.3

General

method

for

the

Sonogashira

cross-coupling

(140(ql), 166, 167) Suitable iodo-triphenylamine (0.24 mmol) and suitable terminal acetylene (0.90, 0.60 or 0.30 mmol) were dissolved in dry THF (15 ml). TEA (5 ml, 36 mmol) was added and subsequently argon was bubbled through the mixture for 10 min, whereupon PdCl2(PPh3)2 (16 mg, 0.024 mmol) and CuI (13 mg, 0.069 mmol) were added. The reaction was heated to 70 °C for 8 h. The reaction mixture was poured into the saturated NH4Cl solution (100 ml) and was extracted with DCM (3×100 ml). The combined organic extracts were dried over anhydrous Na2SO4 and concentrated in vacuo.

3.4

General method for the optimized Sonogashira cross-coupling (145, 146, 147, 148)

Tris(4-ethynylphenyl)amine 8 (317 mg, 1.00 mmol) and the corresponding halogen derivative 163, 164, 173 or 177 (3.6 mmol) were dissolved in a mixture of dry 1,4-dioxane (40 ml) and TEA (10 ml, 71.8 mmol). Argon was bubbled through the mixture for 10 min, whereupon Pd(PPh3)4 (116 mg, 0.10 mmol) and CuI (38 mg, 0.2 mmol) were added and the reaction mixture was heated to 92 °C for 8 h. The reaction mixture was quenched with saturated solution of NH4Cl (150 ml) and was extracted with DCM (2×150 ml). The combined organic extracts were dried over anhydrous Na2SO4 and concentrated in vacuo.

55

3.5

General method for the Knoevenagel condensation (142, 143)

Suitable aldehyde 10 or 168 (0.5 mmol) and malononitrile 170 (150 mg, 2.27 mmol) were dissolved in DCM (20 ml) and alumina (930 mg, 8.9 mmol, Brockmann activity II–III) was added. The reaction mixture was stirred for 4 h and was monitored by TLC (SiO2, DCM/ EtOAc 10:1). Anhydrous Na2SO4 (350 mg, 2.46 mmol) could eventually be added to accelerate the reaction. The resulting colored suspension was filtered and the filtrate was concentrated in vacuo.

3.6

General method of the N-methylation of pyridine compounds (150, 152, 154, 156)

Suitable pyridine compound 149, 151, 153 or 155 (1 mmol) was dispersed in methylidodide (14.2 g, 100 mmol) and the resulting dispersion was stirred for 8 h. The product was filtered off and was washed by DCM (3×75 ml).

3.7

General method for preparation of carboxylic acids (157, 158, 159)

Oxidation of bromoxylenes and bromomesitylene was carried out according to modified

literature

procedure.260

The

appropriate

commercial

bromoxylene

or

bromomesitylene (20 mmol) was dissolved in tBuOH (15 ml) and water (15 ml) and the mixture was heated to 117 °C. Solid KMnO4 (40 mmol per each methyl group + 40 mmol excess) was added portionwise into the hot mixture during 2 h. The reaction mixture was heated to reflux for 10 h, cooled to 25 °C, whereupon formaldehyde (50 ml, 40% aq. solution) was added and the mixture was boiled again to degrade the residual KMnO4. Hot reaction mixture was filtered through a 5 cm plug of Celite® and the plug was subsequently washed with boiling water (3×100 ml). The combined opalescent filtrates were concentrated to one third of the original volume in vacuo. The pH was adjusted to 1-2 with HCl (35 %). The white precipitate formed was filtered off and the crude product was crystallized from water.

56

3.8

General method for preparation of amides (160, 161, 162)

Amides 160 – 162 were prepared according to modified literature procedure. 261 Well dried compounds 157–159 (10 mmol) were suspended in SOCl2 (40 ml, 206 mmol) and DMF (2 ml, 26 mmol) was added. The reaction mixture was heated to reflux for 4 h. SOCl2 was distilled off and the residue was dissolved in dry DCM (200 ml). Gaseous NH3 was bubbled through the solution for 2 h (apparent and spontaneous cooling of the reaction mixture usually indicated the end of the reaction). DCM was evaporated in vacuo and the crude product was recrystallized two or three times from water.

3.9

General method for preparation of nitriles (163, 164, 165)

Dehydratation of amides was carried out via a standard literature procedure.262 Amide 160–162 (3 mmol) was suspended in 1,4-dioxane (30 ml). Pyridine (3 ml, 37 mmol) was added and the reaction mixture was cooled to 0 °C. TFAA (6 mmol per each amide group) was added dropwise with cooling during 30 min and the mixture was allowed to reach 25 °C and was stirred for additional 2 h. The reaction pH was adjusted to 7–8 with saturated NaHCO3 solution and then extracted with DCM (3×50 ml). Combined organic extracts were dried over anhydrous Na2SO4 and concentrated in vacuo. The crude product was recrystallized from the mixture of diethyether and pet-ether.

3.10 Chromophore 137 Triphenylamine 4,4’,4’’-triscarboxaldyde 10 (200 mg, 0.61 mmol) was heated to reflux with NH3OH+Cl- (212 mg, 3.04 mmol) in 25 ml of DMF. After gaining the boiling point of the mixture, TFAA (384 mg, 1.83 mmol) was added dropwise and the resulting mixture was refluxed for 6 h. The reaction mixture was poured over ice/water and was extracted with DCM (3×100 ml). The combined organic extracts were washed with water (100 ml) and brine (2×100 ml), dried over anhydrous Na2SO4 and concentrated in vacuo. Column chromatography (SiO2; DCM/hexane 1:1) afforded 137. Off-white solid (90 mg, 46 %). Rf 0.75 (SiO2; DCM/Hexane 1:1). M. p. 343 °C (lit.263 340–342 °C). IR (HATR) max = 2921, 2214 (CN), 1589, 1496, 1270, 1177, 836 cm-1. 1

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.15 (d, 6H, 3J = 8.8 Hz, CHAr), 7.61 (d, 6H, 3J =

8.8 Hz, CHAr,) ppm.

13

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 108.3, 119.0, 125.5, 134.5,

149.9 ppm. HR-MALDI-MS (DHB): m/z calculated for C21H12N4 (M+) 320.1057 found 320.1059. 57

3.11 Chromophore 138 Compound 138 was prepared according to the literature264 starting from 6 (243 mg, 0.39 mmol) and acrolein 169 (250 l, 3.8 mmol). Purification by column chromatography afforded 138. Yellow solid (115 mg, 74 %). Rf 0.6 (SiO2; EtOAc/Hexane 1:3). M. p. 275 °C. IR (HATR) max = 2892, 2212 (CN), 1589, 1497, 1264, 1178, 964, 947, 808 cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 5.81 (d, 3H, 3J = 16.8 Hz, CH=CH), 7.09 (d, 6H, 3J = 8.4 Hz, NPhH), 7.35 (3 H, d, 3J = 16.8 Hz, =CH), 7.40 (6 H, d, 3J = 8.4 Hz, CHAr) ppm.

13

C-NMR (100 MHz, CD2Cl2, 25 °C): δC = 95.3, 118.5, 124.7, 129.1, 129.5, 148.8,

149.4 ppm. HR-MALDI-MS (DCTB): m/z calculated for C27H18N4 (M+) 398.1526 found 398.1528.

3.12 Chromophore 139 Title compound was from 6 (150 mg, 0.24 mmol) and 4-cyanophenylboronic acid (170, 132 mg, 0.90 mmol) prepared following the general procedure for the Suzuki-Miaura crosscoupling (Chapter 3.2). Purification of the crude product by column chromatography (SiO2; EtOAc/hexane 1:3) afforded 139. Yellowish solid. Yield (77 mg, 76 %). Rf 0.35 (SiO2; EtOAc/hexane 1:3). Mp 329 °C. IR (HATR): max = 3034, 2220 (CN), 1589, 1488, 1272, 1182, 820 cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.26 (d, 6H, 3J = 8.8 Hz, N-PhHPhCN), 7.59 (d, 6H, 3J = 8.8 Hz, N-PhH-PhCN), 7.70–7.75 (m, 12 H, N-Ph-PhH-CN) ppm. 13

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 111.1, 119.5, 125.2, 127.7, 128.8, 133.2, 134.5,

145.2 148.1 ppm. HR-MALDI-MS (DCTB): m/z calculated for C21H12N4 (M+) 320.1057 found 320.1059.

3.13 Chromophore 140 Title compound was synthesized from 6 (150 mg, 0.24 mmol) and 4-ethynylbenzonitrile (171, 127 mg, 0.90 mmol)

following

the

general

procedure

for

the

Sonoghashira cross-coupling (Chapter 3.3). Purifiaction of the crude product by column chromatography (SiO2; EtOAc/hexane 1 : 4) afforded 140. 58

Reddish solid. Rf 0.25 (SiO2; EtOAc/hexane 1 : 4). Yield 103 mg (69 %). M. p. 217 °C (lit.265 234 – 236 °C). IR (HATR) max = 2921, 2216 (CN), 1587, 1486, 1260, 1067, 1021, 806 cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.09 (d, 6H, 3J = 8.8 Hz, NPhH-PhCN), 7.45 (d, 6H, 3J = 8.8 Hz, NPhH-PhCN), 7.57 (d, 6H, 3J = 8.4 Hz, NPh-PhHCN), 7.62 (d, 6H, 3

J = 8.4 Hz, NPh-PhHCN) ppm. 13C-NMR (100 MHz, CD2Cl2, 25 °C): δC = 88.1, 93.8, 111.5,

117.4, 118.7, 124.3, 128.4, 132.1, 132.2, 133.3, 147.3 ppm. HR-MALDI-MS (DHB): m/z calculated for C45H24N4 (M+) 620.1996 found 620.2003.

3.14 Chromophore 140q Title

compound

was

synthesized

from

4,4’-diiodotriphenylamine 179 (123 mg, 0.24 mmol) and 171 (85 mg, 0.6 mmol) following the general procedure for the Sonogashira crosscoupling (Chapter 3.3). Purification of the crude product by column chromatography (SiO2; EtOAc/Hexane 1 : 4) afforded 140q. Chicken yellow solid. Yield 91 mg (80 %). Rf 0.65 (SiO2; EtOAc/Hexane 1 : 4). Mp 232 °C. IR (HATR) max = 2206 (CN), 1585, 1485, 1269, 1110, 1021, 830 cm-1. 1H-NMR (500 MHz, CD2Cl2, 25 °C): δH = 7.06 (d, 4H, 3J = 9.0 Hz, N-PhHAr), 7.15 – 7.19 (m, 3H, N-PhH), 7.34 (t, 3H, 3J = 7.0 Hz, N-PhH), 7.43 (d, 4H, 3J = 9.0 Hz, N-PhH-Ar), 7.59 (d, 4H, Ph-PhH-CN) ppm.

13

3

J = 8.6 Hz, Ph-PhH-CN), 7.62 (d, 4H,

3

J = 8.6 Hz,

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 88.0, 94.3, 111.7, 116.14,

119.1, 123.6, 125.4, 126.6, 128.8, 130.2, 132.3, 132.6, 133.4, 146.8, 148.4 ppm. HR-FT-MALDI-MS (DHB): m/z calculated for C36H21N3 (M+) 495.17355 found 495.17365.

3.15 Chromophore 140l Title compound was synthesized from 4-iodotriphenylamine 178 (89 mg, 0.24 mmol) and 171 (43 mg, 0.30 mmol) following the general procedure for the Sonogashira cross-coupling (Chapter 3.3). Purification of the crude product by column chromatography (SiO2; EtOAc/Hexane 1 : 4) afforded 140l. Pale yellow solid. Yield 80 mg (94 %). Rf 0.7 (SiO2; EtOAc/Hexane 1 : 4). M. p. 101 °C (lit266 159 °C). IR (HATR) max = 3030, 2212 (CN), 1578, 1486, 1266, 1176, 1073, 755, 694 cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.01 (d, 2H, 3

J = 8.8 Hz, N-PhH-Ar), 7.12 – 7.16 (m, 6H, N-PhH), 7.32 (t, 4H, 3J = 7.6 Hz, N-PhH), 7.40

(d, 4H, 3J = 8.8 Hz, N-PhH-Ar), 7.60 (d, 2H, 3J = 8.4 Hz, Ph-PhH-CN), 7.65 (d, 4H, 3

J = 8.4 Hz, Ph-PhH-CN) ppm. 13C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 87.6, 94.7, 111.5, 59

114.8, 119.1, 121.9, 124.5, 125.9, 129.0, 130.0, 132.3, 132.6, 133.2, 147.4, 149.3 ppm. HR-FT-MALDI-MS (DHB): m/z calculated for C27H18N2 (M+) 370.14645 found 370.14592.

3.16 Chromophore 141 Title compound was synthesized from 6 (150 mg, 0.24 mmol) and 2-(4-cyanophenyl)vinylboronic acid pinacol ester (175, 230 mg, 0.90 mmol) following the general procedure for the Suzuki-Miyaura cross-coupling (Chapter 3.2). Purification of the crude product by column chromatography (SiO2; EtOAc/Hexane 1 : 4) afforded 141. Greenish yellow solid. Yield 100 mg (76 %). Rf 0.4 (SiO2; EtOAc/Hexane 1:4). Mp 291 °C (lit.118 148 °C) IR (HATR) max = 2920, 2219 (CN), 1589, 1505, 1277, 1172, 960, 831 cm-1. 1

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.05 (d, 3H, 3J = 16.4 Hz, CH=CH), 7.13 (d, 6H,

3

J = 8.4 Hz, N-PhH), 7.22 (d, 3H, 3J = 16.4 Hz, CH=CH), 7.48 (d, 6H, 3J = 8.8 Hz, CHAr),

7.61 (q, 12H, 3J = 8.8 Hz, CHAr) ppm.

13

C-NMR (100 MHz, CD2Cl2, 25 °C): δC = 88.1, 93.8,

111.5, 117.4, 118.7, 124.3, 128.4, 132.1, 132.2, 133.3, 147.3 ppm. HR-MALDI-MS (DHB): m/z calculated for C45H30N4 (M+) 626.2471 found 626.2474.

3.17 Chromophore 141q Title compound was synthesized from 179 (123 mg, 0.24 mmol) and 175 (153 mg, 0.60 mmol) following the general procedure for the Suzuki-Miyaura cross-coupling (Chapter 3.2). Purification of the crude product by column chromatography (SiO2; EtOAc/Hexane 1 : 4) afforded 141q. Yellow solid. Yield 139 mg (82 %). Rf 0.55 (SiO2; EtOAc/Hexane 1:4). M. p. 203 °C. IR (HATR) max = 3180, 2221 (CN), 1585, 1484, 1276, 1171, 958, 831 cm-1. 1

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.02 (d, 2H, 3J = 16.4 Hz, Ph-CH=CH-PhCN),

7.08 (d, 4H, 3J = 8.8 Hz, N-PhH-CH=CH), 7.12–7.15 3

(m, 3H, N-PhH), 7.17 (d, 2H,

3

J = 16.4 Hz, Ph-CH=CH-PhCN), 7.31 (t, 3H, J = 7.0 Hz, N-PhH), 7.43 (d, 4H, 3J = 9.0 Hz,

N-PhH-Ar), 7.59 (d, 4H, Ph-PhH-CN) ppm.

13

3

J = 8.6 Hz, Ph-PhH-CN), 7.62 (d, 4H,

3

J = 8.6 Hz,

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 88.0, 94.3, 111.7, 116.14,

119.1, 123.6, 125.4, 126.6, 128.8, 130.2, 132.3, 132.6, 133.4, 146.8, 148.4 ppm. HR-MALDI-MS (DHB): m/z calculated for C36H25N3 (M+) 499.20430 found 499.20466.

60

3.18 Chromophore 141l Title compound was synthesized from 178 (89 mg, 0.24 mmol) and 175 (77 mg, 0.30 mmol) following the general procedure for the Suzuki-Miyaura crosscoupling (Chapter 3.2). Purification of the crude product by column chromatography (SiO2; EtOAc/Hexane 1 : 4) afforded 141l. Yellow solid. Yield 119 mg (94 %), Rf 0.5 (SiO2; EtOAc/Hexane 1:4). M. p. 131 °C. 1

IR (HATR) max = 2223 (CN), 1583, 1484, 1276, 1168, 968, 824 cm-1.

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.02 (d, 2H, 3J = 16.4 Hz, Ph-CH=CH-PhCN),

7.08 (d, 4H, 3J = 8.8 Hz, N-PhH-CH=CH), 7.12 – 7.15 (m, 3H, N-PhH), 7.17 (d, 2H, 3

J = 16.4 Hz, Ph-CH=CH-PhCN), 7.31 (t, 3H, 3J = 7.0 Hz, N-PhH), 7.43 (d, 4H, 3J = 9.0 Hz,

N-PhH-Ar), 7.59 (d, 4H, 3J = 8.6, Ph-PhH-CN), 7.62 (d, 4H, 3J = 8.6, Ph-PhH-CN) ppm. 13

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 88.0, 94.3, 111.7, 116.14, 119.1, 123.6, 125.4,

126.6, 128.8, 130.2, 132.3, 132.6, 133.4, 146.8, 148.4 ppm. HR-MALDI-MS (DHB): m/z calculated for C36H25N3 (M+) 499.20430 found 499.20466.

3.19 Chromophore 142 The title compound was synthesized from triphenylamine-4,4’,4’’carboxaldehyde (10, 155 mg, 0.5 mmol) and malononitrile (150 mg, 2.3 mmol) following the general procedure for the Knoevenagel condensation (Chapter 0). Purification of the crude product by column chromatography (SiO2; DCM/EtOAc 10 : 1) afforded 142. Reddish-orange solid. Yield 122 mg (42 %). Rf 0.3 (SiO2; DCM/EtOAc 10 : 1). Mp 145 °C (lit.121 180 °C). IR (HATR) max = 3087, 2220 (CN), 1559, 1496, 1269, 1186, 827 cm-1. 1

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.25 (6H, d, 3J = 8.8 Hz, N-PhH), 7.73 (s, 3H,

CH=C(CN)2), 7.90 (d, 6H, 3J = 8.8 Hz, N-PhH) ppm. 13C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 81.6, 113.6, 114.7, 125.4, 128.2, 133.3, 150.7, 158.5 ppm. HRMALDI-MS (DHB): m/z calculated for C30H15N7 (M+) 473.1384 found 473.1385.

61

3.20 Chromophore 143 The title compound was synthesized from 168 (200 mg, 0.5 mmol) and malononitrile (150 mg, 2.3 mmol) following the general procedure for the Knoevenagel condensation (Chapter 0). Purification of the crude product by column chromatography (SiO2; DCM) afforded 143. Dark red solid. Yield 256 mg (94 %). Rf = 0.35 (SiO2; DCM). M. p. 84 °C. IR (HATR) max = 3010, 2216 (CN), 1539, 1495, 1316, 1266, 1176, 1026, 832 cm-1. 1H-NMR: H (400 MHz; CD2Cl2) 7.14 (d, 6H, 3J = 9.0 Hz, NPhH), 7.36 (s, 3H, CH=C(CN)2), 7.56 (d, 6H, 3J = 9.0 Hz, CHAr) ppm.

13

C-NMR (100 MHz, CD2Cl2, 25 °C):

δC = 86.2, 93.0, 111.4, 112.47, 114.9, 115.6, 124.5, 135.0, 140.8, 148.5 ppm. HR-MALDI-MS (DHB): m/z calculated for C36H15N7 (M+) 545.1384 found 545.1386.

3.21 Chromophore 144 4,4’,4’’-Triiodotriphenylamine 6 (300 mg, 0.48 mmol) and 1-methyl-2-vinyl-1H-imidazole-4,5-dicarbonitrile (176, 236 mg, 1.49 mmol) were dissolved in dry DMF (5 ml) and DIPEA (1 ml, 5.75 mmol). Argon was bubbled through the mixture for 10 min, whereupon Pd(PtBu3)2 (20 mg, 0.04 mmol) was added and the reaction mixture was heated to 85 °C for 8 h. The reaction mixture was poured into saturated NH4Cl solution (100 ml) and was extracted with DCM (2×100 ml). The combined organic extracts were washed with brine (150 ml) and water (100 ml), dried over anhydrous Na2SO4 and concentrated in vacuo. The crude product was purified by column chromatography (SiO2, EtOAc/ hexane 1 : 3) to afford 144. Orange solid. Yield 144 mg, (42%). Rf 0.4 (SiO2; EtOAc/hexane 1 : 3). M. p. 188 °C. IR (HATR) max = 2294, 2231 (CN), 1592, 1506, 1324, 1285, 1179, 972, 818 cm-1. 1

H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 3.83 (s, 9H, CH3), 6.77 (d, 6H, 3J = 16.0 Hz,

CH=CH), 7.16 (d, 6H, 3J = 8.5 Hz, N-PhH), 7.54 (d, 6H, 3J = 8.5 Hz, N-PhH), 7.81 (d, 6H, 3

J = 16.0 Hz, CH=CH) ppm. 13C-NMR (100 MHz, CD2Cl2, 25 °C): δC = (100 MHz; CD2Cl2)

33.2, 109.1, 109.5, 112.8, 113.3, 122.8, 125.0, 129.5, 130.9, 139.7, 148.6, 151.3 ppm. HR-MALDI-MS (DCTB): m/z calculated for C42H27N13 (M+) 713.2507 found 713.2526.

62

3.22 Chromophore 145 The title compound was synthesized from 8 (317 mg, 1 mmol) and 163 (745 mg, 3.6 mmol) following the general method for the optimized Sonogashira cross-coupling (Chapter 3.4). Purification of the crude product by column chromatography (SiO2; EtOAc/hexane 2 : 3) afforded 145. Dark yellow solid. Yield 204 mg (29 %). Rf 0.35 (SiO2; EtOAC/hexane 2 : 3). M. p. 327 °C (dec.). IR (HATR) max = 2921, 2206 (CN), 1593, 1504, 1320, 1289, 1145, 836, 801, 736 cm-1. δH = 7.19 (d, 6H, 7.64 (d, 6H,

3

3

1

H-NMR (400 MHz, CD2Cl2, 25 °C):

J = 8.8 Hz, NPhH), 7.52 (t, 3H,

J = 8.8 Hz, NPhH), 7.90 (d, 6H,

3

3

J = 8.0 Hz, Ph(CN)2H),

J = 8.0 Hz, Ph(CN)2H) ppm.

C-NMR (100 MHz; CD2Cl2): C = 83.4, 103.5, 116.2, 116.5, 124.5, 128.3, 131.2, 134.3,

13

136.4 148.1, 149.5 ppm. HR-MALDI-MS (DHB): m/z calculated for C48H21N7 (M+) 695.1853 found 695.1852.

3.23 Chromophore 146 The

title

compound

(317 mg, 1 mmol) following

the

and general

was 164

synthesized (745

method

mg, for

the

from 3.6

8

mmol)

optimized

Sonogashira cross-coupling (Chapter 3.4). Purification of the

crude

product

by

column

chromatography

(SiO2; EtOAC/hexane 2 : 3) afforded 146. Orange solid. Yield 144 mg (21 %). Rf 0.4 (SiO2; EtOAc/hexane 2 : 3). M. p. 282 °C (dec.). IR (HATR) max = 2922, 2204 (CN), 1593, 1503, 1320, 1277, 1145, 836, 800, 735cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.24 (d, 6H, 3

J = 8.8 Hz, NPhH), 7.66 (d, 6H, 3J = 8.8 Hz, NPhH), 7.81 (d, 3H, 3J = 8.4 Hz, PhH(CN)2),

7.92 (dd, 3H, 3J = 8.4 Hz, 4J = 1.2 Hz, PhH(CN)2), 8.04 (d, 3H, 4J = 1.2 Hz, PhH(CN)2) ppm. C-NMR (100 MHz; CD2Cl2): C = 85.7, 101.1, 112.5, 116.4, 116.7, 116.8,

13

117.2, 124.9, 132.0, 133.2, 134.3, 136.1, 136.5, 148.4 ppm. HR-MALDI-MS (DHB): m/z calculated for C48H21N7 (M+) 695.1853 found 695.1872.

63

3.24 Chromophore 147 The title compound was synthesized from 8 (317 mg, 1 mmol) and 5-bromothiophene-2-carbonitrile (173, 677 mg, 3.6 mmol) following the general method for the optimized Sonogashira cross-coupling (Chapter 3.4). Purification of the crude product by column chromatography (SiO2; EtOAC/hexane 3 : 4) afforded 147. Orange solid. Yield 160 mg (25 %). Rf 0.35 (SiO2; EtOAc/hexane 3 : 4). M. p. 191 °C. IR (HATR) max = 2925, 2208 (CN), 1593, 1504, 1320, 1291, 834, 808, 737 cm-1. 1H-NMR (400 MHz, CD2Cl2, 25 °C): δH = 7.18 (6H, d, 3J = 8.8 Hz, NPhH), 7.31 (3H, d, 3J = 4.0 Hz, ThH), 7.55 (6H, d, 3J = 8.8 Hz, NPhH), 7.62 (3H, d, 3

J = 4.0 Hz, ThH) ppm.

13

C-NMR (100 MHz, CD2Cl2, 25 °C): δC = 81.2, 97.0, 110.4,

114.1, 117.1, 124.8, 131.2, 132.0, 133.6, 138.0, 147.9 ppm. HR-MALDI-MS (DHB): m/z calculated for C39H18N4S3 (M+) 638.0688 found 638.0705.

3.25

Chromophore 148 The title compound was synthesized from 8 (317 mg, 1 mmol) and 2-iodo-thiophene-3,4-carbonitrile (177, 936 mg, 3.6 mmol) following

the

general

method

for

the

Sonogashira

cross-coupling (Chapter 3.4). Purification of the crude product by column chromatography (SiO2; EtOAC/hexane 3 : 4) afforded 148. Dark orange solid. Yield 111 mg (16 %). Rf 0.25 (SiO2; EtOAc/hexane 3 : 4). M. p. 198 °C (dec.). IR (HATR) max = 2848, 2236 (CN), 1592, 1472, 1377,

1169,

831, 3

728,

718

cm-1.

1

H-NMR

(500

MHz,

CD2Cl2,

25

°C):

3

δH =7.19 (6H, d, J = 9.0 Hz, CHAr), 7.59 (6H, d, J = 9.0 Hz, CHAr), 7.99 (3H, s, ThH) ppm. 13

C-NMR (125 MHz, CD2Cl2, 25 °C): δC = 78.2, 103.1, 111.8, 111.9, 112.3,

114.9, 115.8, 124.6, 133.7, 135.5, 136.6, 148.0 ppm. HR-MALDI-MS (DHB): m/z calculated for C42H27N13 (M+) 713.2507 found 713.2532.

64

3.26 Chromophore 150 The title compound was synthesized from 4-aminopyridine (149, 94 mg, 1 mmol) following the general method of N-methylation of pyridine compounds (Chapter 3.6). White solid. Yield 235 mg (> 99 %). IR (HATR) max = 3145, 1651, 1537, 1198, 825, 610 cm-1. M. p. 184–186 °C (lit.267 188–190 °C). 1H-NMR (500 MHz, d6-DMSO, 25 °C): δH = 3.90 (s, 2H, NCH3), 6.83 (d, 2H, 3J = 7.5 Hz, NPyH), 8.06 (br s, 2H, NH2), 8.14 (d, 2H, 3

J = 7.5 Hz, NPyH) ppm.

13

C-NMR (125 MHz, d6-DMSO, 25 °C): δC = 44.4, 109.3, 143.8,

158.4 ppm. HR-MALDI-MS (DHB): m/z calculated for C6H9N2 (M-I)+ 109.07602 found 109.07601.

3.27 Chromophore 151 Chromophore 151 was synthesized by modified literature procedure (Ref.268). To the solution of 149 (9.4 g, 0.1 mol) in PCl3 (9.2 ml, 0.105 mol) pyridine (17.8 ml, 0.22 mol) was added dropwise. The reaction mixture, sponateously heated to approximately 100 °C, was refluxed (at 140 °C) for 5 h. From the resulting thick orange supension all the liquids were distilled out to the dryness. Remaining solids were transferred into the mixture of EtOH (5 ml), water (50 ml) and HCl (35–37 %, 10 ml) and the resulting suspension was boiled (at 105 °C) for 1h. The precipitate was filtered off while hot and was washed with 20 % HCl (2×100 ml). The supernatant was cooled in the ice bath and neutralized with NaOH (1 M aqueous solution) to pH 9–10. The off-white precipitate was collected and washed with diethylether (2×50 ml) and water (2×50 ml). The crude product was purified by a short plug (SiO2; MeOH) or crystalized (EtOH/water 2 : 1). Pale white solid. Yield 7.6 g (44 %), M. p. 282–284 °C (lit268 273–275 °C). IR (HATR) max = 2668, 1574, 1485, 1343, 1205, 831, 998, 798 cm-1. 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 7.16 (d, 4H, 3J = 6.4 Hz, NPyH), 8.39 (d, 4H, 3J = 6.4 Hz, N-PyH), 9.39 (brs, 1H, NHPy).

13

C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 111.7, 147.8,

150.5 ppm. HR-MALDI-MS (DHB): m/z calculated for C10H9N3 (M+) 172.08692 found 172.08730.

3.28 Chromophore 152 The title compound was synthesized from 151 (173 mg, 1 mmol) following the general procedure for N-methylation of pyridine compounds (Chapter 3.6). White solid. Yield 235 mg (> 99 %). M. p. 184–186 °C. IR (HATR) max = 3145, 1651, 1537, 1198, 825, 610 cm-1. 1H-NMR (500 MHz, d6-DMSO, 25 °C): δH = 3.90 (s, 2H, NCH3), 6.83 65

(d, 2H, 3J = 7.5 Hz, CHAr), 8.06 (br s, 2H, NH2), 8.14 (d, 2H, 3J = 7.5 Hz, CHAr) ppm. 13

C-NMR (125 MHz, d6-DMSO, 25 °C): δC = 44.4, 109.3, 143.8, 158.4 ppm.

HR-MALDI-MS (DHB): m/z calculated for C12H15N3 ([M-HI]+) 200.11822 found 200.11822.

3.29 Chromophore 153 Chromophore 153 was synthesized analogically to known C-N cross-coupling (Ref.269). Compound 151 (514 mg, 3.0 mmol), 4-iodopyridine (615 mg, 3.0 mmol), CuBr (430 mg, 3.0 mmol) and Cs2CO3 (977 mg, 3.0 mmol) were dissolved in the NMP (30 ml) and argon was bubbled for 10 min. The reaction mixture was heated at 190 °C for 8 h, was poured over ice (400 ml) and aqeous ammonia (25–27 %; 50 ml) was added. The resulting mixture was extracted with DCM (3×250 ml). The combined organic fractions were washed with the saturated solution of NH4Cl (2×250 ml) and concentrated to one third of the original volume in vacuo. The resulting solution was washed with water (2×150 ml) and brine (2×150 ml). The combined organic fractions were dried over anhydrous Na2SO4 and evaporated in vacuo. The crude product was purified by column chromatorgraphy (SiO2; EtOAc/MeOH 10:1). Beige solid. Yield 350 mg (47 %). M. p. 259–261 °C. IR (HATR) max = 2926, 1573, 1494, 1290, 822, 622 cm-1. 1H-NMR (500 MHz, CDCl3, 25 °C): δH = 7.01 (d, 6H, 3J = 6 Hz, NPyH), 8.52 (d, 6H, 3J = 6 Hz, NPyH) ppm.

13

C-NMR (125 MHz, d6-DMSO, 25 °C):

δC = 118.6, 151.5, 151.7 ppm. HR-MALDI-MS (DHB): m/z

calculated for

+

C15H12N4 ([M+H] ) 249.11347 found 249.11460.

3.30 Chromophore 154 The title compound was synthesized from 153 (250 mg, 1 mmol) following the general method of N-methylation of pyridine compounds (Chapter 3.6). White solid. Yield 350 mg (>99 %). M. p. 145–146 °C. IR (HATR) max = 3010, 1633, 1511, 1377, 1194, 855 cm-1. 1H-NMR (500 MHz, d6-DMSO, 25 °C): δH = 4.36 (s, 9H, NCH3), 8.06 (d, 6H, 3J = 7.5 Hz, NPyH), 9.09 (d, 6H, 3J = 7.5 Hz, NPyH) ppm.

13

C-NMR (125 MHz, d6-DMSO, 25 °C): δC = 47.1, 122.5, 147.4, 154.6 ppm.

HR-MALDI-MS (DHB): m/z calculated for C18H21N4 ([M-3I])+ 293.17976 found 296.17642.

66

3.31 Chromophore 155 The title compound was synthesized from 6 (150 mg, 0.24 mmol) and pyridin-4-ylboronic acid (174, 122 mg, 1 mmol) following the general method for the Suzuki-Miyaura cross-coupling (Chapter 3.4). Purification of the crude product by column chromatography (SiO2; EtOAc/MeOH 4 : 1) afforded 155. Chicken yellow solid. Yield 104 mg (91 %). M. p. 223–224 °C. Rf 0.35 (SiO2; EtOAc/MeOH 4 : 1). 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 7.26 (d, 6H, 3J = 8.8 Hz, NPhHPy), 7.49 (d, 6H, 3J = 6 Hz, NPhPyH), 7.59 (d, 6H, 3J = 8.8 Hz, NPhHPy), 8.64 (d, 6H, 3J = 6 Hz, NPhPyH) ppm. 13C-NMR (100 MHz, CD2Cl2, 25 °C): δC = 121.2, 124.9, 128.3, 133.1, 147.5, 148.0, 150.5 ppm. HR-MALDI-MS (DHB): m/z calculated for C33H24N4 (M+) 476.1996 found 476.1998.

3.32 Chromophore 156 The title compound was synthesized from 149 (477 mg, 1 mmol) following the general procedure for N-methylation of pyridine compounds (Chapter 3.6). Reddish solid. Yield 900 mg (>99 %). M. p. 156–157 °C. IR (HATR) max = 2848, 2236 (CN), 1592, 1472, 1377, 1169, 831, 728,

718 cm-1.

1

H-NMR

(d6-DMSO,

400

MHz,

25

°C):

H = 4.37 (9H, s, CH3), 7.41 (6H, d, 3J = 8.7 Hz, NPhHPy), 8.20 (6H, d, 3J = 8.7 Hz, NPhHPy), 8.53 (6H, d, 3J = 6.8 Hz, NPhPyH), 9.02 (6H, d, 3J = 6.8 Hz, NPhPyH) ppm. C-NMR (d6-DMSO, 100 MHz, 25 °C): C = 47.0, 123.3, 125.0, 128.8, 129.9, 145.5, 149.0,

13

153.0 ppm. HR-MALDI-MS (DTCB) m/z calculated for C36H33N4+ (M-3I)+ 521.2700 found 521.2701.

3.33 Precursor 157 The title compound was synthesized from 2-bromoxylene (3.7 g, 20 mmol) and KMnO4 (19 g, 120 mmol) following the general method for preparation of carboxylic acids (Chapter 3.7). White solid. Yield (3.5 g, 71 %). M. p. 220–221 °C (lit270 213–214 °C). 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 5.04 (brs, 2H, COOH), 7.56 (t, 1H, 3J = 7.6 Hz, CHAr), 7.74 (d, 2H, 3

J = 7.6 Hz, CHAr) ppm.

13

C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 116.4, 128.1, 131.0,

137.0, 168.1 ppm. 67

3.34 Precursor 158 The title compound was synthesized from 4-bromoxylene (3.7 g, 20 mmol) and KMnO4 (19 g, 120 mmol) following the general method for preparation of carboxylic acids (Chapter 3.7). White solid. Yield (3.2 g, 65 %). M. p. 283–284 °C (lit271 291–292 °C). 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 4.46 (2 H, br s, COOH), 7.86 (1 H, d, 3J = 8.3 Hz, CHAr), 7.95 (1 H, dd, 3J = 8.3 Hz, 4J = 2.0 Hz, CHAr) ppm. 13C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 125.6, 129.8, 131.6, 132.9, 133.2, 134.1, 166.5, 167.1 ppm.

3.35 Precursor 159 The title compound was synthesized from 2-bromomesitylene (4 g, 20 mmol) and KMnO4 (25.3 g, 160 mmol) following the general method for preparation of carboxylic acids (Chapter 3.7). White solid. Yield (3.4 g, 59 %). M. p. 285–286 °C (lit.272 291–294 °C).1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 5.99 (3 H, br s, COOH), 8.19 (2 H, s, CHAr) ppm. 13

C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 121.9, 130.6, 131.3, 137.4, 165.7, 167.4 ppm.

3.36 Precursor 160 The title compound was synthesized from 157 (2.45 g, 10 mmol) following the general procedure for preparation of amides (Chapter 3.8). Yield (1.7 g, 70 %). M. p.. 249–250 °C. 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH

=

7.40–7.42

(2

H,

m,

CHAr),

7.45–7.49

(1

H,

m,

CHAr)

ppm.

13

C-NMR (100 MHz; d6-DMSO):C = 115.3, 127.4, 128.3, 140.5, 169.1 ppm.

HR-MALDI-MS (DHB): m/z calculated for C8H7BrN2O2 ([M+H]+) 242.9764/244.9743 found 242.9767/244.9746.

3.37 Precursor 161 The title compound was synthesized from 158 (2.45 g, 10 mmol) following the general procedure for preparation of amides (Chapter 3.8) Yield (1.85 g, 76 %). M. p. 242–243 °C (lit273 248–249 °C). 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 7.59 (s, 1H, NH2), 7.72 (s, 1H, NH2), 7.78 (d, 1H, 3J = 8.0 Hz, PyH), 7.85 (dd, 1 H, 3J = 8.0 Hz, 4J = 2.0 Hz, CHAr), 7.95 (1 H, d, 4J =2.0 Hz, CHAr), 8.01 (1 H, s, NH2), 8.17 (1 H, s, NH2) ppm.

13

C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 121.9, 127.4,

68

129.5, 132.8, 133.3, 139.2, 166.4, 168.7 ppm. HR-MALDI-MS (DHB): m/z calculated for C8H7BrN2O2 ([M+H]+) 242.9764/ 244.9743 found 242.9760/244.9747.

3.38 Precursor 162 The title compound was synthesized from 159 (2.89 g, 10 mmol) the general procedure for preparation of amides (Chapter 3.8). Yield (1.35 g, 56 %). M. p. 290–292 °C. 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 7.64 (1 H, s, NH2), 7.77 (2 H, s, NH2), 7.99 (2 H, s, NH2), 8.06 (2 H, s, CHAr), 8.22 (1 H, s, NH2) ppm. 13C-NMR (100 MHz, d6-DMSO, 25 °C): δC =127.5, 129.05, 132.32, 138.1, 165.8, 167.7 ppm. HR-MALDI-MS (DHB): m/z calculated for C9H8ClN3O3 (M+) 241.0249 found 241.0249.

3.39 Precursor 163 The title compound was synthesized from 160 (730 mg, 3 mmol) following the general procedure for preparation of nitriles (Chapter 3.9). Yield (590 mg, 95 %). M. p.. 191–192 °C (lit.273 190–190.5 °C). 1H-NMR (400 MHz, CDCl3, 25 °C): δH = 7.59 (1 H, t, 3J = 7.8 Hz, CHAr), 7.87 (2 H, d, 3J = 7.8 Hz, CHAr) ppm. 13C-NMR (100 MHz; CDCl3): C = 115.8, 118.3, 128.6, 128.9, 137.8 ppm. EI-MS (70 eV) m/z (rel. int.): 206/208 (M+, 100 %), 127 (40), 100 (30), 75 (20).

3.40 Precursor 164 The title compound was synthesized from 161 (730 mg, 3 mmol) following the general procedure for preparation of nitriles (Chapter 3.9). Yield (602 mg, 97 %). M. p. 191–193 °C (lit.273193–193.5 °C). 1H-NMR (400 MHz, CDCl3, 25 °C): δH = 7.70 (1 H, dd, 3J 8.4, 4J 2.0, CHAr), 7.86 (1 H, d, 3J 8.4, CHAr), 7.93 (1 H, d, 4J 2.0, CHAr) ppm. 13C-NMR (100 MHz; CDCl3): C = 112.9, 115.5, 116.3, 118.0, 131.1, 134.8, 136.7, 137.5 ppm. EI-MS (70 eV) m/z (rel. int.): 206/208 (M+, 100 %), 127 (45), 100 (35), 75 (25).

69

3.41 Precursor 165 The title compound was synthesized from 162 (730 mg, 3 mmol) following the general procedure for preparation of nitriles (Chapter 3.9). Yield (482 mg, 86 %). M. p. 167-168 °C (lit261 167–168 °C). 1H-NMR (400 MHz, CDCl3, 25 °C): δH = 8.17 (2 H, s, CHAr) ppm.

13

C-NMR (100 MHz, CDCl3, 25 °C):

δC =112.7, 113.5, 114.3, 117.3, 140.2, 144.4 ppm. EI-MS (70 eV) m/z (rel. int.): 187 (M+, 100 %), 152 (10), 125 (14), 100 (12), 75 (18).

3.42 Precursor 166 Title compound was prepared from 6 (164 mg, 0.26 mmol) and propargyl alcohol (250 l, 4.6 mmol) following the general procedure for the Sonogashira cross-coupling (Chapter 3.3). Subsequent column chromatography (SiO2; EtOAc/hexane 1 : 1) afforded the desired product as a reddish solid. Yield 98 mg (91%). Rf 0.45 (SiO2; EtOAc/hexane 1 : 1). M.p. 166–167 C; IR (neat): max = 3269, 2237, 1595, 1496, 1316, 1288, 1268, 1011, 950, 832, 678 cm-1. 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 4.28 (6 H, d, 3J = 6.0 Hz, CH2), 5.30 (3 H, t, 3J = 6.0 Hz, -OH), 6.98 (6 H, d, 3J = 9.0 Hz, CHAr), 7.36 (6 H, d, 3J = 9.0 Hz, CHAr) ppm.

13

C-NMR (100 MHz, d6-DMSO, 25 °C): δC = 49.5, 83.3, 89.5, 117.3, 123.9,

132.8, 146.2 ppm. HR-MALDI-MS (DHB): m/z calculated for C27H21NO3 (M+) 407.15160 found 407.15090.

3.43 Precursor 167 Title compound was prepared from 6 (150 mg, 0.24 mmol) and 3,3-diethoxypropyne (500 mg, 3.9 mmol) following the general procedure for the Sonogoashira cross-coupling (Chapter 3.3). Subsequent column chromatography (SiO2; EtOAC/hexane 1 : 1) afforded 167. Reddish

oil.

Yield

135

mg

(90

%).

Rf 0.65

(SiO2;

EtOAc/Hexane 1:1). 1H-NMR (400 MHz, d6-DMSO, 25 °C): δH = 1.26 (18 H, t, 3J = 7.2 Hz, CH2CH3), 3.61–3.82 (12 H, m, CH2CH3), 5.48 (3 H, s, CH(OEt)2), 7.05 (6 H, d, 3J = 8.8 Hz, CHAr), 7.43 (6 H, d, 3J = 8.8 Hz, CHAr) ppm.

13

C-NMR (100 MHz, d6-DMSO, 25 °C):

δC = 15.4, 61.2, 84.6, 85.4, 92.0, 119.0, 120.8, 125.7, 146.0 ppm. HR-MALDI-MS (DHB): m/z calculated for C39H45NO6 (M+) 623.3241 found 623.3241. 70

3.44 Precursor 168 Title compound was prepared following two procedures A and B listed bellow from 166 and 167, respectively. Procedure A: To a suspension of triole 166 (100 mg, 0.25 mmol) in DCM (40 mL) Dess-Martin periodinane (3.0 g, 1.06 mmol) was added and the reaction mixture was stirred 3 hours at 20 C, poured on saturated aqueous solution of NaHCO3 (30 mL) and extracted with DCM (250 ml). The combined organic extracts were washed with water (250 ml), dried (Na2SO4) and concentrated in vacuo. The crude product was purified by column chromatography (SiO2; EtOAC/hexane 1 : 2) to afford 168 as red solid. Procedure B: Compound 167 (50 mg, 0.08 mmol) was dissolved in 3 ml of DCM. Formic acid (20 mg, 0.44 mmol) was added dropwise and the solution was stirred for 1 h at 20 °C. The reaction mixture was subsequently filtered through the short plug (SiO2; DCM). Combined organic fractions were dried over anhydrous Na2SO4 and concentrated in vacuo to afford 168 as a reddish solid. Yield of Procedure A: 135 mg (90 %); yield of Procedure B: 20 mg (61 %). Rf 0.65 (SiO2; EtOAc/Hexane 1:1) 1H-NMR (400 MHz, CDCl3, 25 °C): δH = 1.26 (18 H, t, 3J 7.2, CH2CH3), 3.61 – 3.82 (12 H, m, CH2CH3), 5.48 (3 H, s, CH(OEt)2), 7.05 (6 H, d, 3J 8.8, CHAr), 7.43

(6 H,

d,

3

J

8.8,

CHAr)

ppm.

13

C-NMR

(100

MHz,

CDCl3,

25 °C):

δC = 15.4, 61.2, 84.6, 85.4, 92.0, 119.0, 120.8, 125.7, 146.0 ppm. HR-MALDI-MS (DHB): m/z calculated for C39H45NO6 (M+) 623.3241 found 623.3241.

71

4 Results and discussion 4.1

Design of target D--A chromophores

Chromophores 137, 138, 140, 142 and 155 shown in the experimental part are identical with the compounds 78, 42, 63, 87 and 76 discussed in the theoretical part. They were re-numbered for better clarity and in order to properly fit the charts of compounds listed below.

Figure 38. Chart of target TPA-based chromophores 137–148.

Two classes of D--A molecules were developed within the scope of this dissertation work. Both series are based on tripodal arrangement. The first family of derivatives comprises TPA-based molecules 137–148 (Figure 38) bearing various peripheral cyano-acceptors. According to the curent state-of-the-art (Chapter 2.2.2), this series of tripodal push-pull molecules was designed as 2PA absorbers. The main idea was to perform structural variations of the peripheral acceptors and tuning of the -linker in order to evaluate thorough structureproperty relationships. This would provide deeper insight into chromophore structure related to its 2PA activity and, subsequently, would also allow structural optimization directed 72

towards efficient 2PA absorbers. An effect of the spatial arrangement (branching) of chromophores can further be studied by comapring linear (140l, 141l), quadrupolar (140q, 141q) and tripodal molecules (140, 141) prepared within this series. The second family of derivatives consists of model aminopyridines 149, 151, 153 and 155 with different spatial arrangement (Figure 39). Pyridine was designed not only as a peripheral acceptor moiety but also as an anchoring group capable of protonation. These structural features predestinate the aforementioned aminopyridines to be used as guest molecules for intercalation into acid layered inorganic hosts. N-Quaternized analogues 150, 152, 154 and 156 mimic the species gained upon the intercalation process.

Figure 39. Chart of target aminopyridine based chromophores 149–156.

4.2

Synthesis

In general, the synthesis of chromophores 137–148 and 155 including 140q, 140l, 141q and 141l involves three reaction steps: synthesis of the properly substituted TPA derivative (D-building block), preparation of the acceptor moieties (A-building blocks) and their final combination.

73

Figure 40. Chart of used A-building blocks.

For the synthesis of 138, 139, 140(ql), 142, 147 and 155, commercial A-building blocks 169–174 were employed (Figure 40). These inlcude acrylonitrile (169), boronic acids (170, 174), terminal acetylene (171), malononitrile (172) and 5-bromothiophen-2-carbonitrile (173). The synthesis of target chromophores 141(ql), 144 and 148 required A-building blocks 175–177 (Figure 40) that were synthesized by the known methods published in the literature.5,274,275

Scheme 19. Newly developed synthetic pathway to precursors 163–165.

A straightforward synthetic pathway towards di- and tricyano substituted halogenbenzenes 163–165 was developed during my doctoral work (Scheme 19). The synthesis has been accomplished in a modular manner starting from di- and 74

trimethylbromobenzenes, which were oxidized to corresponding acids 157–159 using KMnO4 in tBuOH. The carboxylic acids, after SOCl2-based activation, were treated with gaseous NH3 to afford amides 160–162. The conversion of 159 to 162 was accompanied by a halogen replacement and, therefore, precursor 162 is not expected bromotriamide but rather chlorotriamide. Final dehydratation into nitriles 163–165 was carried out by trifluoroacetic anhydride (TFAA) in dioxane/pyridine. Three

parent

D-building

blocks

based

on

triphenylamine,

namely tris(4-

iodophenyl)amine (6),22 tris(4-ethynylphenyl)amine (8)48 and tricarbaldehyde (10)54 were synthesized following the known procedures. Trialdehyde 168 with the -system extended by acetylenic unit was newly prepared by a threefold Sonogashira cross-coupling between easily accessible 6 and either propargyl alcohol (yielding 166) or 3,3-diethoxyprop-1-yne to afford 167. Trialcohol 166 was oxidazed to 168 with Dess-Martin reagent, acetal 167 was hydrolyzed to 168 by formic acid (Scheme 20). Whereas both initial Sonogashira crosscouplings provided intermediates 166 and 167 in similar yields, the Dess-Martin oxidation of 166 proved to be more efficient than the acetal group removal on 167 (Scheme 20). Hence, the synthetic pathway via 166 proved to be more useful strategy towards trialdehyde 168.

Scheme 20. Two synthetic pathways leading to trialdehyde 168.

Starting from tricarbaldehyde 10, the CN groups in 137 were established via threefod Beckmann-type oxime formation and its subsequent dehydratation (Scheme 21). This represents new synthetic access to 137, which until now was prepared exclusively via coppercatalyzed cyanation on 6.150,263,276 However, cyanation generally afforded 137 in lower yield than the aforementioned procedure.

75

Scheme 21. Alternative synthesis to chromophore 137.

The final step of the synthesis leading to 138–148 mostly involved a threefold crosscoupling reaction or Knoevenagel condensation (Scheme 22). Three types of Pd-catalyzed cross-couplings were used: Suzuki-Miyaura, Sonogashira and Heck-Mizoroki reactions.

Scheme 22. Combination of D- and A-parts leading to target compounds.

76

Chromophore 138 was prepared via Heck-Mizoroki reaction described in the literature with comparable yield.150 Threefold Suzuki-Miaura cross-coupling reactions between 6 and boronic acids 170 and 174 were carried out under standard conditions (Chapter 3.3.4) delivering chromophores 139 and 155 in satisfactory yields of 76 and 91 %, respectively. The Sonogashira cross-coupling between 6 and terminal acetylene 175 provided lower yield of 140 than that reported by Ogilby et al. (69 vs. 94 %).265 On the other hand, threefold Suzuki-Miyaura cross-coupling between 6 and 171 afforded chromophore 141 in a slightly improved yield of 76 % compared to the Horner–Wadsworth–Emmons reaction carried out by Cho et al.125 Target chromophore 144 bearing peripheral dicyanoimidazole (DCI) acceptor moieties was prepared by Heck–Mizoroki olefination of 6 and vinazene 176 in satisfactory yield of 74 %. The aforementioned Sonogashira protocol (Pd(II) precatalyst, CuI, TEA, THF, 70 °C) proved to be unefficient for cross-coupling of triacetylene 8 and halogenated dinitriles 163–165. Hence, optimized conditions (Pd(0) precatalyst, CuI, TEA, 1,4-dioxane, 92 °C) were employed affording chromophores 145 and 146 in modest yields. The attained yields were apparently affected by predominant formation of one- and twofold cross-coupling products, which proved tedious to separate and to suppress even an excess of 163 or 164 were used. Furthermore, a similar Sonogashira reaction with trinitrile 165 proved to be unsuccessful at all, which is most likely caused by the presence of chloro instead of bromo substituent (see above). A similar cross-coupling reactions with thiophene analogues 173 and 177 afforded chromophores 147 and 148 in low yields of 25 and 16 %, respectively. An opposite Sonoghashira cross-coupling of 6 and terminal acetylenes, generated from 163–165 via reaction with TMSA, has also been attempted. However, such terminal acetylenes proved to be instable and cannot be prepared in reasonable yields. Dicyanovinyl moieties in 142 and 143 were introduced via threefold Al2O3-catalyzed Knoevenagel reactions of aldehydes 10 and 168 and malononitrile. Whereas extended aldehyde 168 underwent this reaction smoothly, tricarbaldehyde 10 reacted only partially. Alumina had to be used exclusively in Brockmann activity II-III, reaction was observed to be sensitive to the quality of the solvent, while a presence of drying reagent such as Na2SO4 did not affect the attained yields.

77

Scheme 23. Synthetic route to iodinated TPA derivatives and linear and quadrupolar chromophores.

Scheme 23 shows the synthetic route to mono-, di- and triiodinated triphenyl amine precursors 178, 179 and 6. The well-established threefold iodination of TPA using the HgO/I2 system afforded tris(4-iodophenyl)amine 6 in 88% yield.184 However, the iodination using HgO as a Lewis acid lacks selectivity towards mono- and bisiodinated products 178 and 179. Hence, the iodination was carried out using AgNO3/I2/EtOH system, similar to a solvent free protocol used for iodination of carbazole.277 These were further used to access linear chromophores 140l and 141l as well as quadrupolar compounds 140q and 141q. Going through the whole series including also tripodal molecules 140 and 141 (Scheme 22), the attained yields steadily decrease with increasing the multiplicity of the cross-coupling. Aminopyridine chromophores were prepared either via C-C or C-N cross-coupling reaction. Whereas 155 can easily be synthesized from 6 and pyridin-4-ylboronic acid 174 via standard Suzuki-Miyaura reaction (see above, Scheme 22), chromophore 151 was prepared by the known reaction of pyridine, PCl3 and 149 in 44% yield (Scheme 24).268 Considering wellknown and widely utilized 2-pyridyl analogue,85,278,279 it is quite surprising that 153 has been envisaged hypothetically as lately as in 2010 (Ref.280) with no evidence of its successful 78

synthesis until this work. With dipyridylamine 151 in hand, introduction of the third pyridine branch was initially attempted via Buchwald-Hartwig reaction with 4-iodopyridine yielding no desired product. However, by adopting copper(I)-catalyzed strategy of Sarges et al.269 and upon optimization of the reaction condition, 153 was prepared in 47% isolated yield. N-Methylated pyridinium derivatives 150, 152, 154 and 156 were prepared by simple quaternization using excess of CH3I. This reaction provided pyridinium iodides 150, 152, 154 and 156 in almost quantitative yields for all substrates.

Scheme 24 Synthetic route towards aminopyridines 151 and 153 and their quaternization.

4.3 4.3.1

Physical properties of two-photon absorbers 137–148 Thermal properties

Thermal behaviour of compounds 137–148 was studied by differential scanning calorimetry (DSC). Representative thermograms (chromophores 138 and 145) are shown at Figure 41 while Table 10 lists the measured melting temperatures (Tm) and temperatures of thermal decompositions (Td). The measured melting points of 137–148 range from 84 to 343 °C. The temperature of decomposition was estimated within the range of 176–477 °C. Compound 137 provided very sharp peak of melting/crystallization at 343/263 °C and do not undergo decomposition until its boiling point (436 °C). Thermal behaviour of compounds 138, 139, 141–145 and 147–148 is very similar with the melting point peak followed by subsequent decomposition. Thermograme of compound 140 contains a wide peak of endotermic process explainable as enantiotropic solid-solid transition (37–82 °C), melting point at 217 °C and, surprisingly, no decomposition peak. However, the sample was clearly 79

carbonized after heated up to 500 °C. For compound 146, thermal decomposition preceded the melting point. An overview on the series of molecules 137–148 (Table 10) reveals significantly low thermal stability (melting point, Td) of DCV-terminated tripodal compounds 142 and 143. On the other hand, TPA derivatives substituted with cyanoaromates 139–141 and 145–146 resisted thermal decomposition above 300 °C. Heterocyclic acceptor moieties such as DCI and (di)cyanothiophene as in 144 and 147–148 bring also noticeable thermal stability up to 366 °C, especially for the imidazole-terminated compound 144. The measured DSC data of compounds 137–148 reflects their different molecular structure (varied peripheral acceptors and -linker).

Figure 41. Representative thermograms of compounds 138 and 145.

The melting points within the most evaluated subseries of compounds 137–141 are mostly affected by an insertion of multiple bonds. In general, chromophores bearing triple bond proved less stable than the corresponding olefinic derivatives. This can be further demonstrated by the DCV acceptor linked to the TPA core via acetylenic spacer in 143, which lowered the thermal stability very significantly when compared to 142 (Tm = 61 °C, Td = 146 °C). Chromophores bearing benzene-derived acceptors (e.g. 140 or 145, 146) are generally more thermally stable than the corresponding thiophene derivatives (e.g. 147 and 148). Chromophore 144 with the imidazole-based acceptor (DCI) showed the highest thermal resistance among all heterocyclic compounds (144, 147–148) with Td = 366 °C.

80

Table 10. Thermal and electrochemical properties of chromophores 137–148. Comp.

Tm

Td a

E1/2(ox1) b

c

E1/2(red1) c

E c

EHOMO d

ELUMO d

[°C]

[°C]

[V]

[V]

[V]

[eV]

[eV]

137

343

-

1.49

–2.01

3.50

–5.92

–2.42

138

275

317

1.12

–1.74

2.86

–5.55

–2.69

139

329

340

1.02

–2.02

3.04

–5.45

–2.41

140

217

-

1.04

–1.85

2.89

–5.47

–2.58

141

291

477

0.85

–1.80

2.65

–5.28

–2.63

1.41

-

d

-

–5.84

-

d

-

–5.72

-

142

145

322

143

84

176

1.29

-

144

188

366

0.97

–1.66

2.63

–5.40

–2.77

145

327

333

1.16

–1.55

2.71

–5.59

–2.88

146

-

282

1.15

–1.44

2.59

–5.58

–2.99

147

191

240

1.09

–1.45

2.54

–5.52

–2.98

148

198

252

1.17

–1.41

2.58

–5.60

–3.02

140l

101

303

0.98

-1.88

2.86

-5.41

-2.55

140q

232

235

1.01

-1.88

2.89

-5.44

-2.55

141l

131

-

0.84

-1.85

2.69

-5.27

-2.58

141q

203

-

0.84

-1.86

2.70

-5.27

-2.57

a

Tm = melting point (the point of intersection of a baseline before the thermal effect with a tangent). bTd = thermal decomposition (pyrolysis in N2 atmosphere). c E1/2(ox1) and E1/2(red1) are half-wave potentials of the first oxidation and reduction, respectively; all potentials are given vs. SCE; E = E1/2(ox1) - E1/2(red1). d – EHOMO/LUMO = E1/2(ox1/red1) + 4.429 (Ref.291).

Clear trends are observable from the perspective of branching of chromophores 140/l/q and 141/l/q (Table 10). As can be seen, the melting points increased with the increasing number of branches (with the exception of 140). On the other hand, the decomposition temperatures (Td) seem to be not influenced by the linear, quadrupolar or tripodal arrangement. 4.3.2

Electrochemistry Electrochemical measurements of chromophores 137–148 were carried out in

acetonitrile containing 0.1 M Bu4NPF6 in a three electrode cell by cyclic voltammetry (CV), rotating disk voltammetry (RDV) and polarography. The working electrode was platinum disk (2 mm in diameter) for CV and RDV experiments. A saturated calomel electrode (SCE) separated by a bridge filled with a supporting electrolyte and a Pt wire were used as reference and auxiliary electrodes. The acquired data are summarized in Table 10.

81

The measured half-wave potentials of the first oxidation and reduction (E1/2(ox1) and E1/2(red1)) of chromophores 137–148 were found within the range of 0.85 to 1.49 and –1.41 to –2.02 V, respectively. The first reduction and oxidation are one-electron processes, followed by subsequent oxidations and reductions, and are obviously a function of the peripheral acceptor and the -linker (Table 10). Whereas the first oxidation can be attributed to the central TPA donor, the first reduction is mostly localized on the peripheral CN groups and the adjacent -system. The first oxidation potentials of chromophores 137–141 bearing monocyano-substituted acceptor moieties steadily decreased from 1.49 to 0.85 V as a function of the -system elongation. The first reduction potentials showed similar trends with exception for 139 in which nonplanar biphenyl -linker allows only reduced ICT. The difference between the first oxidation and reduction potentials (electrochemical gap, E) represents a straightforward way for the evaluation of the ICT. When going from 137 (E = 3.50 V) to 138 (E = 2.86 V), the electrochemical gap decreased by 0.64 V, as a consequence of the insertion of an additional olefinic subunit. However, further -system extension as in 139 resulted in an increased gap of 3.04 V. This demonstrates “ICT transparency” of the olefinic unit in comparison to aromatic 1,4-phenyle moiety.281,282 Further extension and planarization of the -linker by acetylenic and olefinic subunits (139 vs. 140 and 141) lowered the electrochemical gap to 2.65 V. Dicyano-substituted (hetero)aromatic moieties attached to TPA core affected both the first oxidation and the reduction potentials (144–148, Table 10). The evaluation of the ICT based on the overall electrochemical gap E implies that these (hetero)aromates impart stronger resonance effect than aromates (E of 2.71–2.54 vs. 3.50–2.65 V for 137–141 vs. 144–148). Positioning of the CN groups along the (hetero)aromatic scaffold plays also significant role as can be seen for instance on chromophores 145 and 146. The latter, 2,4-dicyano-substituted chromophore showed a reduced gap by 0.12 V. The lowest electrochemical gap (E = 2.58 V) was measured for chromophore 147 bearing cyano-acceptor based on polarizable thiophene with the cyano group attached at the resonant and most extended C5 position (as compared to dicyano acceptor in 148). A comparison of chromophores 140 and 147 also allows comparison of 1,4-phenylene and 2,5-thienylene -systems.34 With very similar oxidation potentials (1.04 and 1.09 V), the later showed significantly lowered first reduction potential (-1.45 vs. -1.85 V) as well as the electrochemical gap (E = 2.89 vs. 2.54 V).

82

Whereas character of the acceptor and -system length/composition affected the electrochemical behavior of tripodal molecules 137–148 significantly, the number of branches appears to have limited or almost no influence on the electrochemical parameters (Table 10). When going from 140l via 140q to 140, the first oxidation potential is slightly shifted to more positive values with overall E1/2(ox1) = 0.06 V. Considering the central amino donor as a main oxidation centre, this observation reflects its lowered electron density caused by attaching more electron acceptors (enhanced/spread ICT). All chromophores 141, 141q and 141l showed alsmos identical electrochemical data. 4.3.3

One photon absorption and emission Target chromophores are coloured molecules, their colours range from yellowish to

red (Figure 42), and showed also strong fluorescent properties with color of the emission rangin from blue to red (Figure 43).

Figure 42. Colors of chromophores 137–148 (from left to right, DCM).

Figure 43. Colors of chromophores 137–148 (from left to right, DCM) under irradiation with handheld UVlamp (365 nm).

Optical properties of 137–148 were investigated by electronic absorption and emission spectra; the longest-wavelength absorption/emission maxima maxA/maxF, the fluorescence quantum yields F and the Stokes shifts are summarized in Table 11. Figure 44 shows absorption and emission spectra of representative chromophores 141, 143–145 and 147.

83

Figure 44. Normalized absorption and emission spectra of compounds 141, 143–145, 147.

Whereas the absorption maxima range from 339 to 453 nm, the emission maxima are red-shifted to 377–611 nm. The absorption spectra are dominated by one intense CT-band whose position is clearly dependent on the nature of the appended cyano-acceptors and the -system. When considering the monocyano-substituted series of molecules 137–141, the

maxA values showed a very similar trend as seen for the electrochemical gaps E. Namely, extension of the -system by olefinic (137 vs. 138) or aromatic units (139 vs. 138), planarization (140 and 141 vs. 139) and further elongation by acetylenic subunit (140) affected the absorption maxima within the range of 339 to 403 nm. It should be noted that the longest-wavelength absorption maxima of 139–148 correlate very tightly with the measured electrochemical gap E (Figure 45).

84

1240/maxA = (1.25±0.24) + (6.79±0.86) 10 -1 E n = 10, s = 7.62 10-2, r = 0.941

Figure 45. Correlation of the energy of the longest-wavelength absorption maxima and the electrochemical gap. Table 11. The survey of (non)linear optical properties of compounds 137 to 148. Comp.

maxA

maxF a

 a

F

Stokes shift 1

 (exc [nm]) b

[nm/eV]

[nm/eV]

[%]

[cm– ]

[GM]

137

339/3.66

377/3.29

0.62

2970

-

138

394/3.15

460/2.70

0.48

3640

260 (770)

139

372/3.33

448/2.77

0.64

4560

566 (760)

140

387/3.20

458/2.71

0.59

4010

785 (780)

141

403/3.08

510/2.43

0.51

5210

1100 (810)

142

453/2.74

549/2.26

0.29

3860

757 (830)

143

470/2.64

611/2.03

0.29

4910

667 (810)

144

413/3.00

497/2.49

0.59

4090

620 (810)

145

420/2.95

533/2.33

0.69

5050

852 (810)

146

414/3.00

499/2.48

0.55

4126

631 (810)

147

397/3.12

475/2.61

0.46

4140

148 (750)

148

412/3.01

516/2.40

0.49

4890

375 (830)

Measured in THF; b The wavelength of the maximum (2) cross-section is shown in parenthesis (measured in THF).

a

Chromophores 142 and 143 bearing strong electron DCV acceptors showed the most bathochromically shifted CT-bands with maxA at 453 and 470 nm, respectively. In contrast to 137–141, chromophores 144–146 and 148 exhibited red-shifted absorption maxima up to 412–420 nm as a result of the appended dicyano-substituted (hetero)aromatic acceptor moieties. However, the differences in maxA are just within the range of 8 nm, which implies 85

that, in contrast to electrochemical gap, the central (hetero)aromatic -system and positioning of the CN groups do not affect the absorption properties very significantly. The fluorescence spectra exhibited one single band with the maxF appearing at 377–611 nm. In general, its position is affected by the same structural features as the aforementioned absorption bands. Both positions of the longest-wavelength absorption and fluorescence maxima showed tight correlations (Figure 46). The quantum yields lie within the range of 0.29 to 0.69. The lowest quantum yields were measured for chromophores 142 and 143 with strongly electron withdrawing DCV moieties. The weaker (di)cyano acceptors in 137–141 and 144–148 lead generally to blue-shifted emission with high quantum yield. This is in accordance with our previous observations on linear and X-shaped push-pull molecules feat. strong/weak ICT.281

1240/maxF = -(1.05±0.25) + (1.17±0.08) 1240/maxA n = 12, s = 7.16 10-2, r = 0.976

Figure 46. Correlation of the energies of the longest-wavelength fluorescent and absorption maxima.

The branching effect in the series of compounds 140/140q/140l and 141/141q/141l were also investigated. Figure 47 shows the absorption and fluorescence spectra in THF; the principal photophysical parameters are given in Table 12. When going from linear (l) to quadrupolar (q) chromophores, the absorption spectra are red-shifted as a result of attaching more electron acceptors/branches and indicate an electronic coupling between the branches. In the absorption spectra of the quadrupolar compounds 140q and 141q, a shoulder located at the high-energy side of the peak, close to the position of the maxima of linear chromophores 140l and 141l, can be observed. This split of the absorption bands results from the strong coupling between branches in the case of 140q and 141q. This splitting is predicted by the 86

Frenkel exciton model, which is also applied to H- and J-aggregates and assumes electrostatic interaction of the chromophores.

Normalized Intensity

1,0 140l 140q 140

0,8 0,6

(a)

0,4 0,2 0,0 350

400

450

500

550

600

650

Normalized Intensity

1,0 141l 141q 141

0,8 0,6 (b) 0,4 0,2 0,0 350

400

450

500

550

600

650

Wavelength (nm)

Figure 47. The influence of number of branches on the absorption and emission spectra. Table 12. Effect of branching on (non)linear optical properties of 140(ql) and 141(ql).

Comp.



A max -1 a



 -1 a

F max -1 a



F

(nm eV )

(M cm )

(nm eV )

(%)

140l

378/3.28

13120

472/2.63

140q

390/3.18

57621

140

387/3.20

141l

a

Stokes

2)

shift

(exc [nm])

-1

b

(cm )

(GM)

0.80

5270

641 (750)

461/2.69

0.73

3950

1025 (750)

80141

458/2.71

0.59

4100

1195 (760)

392/3.16

20299

495/2.51

0.63

5310

284 (750)

141q

414/3.00

31033

504/2.46

0.61

4310

1050 (750)

141

403/3.08

53613

510/2.43

0.51

4970

1100 (810)

Measured in THF. b The wavelength of the maximum  cross-section is shown in parenthesis (measured in THF). a

This model predicts that in the quadrupolar V-shaped molecules, the singlet excited state of the linear compounds splits into two bands which both are one photon allowed while the lower energy band has stronger oscillator strength. On the other hand, the excited state of tripodal compounds with C3 symmetry is split into three states. The two states are degenerate and lay at the low-energy side of the linear chromophore while the third state is located at the higher-energy and is predicted to have zero oscillator strength which well predicts a single, no shouldered or broadened peaks of all tripodal compounds 137–148. As expected, the molar extinction coefficient of the chromophores increases upon branching. In series 140(ql), though, the increase is not linear to the number of branches indicating a strong branch 87

coupling. In series 141(ql), the value of extinction coefficient is approximately proportional to the number of branches indicating a nearly independent bahavior of branches. Regarding the fluorescence spectra, 140 and 140q exhibit a hypsochromically shifted spectrum compared to that of 140l. In series 141(ql), on the other hand, a red-shifted fluorescence is observed for 141q and 141 vs. 141l. In both cases, the observed differences in the fluorescence spectra indicate a coupling between branches. The fluorescence quantum yields decrease upon branching, implying increased non-radiative pathways but they are maintained to relatively high values (Table 12). 4.3.4

Two photon absorption (2PA) The 2PA properties of tripodal chromophores 137–148 were studied by means of two-

photon excited fluorescence spectroscopy within the spectral range from 750 to 850 nm. The advantage of this method is that low concentrations are used and that the order of the nonlinear effect is monitored by detecting the intensity of the emitted fluorescence as a function of excitation power. In the case of two-photon excitation, the emitted fluorescence is dependent on the square of the excitation laser power. This was checked in all experiments to confirm the 2PA process. The excitation power was in all cases kept below 20 mW in order to minimize thermal effects and in most cases the 2PA cross-sections were measured within the range of 10–20 mW. The samples were 10-4 M solutions of the dyes in THF. The contribution of the solvent was taken into account by subtracting the intensity of scattered light, obtained by a cuvette containing the solvent only, from the measurements. The two-photon absorption cross-sections were determined by using Rhodamine B in methanol (10-4 M concentration), as reference. The 2PA spectra of all compounds, i.e the 2PA cross-sections (2)) as a function of excitation wavelength, are shown in Figure 47. For a better comparison of the 2PA properties, target chromophores 137–148 were split in four groups according to the peripheral acceptor moieties. Whereas the first group includes chromophores 138–141 with monocyano acceptors, chromophores 142 and 143 in the second group possess DCV acceptors. Third and fourth group of molecules consist of dicyano aromatic (145 and 146) and (di)cyano heteroaromatic acceptor moieties (144, 147–148), respectively. In all cases, good 2PA properties were observed with the 2PA cross-section exceeding 1000 GM for compound 141. In general, chromophores 140 and 141 with monocyano acceptors displayed larger 2PA cross-section than the other tripodal molecules in the whole series. Moreover, these two chromophores also exhibited good fluorescence quantum yields (>0.50). The 2PA results are summarized in Table 11. 88

2PA cross section  (GM)

1200 1000

138 141

139 147

800

140

142 143

700

(a)

(b)



600 800

500

600

400 300

400

200 200 0 740

100 760

780

800

820

840

860

0 740

760

780

800

820

840

860

Wavelength (nm)

2PA cross section 



(GM)

700 800

(c)

600 500

600

144 147 148

(d)

400 400

300

145 146

200

200 100

0 740

760

780

800

820

840

860

0 740

760

780

800

820

840

860

Wavelength (nm)

Figure 48. 2PA properties of chomophores 138–148.

Compound 137 showed negligible 2PA cross-sections within the investigated spectral area. It was observed that by increasing the length of the -linker, i.e passing from 137 to 140 and 141, the 2PA cross-sections increased. In addition, it is also obvious that upon changing the acetylenic π-conjugated bridge by an olefinic one (140 vs. 141), the 2PA cross- sections significantly increased up to 1100 GM (at 810 nm) for 141 while this is 785 GM (at 780 nm) for 140. Since the fluorescence quantum yields of 140 and 141 are similar (Table 11), the 2PA action cross-section product Φ×(2) is again higher for 141 than for 140. This renders molecule 141 as a promising candidate for up-converted lasing or two-photon imaging. A replacement of the 1,4-phenylene moiety in 140 with 2,5-thienylene one (147), led to more than seven-times decrease of the 2PA cross-sections (Table 11, 1100 vs. 148 GM). Hence, heteroaromatic polarizable moiety based on thiophene in 147 did not bring expected higher 2PA activity. Another conclusion drawn from Figure 48a is that the peaks of the 2PA spectra appear at approximately twice the wavelengths of the one photon absorption spectra. This is in accordance with the two-photon allowed states for octupolar molecules. Specifically, the 2PA spectrum of 140 is blue-shifted compared to 141 while that of 139 is blue shifted compared to 138 as in the case of their one-photon absorption spectra. 89

The 2PA spectra of chromophores 142 and 143 bearing the strongest DCV acceptor are shown in Figure 48b. Chromophore 142 exhibited a large 2PA cross-section of 760 GM at 830 nm. Interestingly, an extension of the π-conjugated path by an additional acetylene subunit as in 143 did not lead to enhanced 2PA cross-sections. The fluorescence quantum yields of 142 and 143 are relatively low making the Φ×(2) values significantly smaller than those of compounds 140 and 141. However, it should be noted that, according to their onephoton absorption spectra, the maximum of the 2PA spectra of 142 and 143 is expected at wavelengths close to 900 nm, which is not covered by our experiment. On the other hand, chromophore 142 with DCV acceptor exhibited much larger 2PA cross-section than structurally related 138, which possesses only one cyano group. Figure 48c presents the 2PA cross-sections of 145 and 146 bearing dicyano aromatic acceptors with different orientation of the appended CN groups. The position of the cyano groups played significant role as 145 exhibited an approximately 1.35-times larger 2PA crosssections compared to 146. Moreover, the fluorescence quantum yield is higher for 145 (0.69) compared to 146 (0.55), which provides 145 a larger Φ×2) value. A comparison of the structurally related chromophores 146 and 140, with di- and monocyano aromatic acceptor moieties, reveals that the second cyano group has broadened and red-shifted the 2PA spectra. This is in accordance with one photon absorption spectra, but, on the other hand, it also causes a decrease of the 2PA response. Finally, the 2PA cross-sections of chromophores 144, 147 and 148 with (di)cyanoheteroaromatic acceptors are compared in Figure 48d. Chromophores 147 and 148 with thiophene acceptors exhibited relatively small 2PA cross-section values compared to their analogues 140 and 146 having a phenyl ring. Thus, a replacement of 1,4-phenylene by 2,5-thienylene moieties coupled either to cyano or dicyano groups, is a not useful strategy towards increasing the 2PA activity in TPA-derived tripodal chromophores. This is in contrast to general trends observed for second order NLO chromophores.283 However, an addition of the second cyano group into 147 leads to 148 with more than three-times higher 2PA cross-section without affecting the florescence quantum yield. This makes the thiophene substituted chromophores 147 and 148 extremely sensitive to the number of cyano groups. On the other hand, 2PA cross-sections measured for the analogous chromophores 140 and 146 with 1,4-phenylene parent moieties showed less sensitivity. Chromophore 144 bearing three peripheral DCI acceptor units exhibited a relative large 2PA cross-section of 620 GM at 810 nm accompanied by a good quantum yield of 0.59. Although, a straightforward comparison of the 2PA properties of the herein studied compounds with literature data is not easy because of 90

various experimental approaches used (sample concentration, solvent used, pulse duration, laser power, spectral range etc., see chapter 2.2.2), chromophores 140 and 141 are found to exhibit similar or better 2PA activity compared with other tri-branched compounds with D(-π-A)3 arrangement and similar molecular weight.120,122 2PA spectra of 140(ql) and 141(ql) in various solvents are shown in Figure 49. In compounds 140(ql) the maximum 2PA cross-section is observed at the short wavelength region of our excitation range while in 141(ql), the 2PA peaks are observed at short to medium wavelengths across our scanning spectral window. Interestingly, 140l exhibits a maximum 2PA cross-section (800 GM) in the low polarity solvent toluene. However, toluene is not the optimum choice upon increasing the number of branches since both 140q and 140 exhibit large values of 2PA crosssections in the more polar THF and acetone. Specifically, chromophore 140 has 2PA cross-section of 1400 GM in acetone. In addition, 141(ql) exhibit the maximum 2PA cross-sections in acetone and THF while the largest 2PA cross-section is observed for 141q in acetone (1420 GM). This data fit perfectly with previous works where has been experimentally observed and/or theoretically predicted that solvents of medium polarity are a good choice for obtaining large 2PA values. 284,285 1000

Toluene THF Acetone Acetonitrile

140l

750

140q 750

500

500

250

(a)

740

760

780

800

820

840

(b)

250

0

0

860

740

760

780

800

820

840

860

1500

2PA cross section   (GM)

2PA cross section   (GM)

1000

140 1000

(c)

500

0 740

760

780

800

820

840

860

Wavelength (nm)

Figure 49. Solvent and branching dependance of 2PA cross for compounds 140(ql).

91

Figure 50. Solvent and branching dependance of 2PA cross for compounds 141(ql).

In order to better evaluate the effect of branching and to assess whether the effect of branches is cooperative, competitive or additive, the 2PA cross-sections of 140(ql) and 141(ql) normalized per branch were investigated. This comparison leads to varied results depending on the series and solvent. In series 140(ql), the 2PA crosssections/branch values decrease or remain approximately constant in quadrupolar and octupolar compounds compared to dipolar ones. The most significant decrease in series 140(ql) was observed in toluene where the cross-section/branch value of 800 GM in 140l decreases to approximately 200 GM for 140q and 140. For 140(ql) in THF and acetone, a nearly additive behaviour was observed meaning that the 2PA cross-sections to each branch are almost the same in the dipolar, quadrupolar and octupolar molecules. Interestingly, in the series of 141(ql), chromophore 141q compared to 141l exhibits a 2PA behaviour that is clearly above the additive behaviour in all solvents except from acetonitrile. This 2PA enhancement is due to a co-operative behaviour of branches and leads to an increase of the 2PA cross-section/branch value of approximately 4, 1.8 and 1.7 times in toluene, THF and acetone, respectively. Unfortunately, this co-operative enhancement is not observed in 141 where a decrease of the 2PA cross-section/branch compared to 141q is observed in all solvents. Besides, in 141, an enhancement of the 2PA spectrum at long wavelengths is observed compared to 141l and 141q, which probably may be due to breaking of symmetry. Although the research works discussed in Chapter 2.2.2115,117,118 as well as theoretical works286 suggest that tripodal strategy would increase the 2PA cross-section 92

due to the co-operation of chromophores, there is no significant enhancement of 2PA cross-section/branch. However, the above comparison of the branched compounds vs. the linear ones should be made over a wide wavelength range. Katan et al.286,287 have shown that a tripodal compound with dipolar branches showed only a slight enhanced 2PA cross-section close to 800 nm compared to its linear counterpart, while a significant enhancement at the higher energy region, close to 700 nm, was observed. Although a 2PA enhancement that is above the additive limit is observed for 141q, the fact that 141 does not exhibit a similar behaviour may be due to the limited spectral window of our experimental system. Finally, another feature that warrants discussion is the comparison of the 1PA and 2PA spectra at half wavelengths for 140 and 141. In dipolar molecules, the same excited state is populated both under 1PA and 2PA, so a similarity of 1PA and 2PA spectra is expected. In the case of tripodal (octupolar) molecules this is not expected according to the excitonic model. In 140, the 2PA spectra exhibit their peak at 760–770 nm, and in 141, at 810–830 nm in all solvents. Both these regions are aprroximately twice the peak wavelengths of 1PA spectra of 140 and 141. This good similarity of the 1PA and 2PA spectra at half wavelengths is an indication of lack or presence of no more than weak coupling among branches. 4.3.5

Quantum chemical calculations The spatial and electronic properties of the parent TPA and chromophores 137–148

were investigated using Gaussian W09 package288 at the DFT level of theory. The initial geometries of molecules 137–148 were estimated by PM3 method implemented in ArgusLab289 and these were subsequently optimized by DFT B3LYP/6-311++G(2d,p) method. The energies of the HOMO and LUMO, their differences and ground state dipole moments were calculated with the DFT B3LYP/6-311++G(2d,p) and are summarized in Table 13.

93

Table 13. Calculated properties of TPA and 137 – 148. Comp.

Symmetry

EHOMO a

ELUMO a



E a

a

group

[eV]

[eV]

[eV]

[D]

TPA

D3

–5.29

–0.90

4.39

0.024

137

D3

–6.53

–2.53

4.00

0.000

138

C3

–6.14

–2.90

3.24

0.227

139

D3

–5.86

–2.39

3.47

0.002

140

D3

–5.80

–2.67

3.13

0.001

141

C3

–5.62

–2.75

2.87

0.221

142

C3

–6.76

–3.80

2.94

5.675

143

C3

–6.49

–3.81

2.68

7.199

144

C3

–6.30

–3.01

3.29

7.603

145

D3

–5.78

–2.84

2.94

0.035

146

C3

–6.05

–3.17

2.88

6.034

147

C3

–5.81

–2.82

2.99

5.199

148

C3

–6.07

–3.13

2.94

11.914

a

Calculated at the DFT B3LYP/6-311++G(2d,p) level.

E = (3.65±3.64) 10-1 + (7.66±1.14) 10-1 EDFT n = 12, s = 1.21 10-1, r = 0.922

Figure 51. Correlation of the electrochemically- and DFT-derived HOMO-LUMO gaps.

The calculated energies of the HOMO/LUMO of 137–148 range from –6.76/–3.81 to –5.62/–2.39 eV and are obviously a function of the structure of the particular chromophore. Both energies correlate tightly with the experimental data obtained by the electrochemical measurements, see for instance correlation of the gaps given in Figure 51. Hence, the used DFT method can be considered as a reasonable tool for the description of electronic properties 94

of 137–148. When going from parent TPA to molecule 137, the HOMO-LUMO gap decreased from 4.39 to 4.00 eV as a result of attaching three cyano groups and generating a push-pull system. Further extension of the -system within the series 137–141 affected the HOMO and LUMO levels as well as the gap in very similar way as observed by the electrochemistry. The lowest HOMO-LUMO gap within this subseries has been calculated for 141 bearing cyano-substituted styryl linker. Further attachment of an additional CN group (140 vs. 145 and 146) resulted in drop of the calculated gap from 3.13 to 2.94 and 2.88 eV. DCV acceptors in chromophores 142–143 impart also strong ICT and reduce the gaps up to 2.94 and 2.68 eV, respectively. A replacement of the terminal 1,4-phenylene moiety in 140 by 2,5-thienylene one in 147 slightly decreases the HOMO-LUMO gap from 3.13 to 2.99 eV in a similar way as observed by CV measurements.

Figure 52. Shape and localization of the HOMO/LUMO in representative molecules 141, 144–145, 147.

The HOMO and LUMO localizations in representative chromophores 141, 144–145, 147 are shown in Figure 52. As expected, the HOMO is localized on the central amino donor and adjacent alternating positions of the TPA, whereas the LUMO is spread over the peripheral cyano acceptor and the adjacent -linker. As can be seen, the LUMO is predominantly localized over one or two particular branche(s), while the third branch is occupied by the LUMO+1. The HOMO as well the HOMO–1 remained on the central amino donor. This is a common feature of tripodal molecules based on TPA.48,118

95

The calculated ground state dipole moments are almost zero for molecules having D3 group of symmetry, whereas noticeable values were obtained for molecules 142–144 and 146–147 having branched and unsymmetrical acceptor moieties (DCV, DCI, 2,4dicyanobenzene and 5(2,4)-(di)cyanothiophene).

4.4 4.4.1

Physical properties of model aminopyridines 149–156 X-ray crystallography of compound 153

Additionally to the other spectral analyses (Chapter 3.29), the structure of 153 was confirmed by single crystal X-ray analysis. Suitable crystals were obtained by slow evaporation of its methanol solution. The ORTEP (50 %) plot shown in Figure 53 confirms the proposed molecular structure of 153. Beside confirmation of the structure, a deeper investigation of ICT character of the compound can also be evaluated by X-ray data. In this respect, the involvement of the particular pyridine rings in the ICT can be assessed by their spatial arrangement and bond length alternation (quinoid character r)290 and aromaticity evaluated by Bird index I6.291,292 The quinoid character and aromaticity of pyridin-4-yl rings were calculated to be within the range of r = 0.009–0.010 and I6 = 94.4–95.9. Unsubstituted benzene has r and I6 equal to 0 and 100, respectively, whereas unsubstituted pyridine has I6 = 85.7. The X-ray analysis indicates that central nitrogen atom has almost planar environment with three nitrogen atoms of pyridin-4-yl substituents, one atom (in ORTEP diagram on Figure 53 represented by atom N4) is always slightly shifted out of that central plane. The values of interplanar angles of the central plane and pyridyl rings were found in the narrow region of 37.7–39.6 °, which is similar to that found for triphenylamine derivatives, e.g. TPPA.20 The r/I6 indicators imply that all pyridine rings possess relatively low/high quinoid/aromatic character and, thus are less involved in the ICT compared for instance with unsubstituted pyridine. On the other hand, a competition of three acceptors for one electron pair should also be considered. Only one particular pyridin-4-yl branch can be involved in the ICT at the same moment (see Figure 53). This lowers quinoid character of the other two, which also reduces the overall averaged quinoid character. These findings are in good accordance with known tripodal triphenylamine derivatives.10

96

Figure 53. ORTEP diagram (50 % probability level) and side view of 153.

4.4.2

Electrochemistry Electrochemical behavior of aminopyridines 149–156 was studied by CV, RDV and

polarography. The acquired data are summarized in Table 14. The measured electrochemical behavior of 149 is consistent with the data reported in the literature.293 The oxidations of 151, 153, 154 and 155 were not observed in the potential window of the given electrode, electrolyte and solvent (up to +1.7 V vs. SCE). The reduction potentials E1/2(red1) were recorded by polarography. The DME (dropping mercury electrode) allowed a cathodic measurement up to –3 V vs. SCE, while on the Pt-electrode it is only –2 V vs. SCE. Oxidation was observed for pyridium salts but this is most likely caused by oxidation of the I– anions. The first reductions, which are reversible one-electron processes, were measured only with the Pt-electrode as interactions of 150, 152 and 154 with the DME were observed.

97

Table 14. Elecrochemical properties of compounds 149–156 Comp.

E1/2(ox1) a [V]

E1/2(red1) a [V]

ELUMO b [eV]

-

EHOMO b [eV] –5.85

149

1.50

150

-

–1.36

-

–2.99

151

-

–2.52

-

–1.83

152

-

–1.62

-

–2.73

153

-

–2.26

-

–2.09

154

-

–0.90

-

–3.45

155

1.08

-

–5.43

-

156

-

–1.11

-

–3.24

-

a

E1/2(ox1) and E1/2(red1) are half-wave potentials of the first oxidation and reduction, respectively. All potentials were recorded in N,N-dimethylformamide containing 0.1 M Bu4NPF6 and are given vs. SCE. b –EHOMO/LUMO = E1/2(ox1/red1) + 4.35 (Ref.294).

When going from 152 to 154, the first reduction potentials decrease by 260 mV, most likely as a result of introducing additional electron withdrawing pyridin-4-yl unit. Quaternization of the pyridine to pyridinium moieties significantly shifted the first reduction potentials to more positive values by 0.9 (151 vs. 152) and 1.36 V (153 vs. 154) which correspond to a significant decrease of the calculated HOMO/LUMO gap in 155 vs. 156 (see below). This clearly reflects the improved electron withdrawing ability and thus enhanced ICT from the central amino donor to peripheral pyridinium acceptors. On the contrary, 152 was reduced at the most negative potential (–1.62 V) among other pyridium salts - 150 (–1.36 V), 154 (–0.90 V) and 156 (–1.11 V). This is most likely given by a facile loss of HI from 152 and formation of an imine/quinnoid structure 152q as shown in Scheme 25. This quinoid cation has also been detected by HR-MALDI-MS as a main peak (Figure 54). In 152/152q, the observed most negative reduction potential reflects enhanced electron density of the central amino donor and subsequent higher saturation of the pyridinium acceptor as expressed by resonant structures shown in Scheme 25.

98

Scheme 25. Expected equilibrium of structures 152 and 152q. DC067_8,0uJ_cal_E1 #1-5 RT: 0.00-0.47 AV: 5 NL: 4.31E7 T: FTMS + p MALDI Full ms [100.00-800.00] 200.11822 100 90 80

Relative Abundance

70 60 50 40 30 20 201.12154 10 200.83260 0 200.0

200.5

201.0

201.5

202.0

202.77391 203.13724 202.5

203.0 m/z

203.90713 203.5

204.0

205.17905 205.52811 204.5

205.0

205.5

NL: 8.68E5

201.12605

100

Relative Abundance

201.75333 202.12489

200.44693

C 12 H 15 N 3: C 12 H 15 N 3 pa Chrg 1

80 60 40 20 0 100

202.12940 203.13276

204.13611

205.13947

206.14282

200.11822

NL: 8.68E5 C 12 H 14 N 3: C 12 H 14 N 3 pa Chrg 1

80 60 40 20 0 200.0

201.12158 202.12493 200.5

201.0

201.5

202.0

203.12829 202.5

203.0 m/z

204.13164 203.5

204.0

205.13500 204.5

205.0

205.5

206.0

Figure 54. Measured (upper) and simulated (lower) HR-MALDI-MS spectra of compounds 152 and 152q.

99

4.4.3

UV/Vis absorption spectra The optical properties of 149–156 were investigated by electronic absorption

spectroscopy measured in DMSO (149 to 154) or MeOH (149 to 156). The measured longestwavelength absorption maxima max and molar absorption coefficients  are given in Table 15. Table 15. Optical properties and computed data of compounds 149–156.

max





[nm(eV)]

[10 M.cm ]

EHOMO c [eV]

ELUMO c [eV]

E c [eV]

[D]

149

267(4.64)sh

1.72

–6.52

–0.66

5.86

5.36

150

273(4.54)

17.29

–7.36

–1.96

5.40

0.58

151

297(4.18)

29.56

–6.35

–1.39

4.95

3.64

23.63/22.97

–7.75

–3.21

4.54

0.16

18.43

–6.30

–1.58

4.72

0.02

30.52/0.62

–7.96

–3.55

4.41

0.06

e

–0.78

d

7.51

d

0.06

e

–2.28

d

5.11

d

2.59

Comp.

152 153

a

333(3.72) /403(3.08)sh 302(4.11)

3

-1 b

334(3.71) 154

c

/404(3.07) 155

363(3.42)

b

-

–8.29

156

420(2.90)

b

-

–7.39

d d

a

Measured in DMSO (c = 2×10-5 M); sh denotes shoulder. bMeasured in MeOH(c = 2×10-5 M) cDFT calculated by

(B3LYP/6-311++G(2d,p)//B3LYP/6-311++G(2d,p)) in DMF. dCalculated by semi-empirical method PM7 implemented in Mopac2012295,296

All of the absorption spectra are dominated by intense CT-bands with the maxima appearing at 267–428 nm. As expected, these CT-bands are red-shifted with the increasing number of pyridin-4-yl units as well as with their replacement by pyridinium acceptors. The length of a conjugation system also shifted the CT bands bathocromically as can be seen in 153 vs. 155 and 154 vs. 156. Chromophore 152 has two particularly developed CT-bands appearing at 333 and 403 nm. The latter corresponds to facile formation of the quinoid structure 152q with extended -conjugated system and stronger electron donor (ICT enhancement). This observation is in accordance with other betaine dyes, especially the Reichardt’s dye used to determine the solvent polarity - ET(30).297,298 The position of the longest-wavelength absorption maxima and the band-width and shape of betaine dyes are strongly solvent-dependent and methanol seems to be exceptional solvent in this respect.299 Hence, the absorption spectra measured in methanol are shown in Figure 55.

100

In contrast to DMSO, the spectra of both 152 and 154 measured in methanol are dominated by intensive low-energy bands appearing at 390 nm. These pronounced bands can be ascribed to a more efficient ICT from the central amino donor to the peripheral pyridinium acceptors and implies higher stabilization of the formed quinoid structure by protic solvents.

Figure 55. UV/Vis spectra of chromophores 149–156 in MeOH.

4.4.4

Quantum chemical calcuations The spatial and electronic properties of 149–154 were investigated by DFT

calculations using B3LYP/6-311++G(2d,p), electronic properties of compounds 155 and 156 were investigated by a semi-empirical calculations PM7 implemented in program Mopac2012®. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), HOMO-LUMO gap (E), and ground state dipole moments () gained by the computational methods used are summarized in Table 15. Only the cationic parts of 150, 152 and 154 were considered in DFT calculations. In case of 156 the methyl groups were replaced by hydrogens to simplify the calculations. Although the calculated energies of the LUMO differ slightly from those obtained by electrochemical measurements (ELUMO = 0.1–1.03 eV), the DFT-derived HOMO-LUMO gap (E) correlate tightly with the energy of the electron transition calculated from the position of the longest-wavelength absorption maxima (1240/max) as shown in Figure 56. Hence, the used DFT calculations are obviously capable of properly describing the trends seen by the optical measurements and can be considered as a reasonable tool for the electronic property description of 149–154. The principal changes are seen in the energies of the LUMO, which reflects the increasing number of pyridine and pyridium acceptors appended to the central amino donor. The calculated HOMO-LUMO gaps decrease from 5.86/5.40 in non methylated chromophores (149, 151 and 153) to 4.72/4.41 eV for methylated products (150, 152 and 154). 101

1240/max = (0.77±0.50) +(0.68±0.10) E

n = 6, r = 0.958, s = 0.126

Figure 56. Correlation between the longest-wavelength absorption maxima and DFT calculated HOMO/LUMO energy gap in compounds 149–154.

The visualizations of the frontier molecular orbitals for 149–154 show acceptorcentered LUMO and donor-centered HOMO, and partial charge separation. This confirms their ICT character (Figure 57). In tripodal molecules 153 and 154, the third pyridin-4-yl branch is occupied by the LUMO+1, the HOMO–1 remained on the central amino donor. This is a common feature of tripodal push-pull molecules observed also in Chapter 4.3.5.

Figure 57. HOMO and LUMO visualizations of chromophores 149–156.

102

As expected, the ground state dipole moment  vanishes with increasing symmetry of the molecule. Tripodal compound 153 proved to be the most symmetrical molecule in the series according to its calculated dipole moment as well as its X-ray crystallographic data (see chapter 4.4.1, Figure 53). 4.4.5

Intercalation Based on a literature knowledge that intercalates of commercially available 149 into

-modification of titanium hydrogenphosphate (Ti(HPO4)2·2H2O) generate significant NLO effect,300,301 intercalation of 149, 151, 153 and 155 was envisaged. Aforementioned compounds were used as guests for intercalates into layered inorganic host based on salts of early transition metals, namely -modification of zirconium hydrogen phosphate (Zr(HPO4)2·2H2O, ZrP), zirconium 4-sulfophenylphosphonate (Zr(HO3C6H4PO3)2·2H2O, ZrSPP) and γ-modification of titanium hydrogen phosphate (Ti(PO4)(H2PO4)·2H2O, TiP). The resulting inorganic-organic hybrids were labeled by a combination of the guest and the host, for instance 149ZrP stands for the intercalate of 149 in - Zr(HPO4)2·2H2O (ZrP). All prepared intercalates were characterized by X-ray diffraction, TGA, IR, electrochemistry, UV/Vis spectroscopy as well as theoretically by DFT calculations. Moreover, second-order susceptibilities (SHG efficiencies) were examined.

Figure 58. Representative intercalation of 153 into the inorganic layered host.

Position and arranegements of the guest molecules 149–156 in the confined space of the inorganic host can be considered as a crucial question regarding the characterization of newly prepared intercalates. In general, they can adopt the following orientation in the interlayer space (see also Figure 58): 103

(i) with the plane of the pyridine rings parallel with the plane of the host layer, either as a one layer of the guest molecules (a "monomolecular" arrangement) or as two layers (a "bimolecular" arrangement) (ii) with the plane of the pyridine ring either perpendicular or tilted with respect to the plane od the host layers. Also in this case the guest molecules can adopt monomolecular or bimolecular arrangement. The gallery heights of the interlayers were determined from basal spacings/interlayer powder X-ray diffraction measurement, and are given in Table 16. In all cases, the value of the interlayer distance is increased on intercalation. This might imply that pyridine ring planes of the guest molecules are not placed parallelly to the host layers. In that case the height of the gallery should be about 2 or 4 Å only. The gallery height in all 149 intercalates (7.48 Å, 6.35, 6.50 Å for 149ZrSPP, 149ZrP and 149TiP, respectively) is equal or even larger than to the van der Waals length of the 149 (6.35 Å). This suggests that the guest molecule can be arranged in the interlayer space with the plane of the pyridine ring perpendicular to the plane of the host layer most probably in an interdigitated manner. Table 16 Basal spacings d (in Å) of intercalates – an overview Intercalate

d [Å]

dg [Å]

a

Accessible 3

volume [Å ]

a

149ZrSPP

24.282

7.48

359.14

151ZrSPP

23.905

7.11

341.04

153ZrSPP

26.390

9.59

460.32

155ZrSPP

33.200

16.40

394.00

149ZrP

12.653

6.35

304.94

151ZrP

13.418

7.12

341.66

153ZrP

12.794

6.50

311.71

155ZrP

18.520

12.52

293.00

149TiP

15.704

6.50

213.98

151TiP

15.156

5.96

195.96

153TiP

15.480

6.28

206.61

Gallery height calculated as dg = d - dl, where d is the basal spacing and dl is the host

layer thickness (16.8, 6.3 and 9.2 Å for ZrSPP, ZrP, and TiP, respectively).

Roughly the same gallery height (7.1 Å) can be observed for the 151ZrSPP and 151ZrP intercalates while it is much smaller for 151TiP (5.9 Å). In all cases the gallery height is smaller than the dimension of 151 along its longest axis (10.5 Å). Therefore, the possibility that the guest molecules are bonded to both layers of the host through their pyridinium groups perpendicularly, forming a kind of pillared structure, can be ruled out. The 104

most probable arrangement appears to be the one in which each guest molecule is bonded to one layer of the host by both pyridinium nitrogen atoms of 151 as shown in Figure 58. High gallery height found for 153ZrSPP (9.6 Å) indicates that this molecule is in an upright position in ZrSPP, whereas in ZrP and TiP (gallery height 6.5 and 6.3 Å, respectively) it is tilted with respect to the host layer plane under an estimated angle of 45°.

1512 cm-1

1634 cm-1

Transmitance / %

APY3 153

MeAPY3 154

153ZrP ZrP-APY3

ZrP ZrP

1800

1600

1400

1200  / cm-1

1000

800

600

Figure 59. Representative IR spectra of 153 and its intercalates.

The nature of interaction of the guest molecules and a host material was determined on the basis of the IR spectra (a representative IR spectrum is given in Figure 59). The peaks in the region from 1150 to 850 cm-1 are generally narrower in intercalates compared to those in the pristine hosts.300 The band at 1231 cm-1 of P-OH found in the spectrum of the original TiP vanishes in the spectra of all three TiP intercalates. Analogous band at 1247 cm-1 in the spectrum of ZrP disappears in the spectra of 149ZrP and 151ZrP; however, this band is retained in the spectrum of 153ZrP, tough, with a lower intensity. In pure 149, NH scissoring 105

band is observed at 1644 cm-1 and peak of ring stretching appears at 1590, 1558, 1504 and 1434 cm-1 (Ref.

302

). In this region, a very broad intensive band at 1649 cm-1 and quite

intensive band at 1535 cm-1 are observed upon N-methylation of 149 leading to 150. These two bands appear also in the 149TiP intercalate. In spectra of 149ZrSPP and 149ZrP a couple of bands at 1650 and 1675 cm-1 and a very broad band at 1540 cm-1 are observed. Moreover, in the spectrum of 149ZrP a very weak peak at 1597 cm-1 is observed which is observed also in the pristine 149. This indicates that in this intercalate a part of the guest remains unprotonated. In the spectrum of 151ZrSPP, the most distinct feature, besides the peaks belonging to the host material, is the existence of peaks at 1624 and 1508 cm -1. These peaks are not present in the spectrum of 151 but appear in the spectrum of 152 at 1654 and 1500 cm-1. In the 151ZrP intercalate, these peaks appear at 1620 and 1506 cm-1 and in 151TiP at 1626 and 1510 cm-1. In the case of 153ZrSPP, the analogous peaks corresponding to methylated (protonated) aminopyridine are less distinct. While the positions of these peaks are at 1634 and 1512 cm-1 in 153, only a weak peak at 1628 cm-1 appears in 153ZrSPP and the second peak is shifted to 1498 cm-1. In the 153ZrP intercalate these peaks are more distinct, with the positions at 1628 cm-1 and 1500-1508 cm-1, nevertheless, a peak of the host material (ZrP) observed at 1614 cm-1 might contribute to the intensity of the peak at 1628 cm-1. Concerning the 155ZrP, the distinct couple of bands at 3588 and 3507 cm-1 present in ZrP which are corresponding to stretching vibrations of the PO–H is replaced by a broad band. The band at 3112 cm-1 corresponding to O–H stretching vibration of water molecules observable in ZrP is broadened in 155ZrP. As the methylpyridinium derivative 156 displays an observable shift of ring stretching bands 1585, 1517, and 1484 cm-1 (present in 155) to 1637, 1581, and 1492 cm-1, the corresponding 155ZrP bands (1637, 1594, and 1492 cm-1), along with the strong suppression P–O–H deformation vibration at 1247 cm-1 (ZrP vs 155ZrP), suggest that 155 is in the intercalate present in somehow protonated form. The C–H deformation vibration bands present at 1335, 1295, 1230, and 1185 cm-1 of 156 are very poorly developed in 155ZrP. In 155ZrSPP, distinct triple of bands at 1636, 1594, 1490 cm-1 (corresponding those in 155ZrP) and less distinct bands at 1328, 1290, 1216 together with a shoulder at 1180 cm-1, reveal virtually the same shape of the intercalate than in case of 155ZrP. Based on these observation it is obvious that 155 is upon intercalation in protonated form. Based on the information provided by IR spectroscopy, we can conclude that aminopyridines 149, 151 and 153 undergo (partial) protonation upon intercalation.

106

Beside the aforementioned measurements in liquid media, the optical properties of 149–156, intercalates were also investigated in the solid-state (representative spectrum is given in Figure 60). Unprotonated 149 has an absorption maximum (max) at 248 nm, whereas methylated 149 showed a maximum at 272 nm. The maxima of all three 149 intercalates are roughly at the same position, around 260 nm. The 149ZrSPP intercalate showed slightly bathochromically shifted max at 262 nm, which reflects that ZrSPP is a host material of the strongest acidity in the interlayer space. 149 protonated by the exposition of this compound to HCl vapours shows a maximum at around 265 nm and its spectrum is similar to those of all three intercalates.

normal. Kubelka-Munk FR(inf.)

149 149TiP 149ZrSPP 150

149ZrP 149 exposed to HCl vapors

1.0

0.8

0.6

0.4

0.2

0.0 300

400

Wavelength / nm

Figure 60. Representative solid state UV/Vis spectra of 149 and its intercalates.

Significant changes in the UV/Vis spectra were observed when going from 151 to methylated 152. Whereas unprotonated 151 showed a single peak at 293 nm, 152 possesses two maxima at 326 and at 392 nm. This is similar to that observed by measurement in DMSO (see above). Compared to the 149 intercalates, the difference between the spectra of all three 151 intercalates is clearly distinguishable. The 151ZrP intercalate has the maximum at the lowest wavelength (297 nm) almost at the same position as the unprotonated 151 guest, with a shoulder at around 320-330 nm. This means that in 151ZrP we can distinguish between the unprotonated and protonated forms of 151. This claim is further supported by the fact that 151 protonated in HCl vapours has a maximum at 321 nm, which is the same region as found for the shoulder in the 151ZrP spectrum. The 151TiP and 151ZrSPP intercalates showed one 107

envelope band with the maxima at 305 and 317 nm, respectively. These bands seem to be superposition of that found for 151 and its protonated form. From these data we can deduce that 151 undergoes partial protonation during intercalation into all three hosts and is being most protonated in ZrSPP (most bathochromically shifted maxima). Thus, the acidity of the hosts increases in the order ZrP < TiP < ZrSPP. In the solid-state, 153 and 154 showed the UV/Vis spectra similar to those observed in methanol (Figure 55) with the maxima appearing at 307 and 323/390 nm, respectively. The 153ZrP intercalate possesses almost the same maximum as 153 with a shoulder at around 325 nm (F). The spectrum of the 153TiP intercalate shows a very broad unstructured band covering the range of 300-320 nm with the maximum reaching the position observed for 153 exposed to HCl vapors (max = 324 nm). The longest-wavelength absorption maximum of 153ZrSPP (max = 323 nm) corresponds tightly to the maximum measured for protonated 153, but in contrast to 154, shows no shoulder. This implies that 153 intercalated into ZrSPP is fully protonated. UV-Vis spectra of 155, 156, 155ZrP and 155ZrSPP clearly reveal that both intercalates contain 155 both in protonated and non-protonated forms, therefore an equilibrium must be considered. This is in discrepancy with the results of the IR spectra measurements, where the bands of the nonprotonated were not found in the IR spectra of 155ZrP and 155ZrSPP. To solve this problem, IR spectrum of the partially protonated 155 (155hp) was prepared (1 mol of 155 with 1.5 mol of HCl – corresponding to exact half protonation of 155). The IR spectrum of 155hp is different from IR spectrum of 155 being more similar to the spectrum of 156. Thus, both the UV-Vis and IR spectra confirm that the 155 guest in 155ZrP and 155ZrSPP is protonated but only partially. Deconvolution of the longest-wavelength absorption maxima

max of 155ZrP and 155ZrSPP revealed two peaks appearing at ∼370 and 450 nm that fit the positions of CT-peaks of 155 and 156. The observed bathochromic shift with Δmax ∼ 80 nm is similar to that observed in the solution and indicates enhanced ICT in both intercalates. In the case of 155ZrP, the shape of the spectrum suggests that the non-protonated form is present in the intercalate in relatively higher amount than in 155ZrSPP. This is yet another proof of the bigger interlayer acidity of the ZrSPP compared with ZrP. When the 155ZrP and 155ZrSPP intercalates were subjected to HCl vapors overnight, their UV-Vis spectra change distinctly being identical to 156. The powder XRD pattern of 155ZrP after the exposure is identical to that before the exposure excluding the deintercalation as an option. The powder XRD pattern of 156ZrSPP after the exposure is identical to that of ZrSPP which means the TPPA guest molecules are deintercalated in an acidic environment. 108

In overall, both IR and UV-Vis spectra imply that acid-base interactions between the pyridine rings and acidic moieties of the host are fundamental for the host/guest interactions during the intercalation process. However, the protonated and non-protonated forms are always present in an equilibrium, which extent depends on each couple host/guest. 4.4.6

NLO properties of 149–154 and their intercalates To create a long-range ordered non-centrosymmetry the investigated chromophores

were embedded into liquid photocomposition of oligoetheracrylate photopolymers, 303 which were photo-solidified by nitrogen 337 nm cw laser with power density 55 W cm-2 at an applied electric field successively increasing up to 4 kV cm. The orientation control was done using a polarized absorption. Typical time kinetics of the fundamental and the SHG signals is shown in Figure 61. The measured principal second-order susceptibility parameters deff jointly with the calculated hyperpolarizabilties (-2;,) of 149–154 and intercalates are listed in Table 17.

FUN, SHG [a.u.]

1.5

FUN=

2.315

SHG=

1.404

1

=

dt=

0.5

0

0

20

40

60

80

0.60647

-3.2 ns

100

120

140

160

180

t [ns]

Figure 61. Representative dependence of the time kinetics of the fundamental (red) and the SHG films. The scale is renormalized for the different scales of 151 for better imaging. One can see some time shift of the corresponding maxima. For other chromophore, the dependences are similar.

The NLO data in Table 17 allow evaluation of the structure-property relationships caused by the chromophore arrangement, N-methylation as well as intercalation. The effect of the chromophore arrangement can easily be assessed on the series 149–154. The linear pushpull aminopyridine 149 showed a SHG response with deff equal to 1.34 pm V-1. An introduction of the second pyridin-4-yl branch as in 151 increased the second-order susceptibility to 1.56 pm V-1. On the contrary, tripodal 153 showed a significantly diminished NLO response with deff = 0.35 pm V-1. This drop reflects the symmetrical arrangement of 153 109

(see chapter 4.4.1) and its very low calculated ground-state dipole moment (Table 15). The extent of the ICT and resulting NLO properties of the heteroaromatic D--A systems can be improved via alkylation. Thus, the comparison of 150, 152, 154 vs. 149, 151, 153 allows evaluation of the effect of the pyridine/pyridinium acceptors. Whereas, the pairs of corresponding chromophores and 152/151 showed slightly improved nonlinearities by a factor of 1.06/1.07, the nonlinearity of 154 is almost three times higher than that found for 153. This observation is most likely given by a significant symmetry loss caused by iodide counter ions, while a synergistic effect of the ICT enhancement via N-methylation should be taken into account as well. In general, the SHG response of aminopyridines decreases in the order of 151>149>153 and 152>150>154, whilst the latter methylated derivatives provided significantly larger NLO response. The calculated hyperpolarizabilities (-2;,) showed very similar trends. The intercalation of 149, 151 and 153 into ZrSPP, ZrP, and TiP is accompanied by their protonation as well organization in the bulk. Whereas the effect of protonation can be considered similar to quaternization, the significant SHG improvement seen for all intercalates over aminopyridines must be elucidated as the impact of their organization in the layered host. The measured SHG responses reflect the acidity of the host, where intercalates with the most acidic ZrSPP showed larger deff than ZrP (except 153). The highest nonlinearities were measured for aminopyridines (149, 151 and 153) intercalated into gamma modification of titanium hydrogen phosphate (TiP). In the TiP intercalates, there is the lowest volume after intercalation which can be explained as the lowest difference between the accessible volume in the interlayer space of the host VH and the volume of the intercalated molecule. The arrangement of the guest molecules in TiP turned out to be the most rigid among all three hosts. In agreement with the state of the art this arguably leads to an increased NLO response.

110

Table 17. Second-order susceptibilities and DFT calculated hyperpolarizabilities of 149–154 and intercalates. Comp.

-1 a

deff [pm V ]

(-2,,) -30

b

[10

a

esu]

149

1.34

1.06

150

1.42

1.37

152

1.67

2.61

153

0.35

0.01

154

1.04

0.13

149ZrSPP

1.78

-

151ZrSPP

1.89

-

153ZrSPP

1.21

-

149ZrP

1.67

-

151ZrP

1.72

-

153ZrP

1.45

-

149TiP

2.01

-

151TiP

2.21

-

153TiP

1.56

-1

Measured in oligoetheracrylate at 1064 (±0.15 pm V ). DFT calculated by (B3LYP/6-311++G(2d,p)// B3LYP/6-311++G(2d,p)) in vacuum at 1064 nm. b

111

5 Conclusions Based on the performed literature research (more than 250 articles), tripodal push-pull molecules having D-(-A)3 arrangement can easily be build up on triphenylamine as a central electron donor. The synthesis of such D-(-A)3 derivatives generaly requires a preparation of the properly substituted triphenylamine (D-part), while the peripheral acceptors are installed often via cross-coupling and condensation methods. Triphenylamine-derived push-pull molecules are currently intensively studied, mostly due to their fluorescent behavior. Their modern applications span two-photon absorbers, metal organic frameworks, semiconductors and also some biological and medicinal applications are known to date. However, except several pilot studies, there was a lack of thorough structure-activity relationships studies, which opened a field for my own investigations. The aforementioned knowledge gained from the literature enabled a design and synthesis of three series of chromophores. The common featrure of all the series is the presence of nitrogen atom as a central donor connected via -linker with peripheral cyano- or pyridine-based acceptors. The first series of compounds 137–148 was designed to evaluate structure-property relationships in order to tune mostly 2PA properties of tripodal TPA-based chromopores. Linear, quadrupolar and tripodal chromophores 140(ql) and 141(ql) were designed to address branching and solvent effects on (non)linear optical properties. The last series of compounds 149–155 was prepared to verify the hypothesis that pyridine push-pull molecules are well-suited organic compounds for intercalation into layered materials, in order to obtain novel inorganic-organic hybrid materials with enhanced optoelectronic properties. DSC measurements of compounds 137–148 revealed a vast influence of the acceptor part on their thermal properties with the measured Tm and Td ranging within the limits of 84– 343 and 176–477 °C, respectively. (Poly)cyanophenyl- and imidazole-based acceptors turned out to be the most thermally stable chromophores within the whole series. On the other hand, dicyanovinyl moiety especially in a combination with acetylenic -linker (e.g. 143) decreased the thermal stability significantly. When comparing with other known tripodal molecules, compounds 137–148 proved to be thermally stable above the average. The electrochemical properties (HOMO and LUMO levels and band gaps) were primarily affected by a type of the peripheral acceptor. Length and composition of the -linker as well as its planarity have also a considerable impact. Using these structural changes as a tool, the electrochemical HOMO-LUMO gap could be finely tuned by almost 1 V (3.50 to 2.54 V). 112

One

photon

absorption

and

emission

properties

studied

by

electronic

absorption/emission spectra revealed well developed CT-bands appearing between 339/377 and 470/611 nm, respectively. Hence, the optical tuning could be carried out within the range of 130/230 nm. Quantum yields range from 0.29–0.69 without any distinguishable trends. The two photon absorption properties of 137–148 were measured by two-photon excited fluorescence spectroscopy within the spectral range 750 to 850 nm. A critical assessment has been carried out within/across the particular series of chromophores in order to evaluate structure-property relationships. Extension of the -system and replacement of acetylenic by more polarizable olefinic units leads to a significant increase of 2PA activity. Hence, chromophore 141 bearing cyano substituted styryl linker showed the most enhanced NLO activity within the whole series. An attachment of aromatic acceptors bearing two CN groups (145 and 146) as well as strongly withdrawing DCV units in 142 and 143 did not bring any further increase of the 2PA cross-section compared to 141. A similar conclusion can be made for heterocyclic cyano acceptors such as DCI and 5(3,4)-(di)cyanothiophene. Hence, electron withdrawing behavior of the appended acceptor turned out to be negligible feature affecting the measured 2PA activity. The planarity and polarizability of the -conjugated path seem to be the most crucial structural aspects affecting 2PA activity of tripodal molecules. The DFT calculate HOMO and LUMO levels and their differences correlates tightly with the linear properties measured by electrochemistry and absorption/emission spectra. Wheras is the HOMO localized on the central amino donor, the branches are occupied by LUMOs. A study of the branching and solvent effects on photophysical and 2PA properties of triphenylamine molecules was performed for the molecules 140(ql) and 141(ql). Compounds 140 and 141 were chosen for their kown NLO activity and for the relative easy preparation of their linear (l) and quadrupolar (q) analogues. The photophysical properties showed a dipolar nature of the emitting state in the tripodal molecules, a behaviour resembling that of the linear dipolar molecules. Smallish red-shifts of the absorption maxima of 140(ql) and 141(ql) imply a presence of only neglectible coupling among branches. The investigation of the 2PA properties has shown that the 2PA cross-section of the branched compounds increases compared to that of the dipolar ones. In some cases, depending on the solvent used and molecule, this increase is higher than what was expected based on an additive behaviour of the branches, implying a co-operative effect. In the other cases co-operative effect was barely observable. Surprisingly, the quadrupolar molecules showed better performance than their tripodal analogues. The highest 2PA cross-section was observed in solvents of medium 113

polarity where 2PA cross-section of 1420 GM was measured for the quadrupolar molecule 141q in acetone. The series of chromophores 149–156 having various spatial arrangements was targeted to study the feasibility of their incorporation into the layered inorganic materials (modification of zirconium hydrogen phosphate, zirconium 4-sulfophenylphosphonate, and

-modification of titanium hydrogen phosphate). The prepared inorganic-organic hybrids were further investigated as ordered materials for nonlinear optics. The chromophores 149–156 and their intercalates were investigated as second-order nonlinear

optical

materials.

The

measured

as

well

as

calculated

optical

susceptibilities/hyperpolarizabilities have shown interesting structural-activity trends. The SHG response generally follow the order of quadrupolar > linear > tripodal (151 > 149 > 153 and 152 > 150 > 154). Quaternization along with protonation, enhance the SHG response significantly. This also holds true for intercalation into layered materials of various acidity, where ZrSPP and TiP proved to be more efficient acids than ZrP. Compared to ZrSPP and ZrP, the TiP intercalates have more tightly arranged aminopyridine molecules and showed higher SHG response. Furthermore, a facile synthetic pathway has been developed to novel tripodal tris(pyridin-4-yl)amine (153). Its structure was unambiguously confirmed by single crystal X-ray analysis, which revealed almost perfectly planar environment of all three peripheral nitrogen

atoms.

The

fundamental

properties

of

149–156

were

investigated

by

electrochemistry, UV/Vis absorption spectra and were completed with DFT calculations. It was demonstrated that with increased number of the pyridin-4-yl acceptor units, the HOMO-LUMO gap decreases steadily by more than 1 eV and the longest-wavelength absorption maxima shifts bathochromically (max ~ 30 nm). N-Quaternization, which takes place exclusively on the peripheral pyridines even in the presence of unprotected –NH2 and –NH– groups, caused further reduction of the HOMO-LUMO gap and red-shifts the CTband. Structural analysis of 150, 152, 154 and 156 compounds revealed facile formation of the quinoid structures, which significantly affected their electrochemical and optical properties. In overall, this dissertation work showed several new push-pull molecules, some new strategies towards their property tuning and applications in nonlinear optics. The property tuning has been accomplished by the following features: -

variation of the peripheral acceptor

-

variation of the -system 114

-

planarity

-

variation of the chromophore arrangement

-

variation of the environment

-

intercalation

-

protonation

Considering all the obtained results and their interpretations, I believe that this work could be treated as a useful guide in designing/tuning n-podal push-pull molecules with central donor and peripheral acceptors. Scientific outcomes of this dissertation work were published in the following research articles (the reprints are presented as annexes): 1. Melánová K., Cvejn D., Bureš F., Zima V., Svoboda J., Beneš L., Mikysek T., Pytela O., Knotek P., Dalton Trans., 2014, 43, 10462–10470. 2. Cvejn D., Michail E., Polyzos I., Almonasy N., Pytela O., Klikar M., Mikysek T., Giannetas V., Fakis M., Bureš F., J. Mater. Chem. C, 2015, 3, 7345-7355. 3. Cvejn D., Michail E., Seintis K., Klikar M., Pytela O., Mikysek T., Almonasy N., Ludwig M., Giannetas V., Fakis M., Bureš F., RSC Adv., 2015, submitted. 4. Bureš F., Cvejn D., Melánová K., Beneš L., Svoboda J., Zima V., Pytela O., Mikysek T., Růžičková Z., Kityk I. V., Wojciechowski A., AlZayed N., J. Mater. Chem. C, 2015, accepted (DOI: 10.1039/C5TC03499J).

115

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Annexes All the supplementary informations and native data of the experiments are given in the enclosed articles.

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ÚDAJE PRO KNIHOVNICKOU DATABÁZI Název práce

D--A Chromophores with Nonlinear Optical Properties

Autor práce

Daniel Cvejn

Obor

Organická chemie

Rok obhajoby

2016

Vedoucí práce

doc. Ing. Filip Bureš, Ph.D. Tato práce se zabývá designem, syntézou, charakterizací a fyzikálně-chemickými

vlastnostmi

push-pull

chromoforů

pro

dvoufotonovou absorbci a interkalaci. Cílové chromofory byly připraveny s využitím moderních cross-coupling reakcí a jejich struktura Anotace

a vlastnosti byly zkoumány pomocí NMR, HR-MALDI-MS, IČ spektroskopie,

rentgenové

analýzy,

elektrochemie,

UV/Vis

absorpční/emisní spektroskopie, diferenční skenovací kalorimetrie, 2PA fluorescenční spektroskopií, generací druhé harmonické a DFT výpočty. Byly vyvozeny vztahy typu struktura-vlastnosti. Klíčová slova

Push-pull, trifenylamin, cross-coupling, nelineární optika, dvoufotonová absorbce, interkalace

129