THE LIQUID CRYSTALS BOOK SERIES

CHEMISTRY OF DISCOTIC LIQUID CRYSTALS FROM MONOMERS TO POLYMERS

Sandeep Kumar

CRC Press

Taylor &Francis Group Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

Contents xiii xv

Preface Author Chapter 1 Introduction Self-Organization of Molecules and Liquid Crystals 1.1.1 Liquid Crystals as an Intermediate Phase (Mesophase) of Matter 1.2 Brief History of Liquid Crystals 1.3 Classification of Liquid Crystals 1.4 Lyotropic Liquid Crystals 1.5 Thermotropic Liquid Crystals 1.6 Calamitic Liquid Crystals 1.6.1 Nematic Phase 1.6.2 Chiral Nematic Phase 1.6.3 Smectic Phases 1.6.4 Smectic C* Phase 1.6.5 Ferro-, Antiferro-, and Ferrielectric Chiral Smectic C Phases 1.7 Bent-Core Liquid Crystals 1.8 Discotic Liquid Crystals 1.8.1 Structure of the Discotic Mesogens 1.8.2 Characterization of Discotic Liquid Crystal Phases 1.9 Structure of the Nematic Phases of Discotic Mesogens 1.10 Smectic Phases of Discotic Mesogens 1.11 Columnar Phases of Discotic Mesogens 1.11.1 Hexagonal Columnar Mesophase 1.11.2 Rectangular Columnar Mesophase 1.11.3 Columnar Oblique Mesophase 1.11.4 Columnar Plastic Mesophase 1.11.5 Columnar Helical (H) Phase 1.11.6 Columnar Lamellar Mesophase 1.113 Columnar Square (Tetragonal) Phase 1.12 Cubic Phase 1.13 Alignment of Discotic Liquid Crystals 1.13.1 Alignrnent Control Techniques for Discotic Nematic Liquid Crystals 1.132 Alignment Control Techniques for the Discotic Columnar Phase 1.13.2.1 Planar Alignment of Discotic Columnar Phase 1.13.2.2 Homeotropic Alignment of Discotic Columnar Phases 1.13.2.3 Alignment of Discotic Liquid Crystals in Pores References 1.1

Chapter 2 Monomeric Discotic Liquid Crystals 2.1 Benzene Core 2.2 Naphthalene Core 2.3 Phenanthrene Core

1 1 2 4 6 7 10 10 11 11 12 14 14 15 18 19 20 20 22 22 23 25 26 26 26 27 28 28 29 30 32 33 38 41 42 49 49 74 76

viii

Contents 2.4 Anthraquinone Core 2.4.1 Rufigallol-Hexa-n-Alkanoates 2.4.2 Octa-Alkanoyloxy-9,10-Anthraquinones 2.4.3 Hexa-n-Alkoxyrufigallols 2.4.4 Mixed Tail Hexaalkoxyrufigallols 2.4.5 Mono-Hydroxy-Pentaalkoxyrufigallols 2.4.6 Rufigallol-Based Discotic-Calamitic Hybrids 2.4.7 Rufigallol-Based Discotic Metallomesogens 2.5 Pyrene Core 2.6 Triphenylene Core 2.6.1 Symmetrical Triphenylene Hexaethers 2.6.2 Symmetrical Triphenylene Hexaesters 2.6.3 Unsymmetrical Triphenylene Derivatives 2.6.4 Hydroxy-Alkoxy-TPs 2.6.5 Discotics Derived from Hydroxy-Alkoxy-TPs 2.6.6 Discotics Derived from Hexaalkoxy-TPs 2.6.6.1 Electrophilic Aromatic Substitution in Hexaalkoxy-TPs 2.6.6.2 Chromium-Arene Complex of Hexaalkoxy-TPs 2.6.7 Thermal Behavior of Unsymmetrical Triphenylene Discotics 2.6.8 Discotics Derived from 2,3,6,7,10,11-Hexabromo-TP 2.6.8.1 Hexathioethers and Selenoethers 2.6.8.2 Hexaalkynyltriphenylenes 2.6.8.3 Hexaphenyltriphenylenes 2.6.9 Trisubstituted Triphenylene Discotics 2.6.10 Physical Studies 23 Perylene Core 2.7.1 3,4,9,10-Tetra-(n-Alkoxycarbony1)-Perylenes 2.7.2 Perylene Bisimides 2.8 Dibenzo[g,p]chrysene Core 2.9 Dibenzo[fg,op]naphthacene Core 2.10 Truxene Core 2.11 Decacyclene Core 2.12 Hexabenzocoronene Core 2.12.1 Hexa-Cata-Hexabenzocoronene 2.12.2 Larger Discotic Cores (Graphenes) 2.13 Macrocyclic Cores 2.13.1 Tribenzocyclononatriene Core 2.13.2 Tetrabenzocyclododecatetraene Core 2.13.3 Metacyclophane 2.13A Phenylacetylene Macrocycles Miscellaneous Arornatic Cores 2.14.1 Indene and Pseudoazulene: Discotics without Flexible Aliphatic Chains 2.14.2 Benzo[b]triphenylene Core 2.14.3 Tetraphenylenes 2.14.4 Tetrabenzo[a,c,h,Aanthracene Core 2.14.5 Helicene Discotics 2.14.6 Tetrahedral and Other Low Aspect Ratio Organic Materials 2.15 Triazine Core 2.16 Phenazines

78 79 80 81 82 83 86 89 90 94 95 101 102 109 113 119 119 123 123 138 138 140 141 142 143 143 143 145 151 156 162 165 167 183 184 186 186 189 191 193 198 198 198 200 200 202 203 203 219

Contents

ix 2.16.1 Bisphenazines 2.16.2 Dibenzophenazines 2.16.3 Dibenzoquinoxaline 2.17 Hexaazatriphenylene Core 2.17.1 Hexaazatrinaphthylene 2.18 Heterotruxenes 2.18.1 Oxatruxene 2.18.2 Thiatruxene 2.18.3 Triindole 2.19 Tricycloquinazoline Core 2.20 Porphyrin Core 2.20.1 ß-Substituted Porphyrin Derivatives 2.20.2 Meso-Substituted Porphyrins 2.20.3 Miscellaneous Porphyrin Derivatives 2.21 Porphyrazine Core 2.22 Phthalocyanine Core 2.22.1 Octaalkoxymethyl-Substituted Phthalocyanines 2.22.2 Octaalkoxy-Substituted Phthalocyanines 2.22.3 Octaalkyl-Substituted Phthalocyanines 2.22.4 Octathioalkyl-Substituted Phthalocyanines 2.22.5 Octathiaalkylmethyl-Substituted Phthalocyanines 2.22.6 Peripheral Octaalkoxyphenyl- and Alkoxyphenoxy-Substituted Phthalocyanines 2.22.7 Octaalkyl Esters of Phthalocyanine 2.22.8 Non-Peripherally Substituted Octaalkyl and Octaalkoxymethyl Phthalocyanines 2.22.9 Non-Symmetrical Octa-, Hepta-, Hexa-, and Penta-Substituted Phthalocyanines 2.22.10 Unsymmetrical Non-Peripheral Phthalocyanines 2.22.11 Tetraalkoxy-Substituted Phthalocyanines 2.22.12 Tetrathiaalkyl- and Tetraalkylthiamethyl-Substituted Phthalocyanines 2.22.13 Tetraesters of Phthalocyanine 2.22.14 Crown-Ether-Substituted F'hthalocyanines 2.22.15 Core-Extended Macrodiscotic Phthalocyanines 2.22.16 Subphthalocyanines 2.22.17 Miscellaneous Compounds Structurally Related to Phthalocyanines Miscellaneous Discotic Metallomesogens 2.23.1 13-Diketonate Complexes 2.23.2 Tri- and Tetraketonate Complexes 2.23.3 Dithiolene Complexes 2.23.4 Dioximato Complexes 2.23.5 Cyclic Pyrazole—Metal Complexes 2.23.6 Dibenzotetraaza[14]annulene Complexes 223.7 Tonic Metallomesogens 2.23.8 Bis(salicylaldirninato)metal(H) Cornplexes 2.23.9 Schiff Base Lanthanide and Actinide Complexes Miscellaneous Heterocyclic Cores /24.1 Benzopyranobenzopyran-Dione 2.24.2 Benzotrisfuran

220 221 224 225 228 233 233 233 235 237 242 243 248 257 261 267 268 270 273 274 276 276 279 281 283 286 287 287 289 290 292 295 297 297 298 300 301 302 303 304 305 305 307 307 307 308

Contents 2.24.3 Pyrillium and Dithiolium Salts 2.24.4 Bispyran and Bisthiopyran 2.24.5 Cyclotriphosphazines 2.24.6 Tetraoxa[8]circulene 2.24.7 Tetraazopyrene, Benzo[c]cinnoline, and Dibenzo[c,e][1,2] thiazine 2.24.8 Tristyrylpyridine 2.24.9 Tristriazolotriazine 2.24.10 Benzotriimidazole 2.24.11 Triphenylamine Core 2.25 Non-Aromatic Cores 2.25.1 Cyclohexane 2.25.2 Glucopyranose 2.25.3 Azamacrocycles References Chapter 3 Discotic Dimers

311 312 312 313 313 316 317 317 319 319 319 321 322 323 361

3.1 Benzene-Based Discotic Dimers 3.1.1 Alkynylbenzene-Based Discotic Dimers 3.2 Scylloinositol Dimer 3.3 Discotic Dimers Derived from Pyranose Sugars 3.4 Rufigallol-Based Discotic Dimers 3.5 Triphenylene-Based Discotic Dimers 3.5.1 Symmetrical Triphenylene Discotic Dimers 3.5.2 Hydrogen-Bonded Symmetrical Triphenylene Discotic Dimers 3.5.3 Nonsymmetrical Triphenylene Discotic Dimers 3.6 Cyclotetraveratrylene Dimer 3.7 Phthalocyanine-Based Discotic Dimers 3.7.1 Phthalocyanine Dimers Connected through Flexible Spacers 3.7.2 Phthalocyanine Double-Deckers 3.8 Porphyrin Double-Deckers 3.9 Hexabenzocoronene-Based Dimers References

361 362 366 366 367 368 368 378 379 380 381 381 382 386 388 391

4.1

395 395 399 399 400 403 403 408 409 410 412

Discotic Trimers 4.1.1 Triphenylene-Based Discotic Trimers 4.1.2 Trisaccharide Discotics 4.1.3 Multiyne-Based Discotic. Trimers 4.1.4 Phthalocyanine and Porphyrin Discotic Trimers 4.1.5 Hexabenzocoronene Discotic Trimers 4.2 Discotic Tetramers 4.3 Discotic Pentamers 4.4 Discotic Hexamers 4.5 Star-Shaped Discotic Heptamers References

Contents Chapter 5

Chapter 6

xi Discotic Polymers

415

5.1 5.2 5.3 5.4

Benzene-Based Discotic Polymers Alkynylbenzene-Based Discotic Polymers Rufigallol-Based Main-Chain Discotic Polymers Triphenylene-Based Polymers 5.4.1 Triphenylene-Based Side-Chain Polymers 5.4.2 Triphenylene-Based Main-Chain Polymers 5.4.3 Triphenylene-Based Discotic Elastomers 5.4.4 Triphenylene-Based Hyperbranched Polymer 5.4.5 Triphenylene-Based Discotic Compensation Films 5.5 Cyclotetraveratrylene-Based Polymers 5.6 Phthalocyanine-Based Polymers 5.7 Hexabenzocoronene-Based Polymers References

415 418 421 422 423 431 435 436 436 437 438 441 443

Perspectives

447

6.1

447 447 449 450 452 452 453

Discotics for Wide Viewing Displays 6.1.1 Optical Compensation Films for Liquid Crystal Displays 6.1.2 Discotic Nematic Materials as Active Component in LCDs 6.1.3 Thin Film E-Polarizer from Discotic Nematic Lyo-Mesophases 6.2 Discotics for High-Quality Carbon Products 6.2.1 Carbonaceous Mesophase 6.2.2 Carbon Nanostructures from Discotics 6.3 Discotic Liquid Crystals as Materials for a New Generation of Organic Electronics 6.3.1 One-Dimensional Electrical and Photoconductivity in DLCs 6.3.2 Steady-State Photoconductivity 6.3.3 Charge-Carrier Mobility in Columnar Phases 6.3.3.1 Time-of-Flight Technique 6.3.3.2 Pulse-Radiolysis Time-Resolved Microwave Conductivity Technique 6.4 Discotic Solar Cells 6.5 Discotic Liquid Crystals as Organic Light-Emitting Diode Materials 6.6 Discotic Field Effect Transistors References

454 455 459 460 461 463 476 478 481 482