Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

2.3. [4 + 4] Cycloadditions 1058 2.4. Photocycloadditions of Aromatic Compounds 1058 2.4.1. Benzene Derivatives 1058 2.4.2. Condensed Aromatic Compounds 1060 3. Photochemical Rearrangements 1061 4. Cyclizations 1064 4.1. Pericyclizations 1064 4.2. Norrish−Yang Reaction 1066 5. Photochemical Extrusion of Small Molecules 1067 6. Photochemical Electron Transfer 1068 6.1. Photochemical Electron-Transfer Reactions with a Catalytic Sensitizer 1068

Photochemical Reactions as Key Steps in Organic Synthesis

Direct asymmetric catalytic aldol reactions have been successfully performed using aldehydes and unmodified ketones together with commercially available chiral cyclic secondary amines as catalysts Structure-based catalyst screening identified l-proline and 5,5-dimethyl thiazolidinium-4-carboxylate (DMTC) as the most powerful amino acid catalysts for the reaction of both acyclic and cyclic ketones as aldol donors with aromatic and aliphatic aldehydes to afford the corresponding aldol products with high regio-, diastereo-, and enantioselectivities Reactions employing hydroxyacetone as an aldol donor provide anti-1,2-diols as the major product with ee values up to >99% The reactions are assumed to proceed via a metal-free Zimmerman−Traxler-type transition state and involve an enamine intermediate The observed stereochemistry of the products is in accordance with the proposed transition state Further supporting evidence is provided by the lack of nonlinear effects The reactions tolerate a small amount o

https://www.scripps.edu/barbas/pdf/Sakthivel01JACS.pdf

Amino Acid Catalyzed Direct Asymmetric Aldol Reactions: A Bioorganic Approach to Catalytic Asymmetric Carbon-Carbon Bond-Forming Reactions

Color tuning and switching of the solid-state luminescence of organic materials are attractive subjects for both the fundamental research and practical applications such as optical recording. We report herein cyanostilbene-based highly luminescent molecular sheets which exhibit two-color fluorescence switching in response to pressure, temperature, and solvent vapor. The origin for the multistimuli luminescence switching is the two-directional shear-sliding capability of molecular sheets, which are formed via intermolecular multiple C−H···N and C−H···O hydrogen bonds. The resulting two distinctive crystal phases are promoted by different modes of local dipole coupling, which cause a substantial alternation of π−π overlap. These changes can be directly correlated with the subsequent intermolecular excitonic and excimeric coupling in both phases, as demonstrated by an in-depth theory-assisted spectroscopic and structural study. Finally, we have prepared a first device demonstrator for rewritable fluorescent ...

Multistimuli Two-Color Luminescence Switching via Different Slip-Stacking of Highly Fluorescent Molecular Sheets

Disc-shaped objects can be induced to form columnar assemblies whether their scale is tens of Angstroms (molecular), tens of nanometers (macromolecular or supramolecular), hundreds of nanometers (colloidal) or tens of microns (‘manufactured’ platelets). The last couple of years have seen rapid progress in the development of conducting columnar systems and in controlling the orientation of discotic mesophases. The first serious commercial development has also emerged. Fuji Film Company has perfected and marketed optical compensating films based on cross-linked nematic discogens with controlled hybrid orientation.

Discotic liquid crystals 25 years on

Compact and simple nondiscoid mesogens, trialkoxybenzoic anhydrides 2−11 ((RO)3C6H2−CO−O−CO−C6H2(OR)3, R = C2H5, n-C3H7, n-C4H9, n-C6H13, n-C8H17, n-C10H21, n-C12H25, n-C14H29, n-C16H33, and (S)- and (R)-3,7-dimethyloctyl) were designed and synthesized, and their superstructures were investigated by polarized light microscopy, differential scanning calorimetry, calculation (MM2 and AM1), circular dichroism spectroscopy, and X-ray diffraction. As the result, in the cases of 5−9 and 11, the half-disk molecules in the liquid crystal phases were self-assembled by the dipole−dipole interaction between their carbonyl groups to a column in which the molecules were piled up in an alternately antiparallel manner, and the columns were interdigitated each other. The observed interdigitations were highly directional in the perpendicular direction to the column axis. In the case of compound 11 which has (S)- or (R)-3,7-dimethyloctyl groups, a helical organization of the molecules in the column was estimated from the p...

Novel superstructure of nondiscoid mesogens: uneven-parallel association of half-disk molecules, 3,4,5-trialkoxybenzoic anhydrides, to a columnar structure and its one-directionally geared interdigitation.

The aldol reaction of the boron enolate bearing the titled chiral auxiliary proceeded with high face selectivity.

New Chiral Auxiliary; 4,5-Diphenyl-1-methyl-2-imidazolidinone. Its Utility in Highly Enantioselective Aldol Reaction

Intramolecular diastereoselective [4 + 4] photocycloadditions of acyclic imides 1a and 1b possessing anthracene and naphthalene moieties were carried out in the solid state and in solution. For 1a, novel reversal of diastereoselectivity was observed on changing the reaction phase. The diastereomeric excess was changed from −60% de in the solid state at 60 °C to 70% de in acetone at −78 °C. Almost 100% de was observed for the solid-state photocycloaddition of 1b. The reactivity of 1a in the solid state was discussed based on its single crystal X-ray analysis.

Diastereoselective intramolecular [4 + 4] photocycloaddition reaction of N-(naphthylcarbonyl)anthracene-9-carboxamides: temperature effects and reversal of diastereoselectivity

Guest inclusion abilities of two rotamers, anti- and syn-N,N′-bis-(2-tert-butylphenyl)naphthalene-1,4,5,8-tetracarboxylic diimides 1 and 2, were investigated. Rotamers 1 and 2 were synthesised from 2-tert-butylaniline and naphthalene-1,4,5,8-tetracarboxylic dianhydride and separated by conventional column chromatography on silica gel. Recrystallisation of 1 from chloroform in the presence of a guest molecule (3 mole equivalents) was performed, and 15 guest molecules were included with a variety of host∶guest ratios, 1∶1 (chloroform, pyridine, 4-picoline, benzene, quinoline, diphenylacetylene, naphthalene, and p-toluidine), 1∶2 (phenol, 3-ethylphenol, 4-methoxyphenol, indole, 5-methylindole, and tetrathiafulvalene), and 1∶4 (benzothiazole). In contrast, 2 showed no inclusion of guest molecules under the same conditions as those applied to 1. In order to investigate the intermolecular interaction in the crystalline state of 1, 2 and 1·(indole)2, X-ray diffraction of single crystals was measured and these structures were compared.

Shigeo Kohmoto

Papers

Novel superstructure of nondiscoid mesogens: uneven-parallel association of half-disk molecules, 3,4,5-trialkoxybenzoic anhydrides, to a columnar structure and its one-directionally geared interdigitation.

New Chiral Auxiliary; 4,5-Diphenyl-1-methyl-2-imidazolidinone. Its Utility in Highly Enantioselective Aldol Reaction

Diastereoselective intramolecular [4 + 4] photocycloaddition reaction of N-(naphthylcarbonyl)anthracene-9-carboxamides: temperature effects and reversal of diastereoselectivity

Difference in guest-inclusion abilities of anti- and syn-rotamers

Enantioselective intramolecular aromatic [4 + 4] photocycloaddition in crystalline state: parameters for reactivity.