Shunsuke Takenaka

The Substituent Effect on the Thermal Stability of the Smectic A Phase in para- Phenylene Systems Incorporating Ester Linkages

Abstract Summary: The thermal properties of 4-Z-phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxy- phenyl 4-(4-Z-benzoyloxy) benzoates (2), 4-(4-octyloxybenzoyloxy) phenyl 4-Z-benzoates (3) and 4- octyloxyphenyl 4-(4-Z-phenoxycarbonyl)benzoates (4) have been examined, where the substituents (Z) are halogens, alkoxy, alkyl, formyl, acetyl, cyano, and nitro groups, etc. The smectic properties are strongly dependent on the orientation of the ester linkages. Compounds 1 and 4 having alkoxy and alkyl groups tend to show smectic A and C phases. Compounds 2 and 3 are intrinsically poor in smectic properties, and only a smectic C phase is formed by the long-alkoxy and alkyl derivatives. Throughout the compounds, the thermal stability of the smectic A phase is strongly dependent on the electrostatic nature of the substituents; that is, both electron-donating substituents such as the methoxy and methyl groups and electron-withdrawing ones such as the cyano and nitro groups, steeply lower the smectic A therma...

Liquid crystalline properties of some compounds having a perfluoroalkyl group

Abstract The paper describes the liquid crystalline properties of 2-(n-perfluoroalkyl)ethyl para-, meta-, and/or ortho-substituted benzoates, and some related compounds. Most of the ortho and/or meta-substituted derivatives show a smectic B phase, while the para-substituted ones are non-mesogenic. When the substituent is a nitro or a cyano group, many derivatives show a smectic A, as well as a B phase. The corresponding 4-trans-alkylcyclohexanecarboxylates are non-mesogenic. Meta- orpara-substituted phenyl ω-hydroperfluoroalkanoates are also non-mesogenic. From these results, we conclude that in order to show liquid crystalline properties for the present systems, the substituents at meta and/or ortho positions, orientation of the ester group, and the rigid perfluoroalkyl group are very important. X-ray study indicated that the smectic A and B phases for polar liquid crystals have a partially bilayer and bilayer arrangements, respectively. The smectic B phase for non-polar liquid crystals have a monolayer arrangement. Thermal motion around the perfluoroalkyl group is assumed to be almost frozen in both phases.

Thermal and X-ray diffraction studies of liquid crystals incorporating a perfluoroalkyl group

Thermal properties of perfluoroalkyl 4-(4-alkoxybenzoyloxy)benzoates (1), 4-(4-alkoxyphenoxycarbonyl)benzoates (2), and 4-trans-(4-alkoxyphenoxycarbonyl)cyclohexanecarboxylates (3) have been examined, and the layer spacings of the smectic A and C phases were obtained by X-ray diffraction experiments. The perfluoroalkyl group facilitates the formation of smectic A and C phases (SA and SC, respectively). For compound 1, the molecular arrangements in the SA and SC phases are concerned with the chain length of the alkoxy group, that is the layer spacing of the SA phase agrees with the calculated molecular length when the alkoxy group is the octyloxy group, and exceeds it when it is the butoxy one. The derivatives of compound 2 show only the SA phase, having a somewhat interdigited arrangement. Compound 3 preferentially forms the SA phase. The results are discussed in terms of the molecular structures and local interactions.

Thermal Properties of 4-Alkoxyphenyl 3,4-Di(4-alkoxybenzoyloxy)benzoates

Abstract A homologous series of 4-alkoxyphenyl 3,4-di(4-alkoxybenzoyloxy)benzoates has been prepared. All the members (from the ethoxy to nonyloxy homologs) show a nematic phase having a fine schlieren texture, and the nonyloxy homolog also shows a smectic A phase having a fine fan texture. The plot of the nematic-isotropic transition temperatures against the carbon number of the alkoxy chains shows a remarkable even-odd effect. The mesophases have an affinity with the nematic and smectic A phases of the usual rod-like liquid crystals. The nematic phase is highly viscous. The thermal properties are discussed in terms of the molecular structure. A geometrical boundary between rod-like and discotic liquid crystals has been discussed.

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH3, CH3, OC8H17, C8H17, halogens, CF3, OCF3, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.

THE TRANS-1,4-CYCLOHEXYLENE GROUP AS A STRUCTURAL FRAGMENT IN LIQUID CRYSTALS

In this review the effect on physico-chemical and electro-optical properties of the introduction of the trans-1,4-cyclohexylene fragment into the molecular core of liquid crystals is discussed, rationalized in terms of existent theories, and compared with the effect of other well-known molecular fragments.

The Discotic Mesophases of 1,3,5-Trisubstituted Benzenes

Abstract Some homologous series of 1,3,5-trisubstituted benzenes have been prepared. A homologous series of 1,3,5-tri-(4-alkoxyphenoxycarbonyl)benzenes (the hexyloxy to decyloxy homologs) give rise to discotic mesophases having a nematic-like texture.

Halogenation in achiral liquid crystals: terminal and linking substitutions

The effect on the physico-chemical properties of achiral liquid crystals of introducing halogen atoms into their terminal and linking groups is discussed and rationalized in terms of existing theories; a comparison is made with the corresponding hydrogenated and other well-known groups.

Large Third-Order Optical Nonlinearities of a Croconium Dye in Tetrahydrofuran Solution and in Poly(methyl methacrylate) Coating Films Measured Using Resonant Femtosecond Degenerate Four-Wave Mixing Technique

The third-order optical nonlinearities of a croconium dye in tetrahydrofuran (THF) solution and in poly(methyl methacrylate) (PMMA) coating films were measured using the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of the croconium dye were obtained with a time resolution of 0.3 ps (FWHM), and were found to consist of at least two components, i.e., the coherent instantaneous nonlinear response (electronic response) and the slow response due to the formation of excited molecules for both the THF solution and PMMA coating films. The electronic component of molecular hyperpolarizability, γe, of the croconium dye in the THF solution was determined to be ca. 4.6×10-29 esu at 817 nm. The electronic component of third-order nonlinear optical susceptibility, χ(3)e, of one of the present PMMA coating films containing the croconium dye was ca. 1.3×10-8 esu at 824 nm.

Thermal and X-Ray Diffraction Studies of Liquid Crystals Incorporating a Perfluoroalkyl Group

Abstract Thermal properties of some liquid crystals incorporating a perfluoroalkyl group have been examined. The perfluoroalkyl group tends to enhance the smectic properties. The layer spacing in the smectic A and C phases was examined by X-ray diffraction, showing that the ratio of the layer spacing to the calculated molecular length is dependent on the entirety of molecular structures rather than the length of the perfluoroalkyl chain, and is in the range between 1.0 and 1.4. Novel perfluoroalkyl 3- or 4-substituted benzenes exhibiting smectic A phase were also prepared.