Zbigniew Galewski

Ferroelectric phase transition in [(CH3)3 NH]3 Sb2Cl9 (TMACA)

Abstract The ferroelectric first order phase transition at 367 K has been discovered in TMACA crystals, which is presumably related to a motion of trimethylammonium cations.

Liquid crystalline properties and phase situations in 4-chlorobenzylidene-4′-alkylanilines

Abstract On the basis of DSC calorimetry and thermo-optic (TOA) measurements the mesomorphic properties of the strongly polar Schiff bases family, 4-chlorobenzylidene-4′-alkylanilines (CBnA), are presented. Two kinds of mesophases were found: smectic A and smectic B. For the first time detailed calorimetric properties of the investigated family are presented and discussed. Very narrow smectic A phase for the nonyl, decyl, undecyl and dodecyl derivatives was detected. Smectic mesophases in butyl, pentyl and dodecyl derivatives are monotropic. These results are compared with our earlier results [1].

The kinetics of the E-Z-E isomerisation and liquid-crystalline properties of selected azobenzene derivatives investigated by the prism of the ester group inversion

Two new groups of azobenzene ester derivatives were synthesised: alkyl 4-[4-(nonyloxy)phenyl]diazenyl]benzoates and 4-[4-(nonyloxy)phenyl]diazenyl]phenyl alkanoates. All 35 presented homologues are mesogenic. Moreover, some of the above-mentioned compounds exhibit rich liquid-crystalline polymorphism likewise tetramorphism. During this investigation by the use of polarising optical microscopy, differential scanning calorimetry and X-Ray studies, six types of mesophases were detected: nematic, smectics (A, C, I, F) and G. Furthermore, due to the presence of the photosensitive azo moiety, the E–Z isomerisation reaction is possible. This process, which is initiated by the UV irradiation, causes significant changes in the UV-Vis absorption spectra of investigated compounds. However, the photoisomerisation is a reversible process and in the dark the thermal relaxation of Z isomer takes place. Based on the achieved data, the kinetic constants of the isomerisation and relaxation processes were calculated. It shows that conversion of the ester bond makes some changes in the optical properties. The shift of about 7 nm of the absorbance maximum was observed. Surprisingly, the inversion of the ester group has significant influence on the liquid-crystalline polymorphism replacing one mesophase (for benzoates) into four (for alkanoates).

Smectic polymorphism of 4-decyloxybenzylidene- 4′-alkyloxyanilines and their mixtures with polar standards of mesophases

This article describes liquid crystalline properties of the homologous series of 4-decyloxybenzylidene-4′-alkyloxyanilines. Based on the polarization microscopy (POM and TOA methods) and the calorimetric (DSC) measurements a rich polymorphism has been detected. Investigated compounds exhibit nematic, smectic A, smectic C, smectic B, smectic I and G (smectic G) mesophases with their characteristic configurations. The presence of these mesophases was confirmed by the miscibility method, using 4-heptyloxybenxylidene-4′-pentylaniline as a mesophase reference. Nine other smectic standards with different polarity have been applied in order to investigate their influence on the mesophase stability.

Smectic polymorphism of the 4-butyl-4-alkoxyazobenzenes and 4-pentyl-4-alkoxyazobenzenes

Two families of liquid crystalline compounds have been synthesised, the 4-butyl-4- alkoxyazobenzenes and the 4-pentyl-4-alkoxyazobenzenes; for the second family results are presented for the first time for alkoxy chains longer than butyl. The results for both families have been obtained up to the octadecyl homologues. In both families, on the basis of DSC, polarizing microscopy and thermo-optical analysis, a rich polymorphism has been detected (maximum tetramorphism). The smectic properties start with the hexyl derivative (for the butyl family) and with the heptyl derivative (for the pentyl family). Strong odd-even effects for the temperatures of clearing in both groups of compounds were detected. Our results are compared with those of de Jeu et al. and of Adomenas et al. for the 4-butyl-4- alkoxyazobenzenes, for which only one smectic modification was described.

Liquid Crystalline Properties of 4-Alkoxy-Aniline-4′-Alkoxy-Anilines

Abstract Liquid crystalline properties of the four families with the general formula: where X = NO2, Cl, Br, F, have been investigated. Among these compounds nematic, smectic A and smectic B mesophases were found. These phase situations are compared with the isomeric families with the reversed -N=CH- central group.

Kinetics of Photochromic Reactions of Substituted Azobenzenes in Solutions, and in Liquid Crystalline and Polymer Matrices

Abstract Kinetics of photochromic reactions was studied in azobenzene derivatives: azobenzene-containing crown ethers, and 4-methoxy-4′-halogen-substituted azobenzenes capable of forming liquid crystalline phases. The photoactive materials were dissolved in alkanes, and in polymer and liquid-crystalline matrices. The isomerisation reactions follow the first order kinetics, in some polymer matrices, however, a dispersion of the rate constants was found. Thermal cis-trans isomerisation rates of halogen-substituted azobenzenes in n-heptane were found practically independent of the substitutent. Kinetics of the same reactions in liquid crystalline matrices seems to exhibit anomalies near phase transitions of the matrices.

Influence of terminal groups on liquid-crystalline polymorphism of selected azobenzene derivatives

This article describes the synthesis and liquid-crystalline characterisation of four kinds of azobenzene derivatives: 1-[4-(hexyloxy)phenyl]-2-(4-X-phenyl)diazenes (A), 4-[(4-X-phenyl)diazenyl]phenyl heptanoates (B), 4-[(4-X-phenyl)diazenyl]phenyl 4-(dodecyloxy)benzoates (C) and 4-[(4-X-phenyl)diazenyl]phenyl 4-{[(2S)-2-chloropropanoyl]oxy}benzoates (D), where X is the alkyl, alkyloxy alkylcarbonyl and alkyloxycarbonyl substituents. Among the 32 calamitic mesogens presented (13 of them are described here for the first time), the following mesophases were observed: nematic, SmA, SmC, Bhex, BCr and G. About half of the investigated compounds exhibit more than one mesophase. We noted and compared the relationship between the type of the substituent and the type of liquid-crystalline phases and their temperature ranges.

Liquid crystalline properties of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines

The liquid‐crystalline polymorphism of the homologous series of 4‐hexyloxybenzylidene‐4′‐alkyloxyanilines is investigated. Basing on the polarization microscopy (POM, TOA), the DSC calorimetry and miscibility studies the following mesophases were detected: nematic, smectic A, smectic C and smectic I. The phase diagrams of the compounds of these series with 4‐hexyloxybenylidene‐4′‐pentylaniline (as the standard of mesophases) show induction of the smectic F mesophases. Their dependence on the alkyl chain length and mole fraction is shown. *. Present address: Department of Chemistry, University of Pennsylvania, 231 South 34th St., Philadelphia, PA 19104, USA

Smectic polymorphism of 4-dodecyloxybenzylidene-4′-alkyloxyanilines

Liquid crystalline properties of the homologous series of 4-dodecyloxybenzylidene-4′-alkyloxyanilines are described. Nematic, smectic A, smectic C, smectic B and smectic I mesophases were detected. The influence of an alkyl chain length on the mesophase sequence and the entropic effects are broadly discussed. The unexpected change of the orthogonal smectic B mesophase into the tilted smectic I mesophase was observed for derivatives with longer than hexyl (n = 6) chains. The identification of mesophases by polarization microscopy and miscibility method is discussed. The influence of the alkyl chain length on the topology of the mesophase diagrams for mixtures of investigated compounds with 4-heptyloxybenzylidene-4′-pentylaniline and 4-nonyl-4′-decyloxyazobenzene used as the standards of smectic mesophases is demonstrated.