Effect of exchange of terminal substituents on the mesophase behaviour of some azo/ester compounds

Abstract

Six homologous series of 4-(4′-alkoxy phenylazo) phenyl 4″-substituted benzoates (In a-f ) were prepared in which, within each homologous series, the length of the terminal alkoxy chain varies between 6, 8, 10, and 12 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH 3 O, CH 3 , H, Br, NO 2 and CN. Compounds prepared were characterised by spectroscopic methods, and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The results were discussed in terms of mesomeric and polarisability effects. In each group of compounds, bearing the same alkoxy substituent, the nematic-to-isotropic transition temperatures (T C ) were successfully correlated with the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and their previously prepared isomers, namely, 4-(4′-substituted phenylazo) phenyl 4″-alkoxybenzoates (IIn a-f ) in which the two terminal (alkoxy-and X) groups are exchanged.

The effect of inversion of the ester group on the mesophase behaviour of some azo/ester compounds

“…[30] Corresponding data for compounds IIn a-e and IIIn a-e are given elsewhere. [23,24] The synthesised compound of the present work, showed to display pronounced thermal stability, when heated. Thus, when the samples were subjected to repeated heating/cooling cycles, the DSC profiles exhibited similar behaviours.…”

“…This inference is in accordance with the experimental results (Table 1, refs. [23,24]); the cyano analogues (in series I, II and II) have the highest clearing (T C ) temperatures.…”

“…[13,14] A number of homologous series with ester and azo central linkages have been synthesised having different terminal groups. [15][16][17][18][19][20][21][22] The goal of the present work is to prepare a series of model compounds of the type 4-substituted phenyl 4ʹ-alkoxy phenylazo-4′-benzoates (In a-e ), in which the ester groups (OOC) in the previously investigated isomeric derivatives, [23] namely, 4-(4ʹ-alkoxy phenylazo) phenyl-4′-substituted benzoates (IIn a-e ), are inverted in the present investigation to COO. As expected, inversion of the ester group in a compound of type II, results in an isomer that would react mesomerically in a different way and consequently affect their mesophase behaviour differently.…”

Photoresponsive behavior of hydrophilic/hydrophobic-based novel azobenzene mesogens: synthesis, characterization and their application in optical storage devices

“…12,13 The decoration of different functional groups on the azobenzene chromophore has been studied to enhance its optical storage properties. [14][15][16][17][18][19][20][21] Ionic liquids have been developed in the past two decades because of their unique physicochemical properties and highly tunable features with chemical modication. [22][23][24][25] Thus, it is possible to design functionalized azobenzene-based ionic liquids by introducing quaternary ammonium salts into the photoresponsive unit of azobenzene.…”

Mesophase behaviour of laterally di-fluoro-substituted four-ring compounds

“…[1,2] From these structural investigations, one can mention the ester orientation within the rigid core, the position of azo/ester groups, lateral substitutions, as well as the terminal chain length. [3][4][5][6][7][8][9][10][11][12] In a liquid crystal compound, lateral substitution makes molecules broad, thus playing an effective role in the mesogenic properties of the resulting derivatives. Lateral substituent in rigid core can destroy the molecular closed packing, reduce liquid crystal melting point, thereby improving the solubility of liquid crystal effectively.…”