Polarity and steric effect of di-lateral substitution on the mesophase behaviour of some azo/ester compounds. Issue 11 (2nd September 2017)

• Record Type: Journal Article
• Authors: Naoum, Magdi M.; Fahmi, Abdelgawad A.; Saad, Gamal R.; Ali, Mohamed H.
• Is Part Of: Liquid crystals. Volume 44:Issue 11(2017)
• Page Start: 1664
• Page End: 1677
• Publication Date: 2017-09-02
• Subjects: di-lateral substitution -- azo/ester compounds -- phase behaviour -- dipole moment -- optical property; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2017.1306886
• Languages: English
• ISSNs: 0267-8292

Abstract

ABSTRACT: Eight homologous series of 2-(or 3-)substituted phenyl 4ʹ-(4″-alkoxy (2ʹ-, or 3″-substituted phenylazo) benzoates (I n XY ) were prepared in which the suffix 'X' refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix 'Y' refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies from 8 to 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3 and F. The mesophase behaviour was investigated by differential scanning calorimetry and identified by polarised optical microscopy. The results were discussed in terms of the polarity and steric effects of the two lateral substituents. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behaviour of the previously investigated mono-laterally substituted analogues. UV–vis spectroscopic study revealed that the compoundsI 8 XY exhibited two absorption bands: low intense bands at 254–263 and a broad band at 364–376 nm. These bands are attributed to the π–π∗ transition of the phenyl rings and the whole mesogenic portion. Graphical Abstract: