Mesomorphic properties of diesters with p-substituted-arylazomethine pendant groups

SANDRA A. HERNÀNDEZ; RAÚL O. GARAY

MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY, SECTION A

Taylor & Francis Group Ltd

Lugar: London, UK; Año: 2006 vol. 451 p. 21 - 32

1058-725X

The substituent steric and electronic effects on mesophase stability and glass-forming properties of a series of 1,4-bis-(4-n-alkyloxybenzoyloxy)-2-N-(p-Y-aryl)azomethinebenzenes were evaluated. The diesters showed a typical though mild dependence of the monotropic nematic-isotropic transition temperatures on the substituent size that was attributed to the conformational flexibility of the pendant azomethine group. In contrast, the dependence of the entropy change associated with the nematic-isotropic transition showed an atypical behavior ascribed to the extreme reduction of the mesogen axial ratio. The introduction of the bulky arylazomethine group on a lateral position originated significant crystallization supercooling. The appearance of glassy mesophases was detected in some of the diesters, the OEt and CF3 groups being the more effective substituents to promote the formation of nematic glasses.