Synthesis and Study of New Mesogens II: p-(p′-n-Alkoxycinnamoyloxy)-benzylidene p″ -anisidines (1) and p-(p′-n-Alkoxycinnamoyloxy)- benzylidene anilines (2)

Abstract

Two new homologous series of liquid crystals viz. p-(p'-n-alkoxycinnamoyloxy) benzylidene p”-anisidines (1) and p-(p'-n-alkoxycinnamoyloxy) benzylidene anilines (2) comprising twenty four mesogens have been synthesized. Both are high melting series of mesomorphs. In the homologous series (1) the nematic mesophase is exhibited from the very first member; however, the first five compounds decompose at high temperatures before passing into isotropic liquid condition. Polymesomorphism is exhibited with the appearance of the smectic mesophase at the octyl derivative and remains up to the last viz. octadecyl homologue. Within polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown i. e. in the first seven members of the homologous series (1). The smectic mesophase shows focal conic fan shape texture belonging to smectic-A variety. The nematic-isotropic curve shows descending tendency as the series is ascended-a characteristic of high melting series. The smectic-nematic transition curve rises steeply and shows a levelling off tendency at the octadecyl derivative. In the homologous series (2), no decomposition occurs. The smectic mesophase commences a little early i. e. from hexyl derivative; while polymesomorphism is clearly exhibited up to the dodecyl derivative, the last two homologues are purely smectogens. The usual odd-even effect is observed in case of the nematic-isotropic curve for series (2). The smetic-nematic curve rises gradually and seems to be merging with the falling nematic-isotropic curve at the fifteenth homologue. The mesomorphic ranges in both series are quite wide; however, that of series (1) is wider than one obtained in series (2). Thermal stabilities are good and are in keeping with the molecular characteristics. The textures of the smectic and nematic mesophases are similar to that of the series (1). Both series are comparable with each other and other related series.