Z-Isomers of 3,3′-disubstituted azobenzenes highly compatible with liquid crystals

Abstract

It is known that mesophase changes can be induced by E-Z photoisomerization of azobenzenes doped in liquid crystals. Novel azobenzenes have been designed on the basis of Molecular Mechanics and Molecular Orbital calculation, aimed at exploiting novel photoresponsive guest-host liquid crystalline systems exhibiting no mesophase change despite the drastic structural alteration of the guest molecules. It was found that the introduction of alkanoyloxy groups at both the 3- and 3′-positions of azobenzene leads to phase stability of nematic systems upon the E-Z photoisomerization even at a dopant concentration as high as 20 wt%. However phase separation was brought about when 3,3′-dialkoxyazobenzenes and 4,4′-dialkoxyazobenzenes were employed as guest molecules. The relation between the conformational structures of the guests in their E- and Z-isomers and their compatibility with nematic hosts was examined thermodynamically. Experimental results were compared in some details with the simulations. It was shown that 3,3′-dialkanoyloxyazobenzene prefers a rod-like structure in both E- and Z-isomers.