Azo-pendant polyamides which have the potential to photoalign chromonic lyotropic liquid crystals

A new series of polyamides (ph-azo-PAMs) was synthesized by the polycondensation of isophthalic acids having a photoisomerizable phenyl azo unit with 4,4′-diamino-3,5,3′,5′-tetraethyldiphenylmethane or by the esterification of poly(imino-5-oxyisophthaloylimino-1,4-(3,5-diethyl)phenylenemethylene-1,4-(3,5-diethyl)phenylene) with 4-(phenylazo)- or 4-(4′-substituted phenylazo)phenoxyalkanoic acid chlorides in the presence of triphenyl phosphate and pyridine in N-methylpyrrolidone. It has been confirmed that the spin-coated films of ph-azo-PAMs thus produced show reversible trans–cis photoisomerization of the azobenzene moieties. To examine the ability of the polymer films to act as command surfaces for a chromonic lyotropic liquid crystal (LLC), they were exposed to linearly polarized light and coated with aqueous LLC solutions of a chromonic dye compound. After drying the LLC solution, polarizing microscopic measurements were carried out to see whether the phototreated polymer films could bring about the in-plane anisotropic alignment of the dye molecule. The result was that 5h having an azo moiety with a dimethylamino substituent as a side group was among the most promising candidates.