The influence of intramolecular hydrogen bonding on the order parameter and photostability properties of dichroic azo dyes in a nematic liquid crystal host

It has been demonstrated that intramolecular hydrogen bonding in two classe s of dichroic azo dyes has a generally detrimental effect on order paramete r in a nematic liquid crystal host. Derivatives of 4-(N,N-diethylamino)-4'- nitroazobenzene with hydroxy groups intramolecularly hydrogen bonded to the azo group show lower order parameters in E7 nematic liquid crystal than th e parent dye, but higher order parameters than corresponding methoxy dyes. 1-Arylazo-2-naphthols with a hydrogen bonding carboxamide group in position 3 exist exclusively in the hydrazone form and show even lower order parame ters. Intramolecular hydrogen bonding also has a deleterious effect on phot ochemical stability.