Langmuir-Blodgett-Kuhn Multilayers of Polyglutamates with Azobenzene Moieties: Investigations of Photoinduced Changes in the Optical Properties and Structure of the Films

Abstract

Langmuir-Blodgett-Kuhn (LBK) multilayer assemblies of hairy-rod polyglutamates with stiff main chains and flexible side chains containing photochromic azo units exhibit a highly optically anisotropic structure when the azo molecules are in the trans form and a nearly optically isotropic structure when the azo molecules are in the cis form. The trans ↔ cis photoisomerization of the azo molecules switches them between a highly oriented trans configuration and a bend cis configuration, thus turning the anisotropy on and off' ; the corresponding optical order parameter changes by about 1 order of magnitude. In contrast to spun-cast polymer films containing azobenzene units, photoselection under polarized light irradiation does not occur in these LBK structures. The study of the electronic density distribution of these films shows that a remarkable variation in the LBK structures' stability comes with a seemingly small change in the side-chain structure. A stable LBK double-layer structure has been prepared, and its physical origin has been discussed.