Photo-reorientation of azobenzene side groups of thermotropic ‘hairy rod’ polyglutamate in LB multilayers

Abstract

A polyglutamate with photochromic azobenzene side groups combines thermotropic properties with the capability to form Langmuir-Blodgett (LB) multilayers. On irradiation with linearly polarised light the azobenzene side groups may be reoriented in spin-coated films and LB multilayers perpendicular to the electric field vector of the incident light. But the photochemically induced reorientation process depends strongly on the supramolecular order and on the irradiation conditions. Thus, the stable nematic-like order of the ‘hairy rod’ backbones restricts the photo-reorientation process of the azobenzene side groups within the LB multilayer, in contrast to the spin-coated film. In this case the degree of the photo-induced anisotropy depends on the primary orientational order of the multilayer, the molecular aggregation of the azobenzene moieties and on the conditions of light exposure. The photo-reorientation process becomes more efficient after weakening the intermolecular interactions by a suitable preparation of the films or by an intermediate photochemical decoupling of the supramolecular order caused by an ultraviolet irradiation step.