Photochemical and Photoorientational Behavior of Liquid Crystalline Carbosilane Dendrimer with Azobenzene Terminal Groups

Abstract

The photochemical and photooptical properties of the first-generation LC dendrimer with terminal azobenzene groups which forms a SmA mesophase in a wide temperature range have been studied. A comparative analysis of its photochemical behavior in a dilute solution and a thin film was carried out. Under the action of UV irradiation, the E/Z photoisomerization of the azobenzene group takes place both in the solution and in the film. This process is found to be photochemically and thermally reversible. The kinetics of the thermal Z/E process is studied, and the activation energy of the process is calculated. The process of the photoinduced orientation of the terminal azobenzene groups in films of the dendrimer upon irradiation with linearly polarized UV light (365 nm) and with the green light of an Ar+ laser (488 nm) was studied. Under irradiation with linearly polarized UV light, the E/Z isomerization takes place, but photoorientation is not observed. However, in the case of linearly polarized green light exposure (488 nm), a well pronounced linear dichroism is generated. The kinetics of the process was studied, and the photoinduced orientational order parameter was calculated.