Retardation of the orientation relaxation of azo-dye doped amorphous polymers upon photoinduced isomerization

Abstract

The orientation relaxation upon photo-induced isomerization of azo-dyes was studied. All-optical poling (AOP) and photo-induced birefringence, which are based on the mechanism of angular selective photo-isomerization, were employed to manipulate the angular distribution of azo-dyes (Disperse-red 1) doped in three different amorphous polymers: (poly(methyl methacrylate) PMMA, poly(carbonate) PC and poly(sulfone) PSU), with different glass transition temperature (Tg). In the case of AOP, quasi-permanent macroscopic second-order nonlinear optical susceptibility χ(2) was inscribed in the dye-doped centro-symmetric polymer systems, while in the case of photo-induced birefringence, quasi-permanent birefringence Δn was inscribed in the dye-doped isotropic polymer systems. Relaxation of χ(2) and Δn were monitored upon different duration of AOP and photo-induced birefringence preparation. Experimental results show that azo-dye orientation relaxation follows the duration of the photo-nduced isomerization process: the longer the photo-induced isomerization process, the slower the relaxation of the inscribed χ(2) and Δn. In addition, retardation of the orientation relaxation does not follow a simple relation with hardness (Tg) of the polymer host. Causes of the orientation relaxation retardation are discussed.