Photoinduced orientation of azobenzene chromophores in amorphous polymers as studied by real-time visible and FTIR spectroscopies

In situ dynamical study of the photoinduced orientation of the DR1 azobenzene derivative in a doped PMMA matrix and in p(DR1A-co-MMA) copolymers was carried out using real-time visible and infrared spectroscopies. The different mechanisms occurring during the photoisomerization cycles were highlighted by following the time dependence of the normalized average absorbance (T-0), the normalized linear dichroism (T-2) and the order parameter (P-2) during the orientation (laser on) and the relaxation (laser off) periods. The thermal cis-trans back-relaxation and the angular redistribution were followed separately from the T-0 and T-2 relaxation curves, respectively. The orientation and relaxation curves were fitted by the Kohlrausch-Williams-Watts (KWW) function in order to compare the rate constant and the distribution width for various samples. On one hand, the chromophore-matrix interactions were investigated in doped systems by changing the tacticity of the PMMA matrix. On the other hand, the chromophore-chromophore interactions in functionalized polymers were studied by changing the concentration of azobenzene units in copolymer systems.