Photoinduced control over the self-organized orientation of amorphous molecular materials using polarized light

Novel chiral amorphous molecular materials containing photoresponsive azobenzene moieties were designed and synthesized. These materials led to the formation of smooth and uniform thin films without grain boundaries. Photoirradiation of the thin film with linearly and elliptically polarized light caused trans-cis photoisomerization of the azobenzene moieties and resulted in an anisotropic orientation of the materials. Maximum change in a value of birefringence, Deltan, after irradiation of the linearly polarized light is about 0.08 with a response time of 10 s. However, when irradiation was ceased after photoinduced orientation, the value of Deltan decreased due to relaxation of the azobenzene moieties. Furthermore, these materials exhibited a high efficiency of a photoinduced polarization rotation over 30 deg mum(-1) after irradiation with the elliptically polarized light for 60 s. We also found that the efficiency depends on ellipticity of the incident light and on the thickness of the sample. The origin of the large change in the molecular orientation is the anisotropic arrangement of the azobenzenes in the terminal groups upon irradiation with the linearly and elliptically polarized light.