Photoinduced reorientation of azo-dyes covalently linked to a styrene copolymer in bulk state

Polarized light-induced orientation in azo-dyes covalently bonded to styren e copolymer (Azo-PSCMS) was investigated by using polarized UV-VIS spectros copy. It was found that thermal isomerization and photoisomerization was sl ower and a photoinduced dichroism was larger than azo-dyes doped in polysty rene. The covalent linkage to a polymer chain may suppress both the mobilit y required for the isomerization and the rotational diffusion of the azo-mo iety. The trans --> cis photoisomerization was induced by ultraviolet (UV) light, whereas light with visible wavelength was used to drive the trans <- ---> cis photoisomerization. A high repetition of "trans-cis-trans" isomeri zation cycles achieved under visible light plays an important role for the photoinduced reorientation. Therefore, the high repetition of the "trans-ci s-trans" cycle and suppression of the rotational diffusion by the covalent linkage to a polymer are the two important factors for the photoinduced reo rientation of azo-dyes in bulk polymer matrix. (C) 2001 Elsevier Science B. V. All rights reserved.