Photoassisted poling and orientational relaxation of dye molecules in polymers: the case of spiropyran

Photoassisted poling of azo-dyes in polymer films is now well-known: it is a consequence of trans-cis photoisomerization. We report new experiments involving the photoisomerization of spiropyrans into merocyanines. With the help of a theoretical model, we discuss poling mechanisms. The study of the relaxation of electro-optical properties of photomerocyanine gives new results on the rotational mobility of dye molecules in polymers: in addition to the site-to-site variation, it is necessary to introduce a time variation of the mobility, after the end of the poling process.