Rapid Decoloration of Photochromic 3H-Naphthopyran Attached to Three-Dimensional Poly(dimethylsiloxane) Network

The attachment of 3H-naphthopyran to a three-dimensional network of polysiloxane elastomer was carried out by hydrosilylation reactions using 3H-9-(5-hexenyloxy)naphthopyran. The photochemical coloration and subsequent thermal decoloration behaviors of polysiloxane-bound 3H-naphthopyran molecules were examined by comparing their properties with those of a model 9-hexyloxy-3H-naphthopyran compound doped in a polysiloxane film, a PMMA film, and in solutions. The decoloration reaction rate of polysiloxane-bound naphthopyran was basically the same as that in the polysiloxane-doped system and in solutions. However, the polysiloxane-bound system is superior to the doped system due to: (1) more concentrated incorporation of naphthopyran molecules in the polysiloxane film; (2) less degradation of naphthopyran molecules during film preparation; and (3) less temperature dependence in the thermal decoloration rate.