Effect of viscosity on the rate of photosensitization of diaryliodonium salts by anthracene

We have examined the effects of viscosity on the rate of photosensitization of diaryliodonium salts by anthracene. Fluorescence spectroscopy was used to monitor the photosensitization reaction in propanol/glycerol solutions of differing viscosities. As the viscosity was increased, the rate of photosensitization decreased in a manner qualitatively described by the Smoluchowski-Stokes-Einstein equation for bimolecular elementary reactions, coupled with numerical solution of the photophysical equations. Based on these studies, we would expect the viscosity change during polymerization to have a profound effect on the rate of photosensitization due to a marked decrease in the rates of the diffusion-controlled bimolecular reactions. Therefore, the rate of photosensitization may become extremely low after a certain degree of polymerization with further reaction arising primarily from propagation of existing active centers.