OXIDATIVE PHOTOBLEACHING OF SUBSTITUTED ANTHRACENES IN THIN POLYMER-FILMS

The photochemical reaction of diphenylanthracene (DPA) and dimethylanthracene (DMA) in thin spin-cast films of various polymers in the presence of oxygen, with direct irradiation as well as triplet sensitization, is reported. Kinetic equations are derived and used in conjunction with the analytical results of Sheats, Diamond, and Smith to determine reaction parameters from the optical transmittance data. Triplet yields are about 40%. The oxidation rates are substantially lower than in solution, more so for DMA than for DPA. The rate for DPA in poly(ethyl methacrylate) (PEMA) is similar to that in poly(diphenylsiloxane) (PDPS), while in poly(butyl methacrylate) (PBMA) it is significantly faster. The absorption spectra are not concentration dependent up to 40 wt %, although some changes are observed in emission. The kinetic analysis demonstrates that in some cases (but not in others) the rate law has a component not present in fluid solution; this is interpreted to be related to the effect of polymer microviscosity, which changes during the reaction. The nature of the effect in the present system is different from the behavior of other polymer photoreactions such as azobenzene or spiropyran isomerizations. © 1990 American Chemical Society.