Electron paramagnetic resonance and electron nuclear double resonance studies of photoinduced charge separation from N-methylphenothiazine doped into poly(ethylene oxide) and poly(propylene oxide) polymer matrices

Abstract

Photoionization of N-methylphenothiazine (PC₁) doped into poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) matrices results in paramagnetic cation radical formation. The radicals were identified by electron paramagnetic resonance from the g-factor and hyperfine splitting. The radical quantity was determined by double integration of the EPR spectra. The amount of cation radical produced by photoionization is greater in PEO than in PPO and the lifetime of photoproduced radicals is relatively longer in PEO than in PPO. These results are interpreted as due to a shorter electron transfer distance in PEO and to faster radical conversion from phenothiazine cation radical to polymer alkyl chain radicals. This explanation is supported by larger proton matrix electron nuclear double resonance linewidths in PEO than in PPO. Also, the relaxation kinetics of the photoinduced charge separated state in the polymer matrices was studied and fitted to a biexponential equation.