Electron transfer in a poly(ethylene oxide) (PEO) film has been investigated by the quenching of photoexcited Ru(bpy)(3)(2+) by 10-methylphenothiazine (MPTZ) and/or methylviologen (MV2+) dispersed in the film. Photoinduced electron transfer occurs by both the dynamic and static mechanisms. The electron transfer rate constants and characteristic electron transfer distances were 4.6 x 10(6) M-1 s(-1)/1.2 nm from MPTZ to Ru(bpy)(3)(2+)* and 1.3 x 10(7) M-1 s(-1)/1.7 nm from Ru(bpy)(3)(2+)* to MV2+ in each system. The diffusion coefficient of the molecules was estimated from the electron transfer rate constant and the electron transfer distance to be the order of 10(-8)-10(-9) cm(2) s(-1).