DYNAMIC ELECTRON-TRANSFER QUENCHING OF THE TRIS(2,2'-BIPYRIDYL)RUTHENIUM(II) MLCT EXCITED-STATE BY INTRAZEOLITIC METHYLVIOLOGEN IONS

Photoinduced electron-transfer reactions of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) and methylviologen (MV2+) ion-exchanged onto/into three different zeolites (L, Y, and mordenite) were studied by steady-state and time-resolved spectroscopic techniques. Quenching of the metal-to-ligand charge-transfer (MLCT) excited state of the size-excluded Ru(bpy)3(2+) ion was shown to be controlled by diffusion of MV2+ within the channels of both zeolite L and Y. Linear Stern-Volmer plots were derived from time-resolved emission and transient diffuse reflectance data for these two zeolites. Quantitative agreement with steady-state emission data showed that static quenching was not significant in these cases. In the case of mordenite, nonlinear Stern-Volmer plots were obtained. Using a modified Smoluchouski equation, the diffusion coefficients of MV2+ in zeolites L and Y were estimated as 1.28 x 10(-7) and 1.12 x 10(-7) cm2 s-1, respectively. The charge recombination kinetics of the photoproducts Ru(bpy)3(3+) and MV.+ in zeolites L and Y are complex and do not follow first- or second-order decays. The average lifetimes of charge separation were in the range of tens of microseconds. Quantum yields for charge separation and cage escape efficiencies for Ru(bpy)3(3+) and MV.+ in these zeolites were found on the order of 6-9%.