Intrazeolitic photoinduced redox reactions between tris(2,2'-bipyridine)ruthenium(2+) and methylviologen

Abstract

This study examines the photoinduced redox reactions between Ru(bpy){sub 3}{sup 2+} and methylviologen in the supercages of hydrated zeolite Y. The size of the Ru(bpy){sub 3}{sup 2+} molecules ensures that it is trapped within the supercages, yet it can interact with molecules in the neighboring cages through the 7-{angstrom} ring openings. Methylviologen, on the other hand, can migrate through the zeolite network. Evidence for photoelectron transfer from entrapped Ru(bpy){sub 3}{sup 2+} to methylviologen in neighboring cages is provided by time-resolved resonance Raman spectroscopy. Two pathways are observed for the fate of the transferred electron. Rapid back electron transfer from MV{sup {sm_bullet}+} to Ru(bpy){sub 3}{sup 3+} is observed via a second-order process on the microsecond time scale. A slower process, that occurs on a longer time scale and is observed by steady-state photolysis, leads to charge separation and stabilization of the redox pairs for extended periods. The authors have proposed that as the MV{sup 2+} diffuse through the cages, particular orientations of the molecules are established which lead to electron hopping along adjacent molecules leading to charge separation. The kinetics of this process is also influenced by diffusion of the cocation, necessary to balance the charge as the photoelectron migrates. 28more » refs., 10 figs.« less