ELECTRON AND ENERGY-TRANSFER AS PROBES OF INTERPARTICLE ION-EXCHANGE REACTIONS IN ZEOLITE-Y

Photoinduced electron transfer and energy transfer reactions of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) with methylviologen (MV2+) and tris(2,2-bipyridyl)osmium(II) (Os(bpy)3(2+)) ion-exchanged onto/into separate zeolite Y particles were studied by emission spectroscopy. The kinetics of interparticle exchange were probed by observing the quenching of the MLCT excited state of Ru(bpy)3(2+) by mobile MV2+ or Os(bpy)3(2+) ions. The exchange reactions occur on time scales of seconds to hours, depending on the ionic strength of the surrounding medium. The time-dependent luminescence data were fitted to a dispersed kinetics model, from which average rate constants for the exchange reactions could be extracted. Time constants for interparticle exchange of MV2+ and Os(bpy)3(2+) ions, in the range 10(3)-10(5) S at electrolyte concentrations of 0. 1-3 mM, are significantly longer than the time scales (10(-7)-10(1) s) of most electrochemical and photochemical intrazeolitic reactions involving these and similar electroactive ions. These results argue for reaction mechanisms that invoke intrazeolite electron transfer, rather than exchange of electroactive ions followed by solution-phase electron transfer, in these systems.