Reactions of ferrocenes and ferrocenium ions with ground and excited states of tris(2,2'-bipyridine)chromium ions

The kinetics of quenching of *Cr(bpy){sub 3}{sup 3+} by d{sup 6} metallocenes and by ferrocenium ions were evaluated by laser flash photolysis. The quenching by ferrocenium ions proceeds by energy transfer and is dependent on the donor-acceptor distance, as expected for an electron-exchange mechanism. The rate constants for quenching with d{sup 6} metallocenes are at or near the diffusion-controlled limit. The reactions partition themselves between electron transfer and energy transfer. The Cr(bpy){sub 3}{sup 2+} and the ferrocenium ions, formed by electron-transfer quenching, undergo rapid back electron transfer, k = (3-9) {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1}. 28 refs., 2 figs., 3 tabs.