REDUCTIVE QUENCHING OF THE EXCITED-STATES OF RUTHENIUM(II) COMPLEXES CONTAINING 2,2'-BIPYRIDINE, 2,2'-BIPYRAZINE, AND 2,2'-BIPYRIMIDINE LIGANDS

The reductive quenching of the luminescent excited states of Ru(II) complexes of the general formula Ru(bpy)(3-m-z)(bpm)(m)(bpz)(z)(2+) (bpy = 2,2'-bipyridine, bpm = 2,2'-bipyrimidine, bpz = 2,2'-bipyrazine, m and z = 0,1,2,3 and m + z less than or equal to 3) by aromatic amines and methoxybenzenes as nonsacrificial electron donors and by C2O42-, EDTA, and TEOA as sacrificial donors in aqueous, acetonitrile, and propylene carbonate solution was examined by continuous and pulsed laser flash photolysis techniques. From k(q), a value of E degrees for the irreversible oxidation of TEOA (-0.84 +/- 0.12 V vs NHE) in acetonitrile was obtained. Values of the cage escape yield of redox products (eta(ce)) showed weak or no dependencies on the driving forces of back electron transfer within the geminate redox pair in the solvent cage (Delta G(bt)degrees), suggesting that the simple model of competition between cage escape and back electron transfer may be inadequate to describe the results. A modification of the simple model, in which is introduced a kinetically important reorientation of the geminate redox pair, is proposed.