Yields of Electron Transfer Reactions in the Quenching of the Phosphorescent States (2E) of Tris(2,2′-bipyridine)chromium(III) and Tris(4,7-diphenyl-1,10-phenanthroline)chromium(III) Compounds

Molar absorption coefficients of the phosphorescent states (2E) of [Cr(2,2′-bipyridine)3]3+ and [Cr(4,7-diphenyl-1,10-phenanthroline)3]3+ were determined. The 2E state of [Cr(2,2′-bipyridine)3]3+ was reduced to [Cr(2,2′-bipyridine)3]2+ with the yield of less than 0.2 in the quenching by iron(II) compounds. The reduction yields of [Cr(2,2′-bipyridine)3]3+ and [Cr(4,7-diphenyl-1,10-phenanthroline)3]3+ in the quenching of 2E by aromatic amines increase with the Gibbs energy change (−ΔG) in the reverse electron-transfer process. The weak dependence of the yields on ΔG can not be interpreted in terms of adiabatic reverse electron transfer in the geminate pair, which is formed in the quenching process. The electron transfer from the chromium(II) compounds of triplet spin-multiplicity to the amine radical of doublet spin-multiplicity suffers from spin-restriction.