Role of the Inner-Sphere Reorganization in the Photoinduced Electron Transfer Reaction of Ru(II) Complexes Containing Imine C:N or Azo N:N Double Bonds in the Ligands

Abstract

Photoinduced oxidative and reductive electron transfer (ET) reactions of excited Ru(imin){sub 3}{sup 2+} (imin = 2-(N-methylformimidoyl)pyridine), Ru(imin){sub 2}(CN){sub 2}, and Ru(azpy){sub 3}{sup 2+} (azpy = 2-(phenylazo)pyridine), where imin and azpy contain imine C=N and azo N=N double bonds, respectively, with organic quenchers were investigated in acetonitrile solutions, and their {Delta}G dependencies of the quenching rate constants (k{sub q}) were compared with those of Ru(bpy){sub 3}{sup 2+} (bpy = 2,2`-bipyridine) and Ru(L){sub 2}(CN){sub 2} complexes where L = 4,4`- or 5,5`-dmbpy (dmbpy = dimethyl-2,2`-bipyridine) and phen (phen = 1,10-phenanthroline). The oxidative quenching rate constants of Ru(imin){sub 3}{sup 2+} and Ru(imin){sub 2}(CN){sub 2} are smaller than those of the corresponding bpy, dmbpy, and phen complexes at the same {Delta}G value in the normal region. However, the {Delta}G dependencies of the reductive quenching rate constants of Ru(imin){sub 3}{sup 2+} and Ru(azpy){sub 3}{sup 2+} coincide with that of the corresponding bpy complex. The inner-sphere reorganization ({lambda}{sub in}) caused by the deformation of the C=N bond of imin is considered to be the main reason for the disadvantage of ET in the normal region of the oxidative ET reactions of excited Ru(imin){sub 3}{sup 2+} and Ru(imin){sub 2}(CN){sub 2}. 44 refs., 6 figs., 6 tabs.