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

Photoinduced oxidative and reductive electron transfer (ET) reactions of excited Ru(imin)(3)(2+) (imin = 2-(N-methylformimidoyl)pyridine), R u(imin)(2)(CN)(2), and Ru(azpy)(3)(2+) (azpy = 2-(phenylazo)pyridine), where imin and azpy contain imine C=N and azo N=N double bonds, respe ctively, with organic quenchers were investigated in acetonitrile solu tions, and their Delta G dependencies of the quenching rate constants (k(q)) were compared with those of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridi ne) and Ru(L)(2)(CN)(2) complexes where L = 4,4'- or 5,5'-dmbpy (dmbpy = dimethyl-2,2'-bipyridine) and phen (phen = 1,10-phenanthroline). Th e oxidative quenching rate constants of Ru(imin)(3)(2+) and Ru(imin)(2 )(CN)(2) are smaller than those of the corresponding bpy, dmbpy, and p hen 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)(3)(2+) and Ru(azpy)(3)(2+) coincide with that of the corresp onding bpy complex. The inner-sphere reorganization (lambda(in)) cause d by the deformation of the C=N bond of imin is considered to be the m ain reason for the disadvantage of ET in the normal region of the oxid ative ET reactions of excited Ru(imin)(3)(2+) and Ru(imin)(2)(CN)(2). On the other hand, the deformation of the C=N and N=N bonds of Ru(imin )(3)(2+) and Ru(azpy)(3)(2+) is absent in the reductive ET reactions. The factors which govern these oxidative and reductive ET reactions ar e discussed and compared with other donor-acceptor systems.