Journal of Physical Chemistry, Vol.99, No.16, 6152-6162, 1995
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), Ru(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, respectively, with organic quenchers were investigated in acetonitrile solutions, and their Delta G dependencies of the quenching rate constants (k(q)) were compared with those of Ru(bpy)(3)(2+) (bpy = 2,2’-bipyridine) 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). The 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 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)(3)(2+) and Ru(azpy)(3)(2+) coincide with that of the corresponding bpy complex. The inner-sphere reorganization (lambda(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)(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 are discussed and compared with other donor-acceptor systems.
Keywords:EXCITED-STATE;RUTHENIUM(II) COMPLEXES;POLYPYRIDINE COMPLEXES;METAL-COMPLEXES;AROMATIC-AMINES;LARGE MOLECULES;FREE-ENERGY;LUMINESCENCE;2-(PHENYLAZO)PYRIDINE;PHOTOCHEMISTRY