Rate dependence of electron transfer on donor-acceptor separation and on free enthalpy change. The tris(2,2'-bipyridine)ruthenium(2+)/viologen2+system

Publikations-Art

Zeitschriftenbeitrag

Autoren

Rau, H.; Frank, F.; Greiner, G.

Erscheinungsjahr

1986

Veröffentlicht in

J. Phys. Chem.

Band/Volume

90/11

Seite (von - bis)

2476-81

By attachment of hydrocarbon chains of different lengths to the bipyridyl ligands in Ru(bpy)32+ the donor-acceptor sepn. was adjusted in the electron-transfer system Ru[(CnH2n+1)2bpy]32+/methylviologen. Two electron-transfer reactions with different .DELTA.G were investigated in fluid soln.: the quenching of the excited complexes by methylviologen (MV2+) is exothermic by -0.4 eV and the thermal back electron transfer is exothermic by -1.7 eV. An exponential decrease of the quenching rate on distance was obsd. The back electron transfer is independent of donor-acceptor sepn.; electron transfer takes place at distances of .gtoreq.1.5 nm. The results are discussed in terms of a hypothesis on the interdependence of transfer distance and free enthalpy change and compared with current theories. In the framework of the simple classical Marcus model, the Marcus equation relating transfer rate and free enthalpy change is transposed into the Rehm-Weller equation by simple math. manipulations and the implications of this are discussed.