EFFECT OF LASER INTENSITY ON THE DETERMINATION OF INTERMOLECULAR ELECTRON-TRANSFER RATE CONSTANTS - OBSERVATION OF MARCUS INVERTED REGION IN PHOTOINDUCED BACK ELECTRON-TRANSFER REACTIONS

The light intensity and concentration dependence of the photoproduct y ield are investigated in a monophotonic process, The relationship of t he photoproduct yield with the laser intensity and the complex concent ration for a monophotonic process is derived under laser flash photoly sis. The relationship is confirmed experimentally in a monophotonic pr ocess, i.e., triplet-triplet transition for a Cu(I) complex Cu-6(DMNSN ')(6) (DMNSN' = 4,6-dimethylpyrimidine-2-thiolate). At low light inten sity, the relationship can be approximated by a linear inverse square root dependence on the light intensity. Based on this equation, a meth od is proposed to determine the intrinsic back electron transfer rate constant kb,in photoinduced intermolecular electron transfer reactions , precluding the effect from the diffusional encounter pairs. The Marc us ''inverted region'' is observed by using the method in photoinduced back electron transfer reactions of [Au-2(dppm)(2)](ClO4)(2) (dppm = bis(diphenylphiosphino)methane) with a series of substituted pyridiniu m acceptors. (C) 1998 American Institute of Physics.