TOWARD THE DEVELOPMENT OF SUPRAMOLECULAR METAL-COMPLEX LIGHT-HARVESTING ARRAYS - FACTORS AFFECTING PHOTOINDUCED ENERGY-TRANSFER IN BIMETALLIC COMPLEXES

A series of bimetallic noble metal complexes were prepared which have luminescent metal-to-ligand charge transfer excited states associated with both metal centers. Electronic interaction through the bridging l igand, s[2-(4'-methyl-2,2'-bipyridyl-4-yl)-ethyl]benzene, is weak enou gh that the redox and spectroscopic properties of the individual metal centers of the complexes are unperturbed. Exchange energy transfer oc curs from the metal center with the higher energy MLCT state to the ot her center in each unsymmetric bimetallic complex. The energy gap depe ndence for the series shows an increase in the observed rate constant with increasing Delta E. The process was assumed to be nonadiabatic an d the data were fit using a Golden Rule formalism. Fitting parameters were obtained from Franck-Condon analysis of emission spectral profile s of the donor and acceptor chromophores. Results indicate that reorga nizational energies calculated from spectral fitting procedures undere stimate the magnitude of the barrier associated with the intramolecula r energy transfer process.