PHOTOINDUCED INTRAMOLECULAR ELECTRON-TRANSFER IN BIMETALLIC DONOR-ACCEPTOR ASSEMBLIES

A series of bimetallic complexes containing an (alpha-diimine)(CO)(3)R e-I chromophore and a covalently attached ruthenium pentaammine moiety has been prepared and characterized. Ground state properties, includi ng absorption spectra and redox potentials, are consistent with very w eak metal-metal interaction in these systems. However, picosecond lumi nescence decay profiles indicate that emission from the Re --> alpha-d iimine (3)MLCT excited state is strongly quenched by attachment of the Ru center for complexes in both Re-I/Ru-II and Re-I/Ru-III oxidation states. Such behaviour is consistent with extremely rapid photoinduced intramolecular electron transfer processes, and the data are interpre ted in light of the 'superexchange' mechanism. No short-lived transien ts are observed for the Re-I/Ru-III bimetallic complexes, suggesting t hat electron transfer may occur from the (1)MLCT state in these system s.