METAL-TO-LIGAND CHARGE-TRANSFER (MLCT) PHOTOCHEMISTRY - EXPERIMENTAL-EVIDENCE FOR THE PARTICIPATION OF A HIGHER LYING MLCT STATE IN POLYPYRIDYL COMPLEXES OF RUTHENIUM(II) AND OSMIUM(II)

Evidence is presented which supports the existence of a thermally accessible, higher lying metal-to-ligand charge-transfer (MLCT) excited state for polypyridyl complexes of Ru(II) and Os(II). This state is shown to exist for complexes both in solution and in the solid state. It is typically found to occur at 300-800 cm-1 above the lowest lying MLCT state and to have a decay rate constant of 106-108 s-1. This decay rate constant is about 10 times faster than the decay rate constant for the next lower lying MLCT state. The decay process appears to be almost completely nonradiative with the radiative decay rate constant estimated to be 106 s-1 or slower. The higher lying MLCT states can make a significant contribution to nonradiative decay at room temperature. © 1990 American Chemical Society.