CHROMOPHORIC FINE TUNING AND THE INTERCHROMOPHORIC COUPLING MODEL IN RUTHENIUM(II) POLYPYRIDYL COMPLEXES

The interchromophoric coupling model (J. Am. Chem. Soc. 1988, 110, 1325) succeeded in rationalizing qualitatively and quantitatively the excited-state absorption and emission properties for true mono-, bis-, and tris(diimine) chelates of Ru(II). Specifically, the weak interligand coupling between identical ligands for bis and tris complexes results in regions of localized and delocalized excitation for the singlet MLCT excited state. Spin-orbit coupling then produces localized orbital emitting states of mixed polarization. The magnitude of the Pmax (maximum excitation photoselection) is typically 0.23 for true tris and 0.34 for true bis compounds and approaches 0.5 for mono(diimine) complexes. In every case, the magnitude of Pmax depends upon the number of emitting degenerate states. These new results present data for mixed-ligand chelates in which the emitting state's degeneracy is systematically reduced from that of the true parent bis complexes. This systematic reduction in the interligand coupling between the near degenerate levels of the diimine complexes results in Pmax values ranging from 0.20 to 0.32 in a continuous fashion and consistent with the predictions of the ICC model. © 1990 American Chemical Society.