Two-photon excitation of rhenium metal-ligand complexes

We describe the emission spectral properties of two rhenium metal±ligand complexes with one and two-photon excitation, Re(bpy)2(CO)3Cl and [Re(bpy)(CO)3CH3CN] ‡, where bpy is 2,20-bipyridyl and CH3CN is acetonitrile. Similar emission spectra and intensity decay times characteristic of the metal-to-ligand charge transfer state were observed for oneand two-photon excitation. The lifetime and quantum yield of the acetonitrile complex are approximately 14-fold higher than that of the chloride complex. Both complexes display high anisotropies near 0.33 in frozen solution with one-photon excitation. Two-photon excitation results in anisotropies about 40% larger, consistent with the increased photoselection expected for two-photon absorption. These complexes display single rotational correlation times in glycerol, but the correlation time of the charged acetonitrile complex is 3 to 4-fold larger. These results show that rhenium complexes can be used as hydrodynamic probes with oneor two-photon excitation. # 1999 Elsevier Science S.A. All rights reserved.