PHOTOPHYSICAL PROPERTIES OF TRICARBONYL(HISTIDINE)(DIIMINE)RHENIUM(I)COMPLEXES IN AQUEOUS-SOLUTION

Four tricarbonyl(histidine) (diimine)rhenium(I) complexes have been pr epared, where diimine is 2,2'-bipyridine (bpy), 4,4'-dicarboxyl-2,2'-b ipyridine,2'-bipyridine (bpy(COO)(2))(2-), 1,10-phenanthroline (phen), and disulfonate 4,7-diphenyl-1,10-phenanthroline (phen(PhSO(3))(2))(2 -). All complexes exhibit metal-to-ligand charge-transfer (MLCT) absor ption in the 350-380 nm range. Excitation into the MLCT absorption ban ds results in orange luminescence. The emission maxima for these compl exes range from 580 to 625 nm in aqueous solution at room temperature. The excited-state energy, broad emission profiles, and long excited-s tate lifetimes indicate emission from a (3)MLCT state. The complexes w ith phen-type diimine ligands have much longer lifetimes than those wi th bpy-type diimine ligands: Re(phen(phSO(3))(2))(CO)(3)(His)(-), tau = 170 ns; Re(phen)(CO)(3)(His)(+), tau = 100 ns.