Four tricarbonyl(histidine)(diimine)rhenium(I) complexes have been prepared, where diimine is 2,2′-bipyridine (bpy), 4,4′-dicarboxyl-2,2′-bipyridine (bpy(COO)2)2-, 1,10-phenanthroline (phen), and disulfonate 4,7-diphenyl-1,10-phenanthroline (phen-(phSO3)2)2-. All complexes exhibit metal-to-ligand charge-transfer (MLCT) absorption in the 350-380 nm range. Excitation into the MLCT absorption bands results in orange luminescence. The emission maxima for these complexes range from 580 to 625 nm in aqueous solution at room temperature. The excited-state energy, broad emission profiles, and long excited-state lifetimes indicate emission from a 3MLCT state. The complexes with phen-type diimine ligands have much longer lifetimes than those with bpy-type diimine ligands: Re(phen(phSO3)2)(CO)3(His)-, τ = 170 ns; Re(phen)(CO)3(His)+, τ = 100 ns.
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