Synthetic Control of Excited-State Properties. Tris-Chelate Complexes Containing the Ligands 2,2′-Bipyrazine, 2,2′-Bipyridine, and 2,2′-Bipyrimidine

Abstract

The photophysical and photochemical properties of the series of tris-chelate complexes Ru(bpy)n(bpyz)3_n2+, Ru(bpy)n(bpym)3_n2+, Ru(bpym)n(bpyz)3-n2+, and Ru(bpy)(bpym)(bpyz)2+ (n = 0, 1, 2, 3; bpy = 2,2′-bipyridine, bpyz = 2,2′-bipyrazine, bpym = 2,2′-bipyrimidine) are described. From the results of temperature-dependent lifetime (210–345 K) and room-temperature emission quantum yield measurements have been obtained: (1) kr and knr, the radiative and nonradiative decay rate constants for the emitting MLCT manifold and (2) kinetic parameters which suggest the intervention of additional excited states. The significant points of the study are the following: (1) trends in knr properties are understandable based on the energy gap law, (2) low-lying dd states strongly influence lifetimes and photochemical instabilities for the complexes Ru(bpyz)32+, Ru(bpym)32+, Ru(bpy)(bpyz)22+, Ru(bpy)(bpym)22+, Ru(bpym)(bpyz)22+, Ru(bpym)2(bpyz)2+, and Ru(bpy)(bpym)(bpyz)2+ at room temperature, and (3) for the complexes Ru(bpy)2(bpyz)2+ and Ru(bpy)2(bpym)2+ there is no evidence for low-lying dd states and these and/or related mixed-ligand complexes may provide a basis for a new series of photochemically stable Ru-polypyridyl chromophores. © 1984, American Chemical Society. All rights reserved.