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The photophysical and photochemical properties of the series of tris-chelate complexes Ru(bpy),(bpyz),-?+, Ru(bpy),(bpym)3-:+, R~(bpym),(bpyz)~-,2+, 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) k, and k,,, 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 k,, properties are understandable based on the energy gap law, (2) low-lying dd states strongly influence lifetimes and photochemical instabilities for the complexes Ru(bpy~)~'+, Ru(bp~m)3~+, Ru(bpy)(b~yz)~~+, Ru(bpy)(b~ym)~~+, Ru(bpym)(b~yz)~~+, Ru(bp~m)~(bpyz)~+, and Ru-(bpy)(bpym)(bpyz)*+ at room temperature, and (3) for the complexes R~(bpy),(bpyz)~+ and R~(bpy),(bpym)~+ 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.

A number of complexes of the type Re(L-L)(C0)3py+ have been prepared, where L-L is 1,lO-phenanthroline or a phenanthroline derivative containing methyl or phenyl groups and py is pyridine. All of the complexes are highly emissive at room temperature in solution or at 77 K in a glass, and the room-temperature luminescence data are consistent with emission from a 3MLCT state. The emission maximum ranges from 510 to 548 nm in CH*Clz, depending on L-L, and a linear relationship between A, , , and the electrode potentials for oxidation and reduction is evident. Lifetimes in acetonitrile are of the order of several microseconds at room temperature (1.6-1 3 ps), and emission quantum yields are very high (0.17-0.29). Results of photophysical measurements performed at low temperature indicate the presence of two unequilibrated emitting states, a 3MLCT and a 3LC (ligand-centered) state. Time-resolved spectra have established that the 3LC state is the longer-lived of the two and gives a structured spectrum similar to that of the uncoordinated ligand L-L. Both states show a dependence on the substitution pattern, and the contribution of each is determined by the particular L-L. Trends in the room-temperature data may also be accounted for by invoking a multistate model: however, the states are in thermal equilibrium under these conditions.

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