PHOTOPHYSICAL PROPERTIES OF RHENIUM(I) TRICARBONYL COMPLEXES CONTAINING ALKYL-SUBSTITUTED AND ARYL-SUBSTITUTED PHENANTHROLINES AS LIGANDS

A number of complexes of the type Re(L-L)(CO)3Py+ have been prepared, where L-L is 1,10-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 5 1 0 to 548 nm in CH2Cl2, depending on L-L, and a linear relationship between lambda(max) and the electrode potentials for oxidation and reduction is evident. Lifetimes in acetonitrile are of the order of several microseconds at room temperature (1.6-13 mus), 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.