Photochemistry and photophysics of coordinatively unsaturated copper(I) and platinum(II) complexes

Previous studies of coordinatively unsaturated copper(I) bis-phenanthroline complexes indicated that the triplet charge transfer state is quenched via a type exciplex mechanism in the presence of Lewis bases. While exciplex formation is common in organic species, this is a relatively rare quenching mechanism for transition metal compounds. It was sought to verify this quenching mechanism for the copper(I) bis-phenanthrolines. The activation parameters of copper(I) bis-phenanthrolines with an expanded series of Lewis bases were analyzed through temperature dependent quenching experiments. It was found that in all cases a negative enthalpy of activation resulted, although the magnitude varied greatly. Next the activation parameters of processes involving energy and electron transfer mechanisms were determined. In both cases a positive enthalpy of activation resulted. This allowed the conclusion that a negative enthalpy of activation can be taken as evidence for quenching by exciplex formation in these systems. Additionally, the absorption and emission properties of a series of platinum(II) terpyridine complexes were carried out. These complexes exhibit some degree of dimerization in water, and show only slight dimer formation in methanol, ethanol/methanol, or acetonitrile. The formation constants of the dimer in the various solvents, as well as monomer and dimer absorptivities were determined using the program SPECDEC. The emission of these complexes falls into two general areas. At around 450-520 nanometers, structured triplet $\pi\pi$* emission is seen, and at low energies, a broad band emission from either a charge transfer or a dd state is seen. Quantum yields, temperature dependent emission, and temperature dependent lifetimes were determined for two representative examples of complexes exhibiting broad band emission