Ligand control of the mechanism of photosensitization by copper(I) compounds

Article abstract of DOI:10.1021/ic00132a015

Formation of a ground-state complex between CuBr(py)(PPh₃) (py is pyridine) and norbornadiene (NBD) occurs upon mixing the compounds in benzene. Irradiation of the complex with 313-nm light generates the valence isomer quadricyclene (Q) with moderate observed quantum efficiency. This efficiency varies with the nature and concentration of excess ligands present in solution. Spectral studies reveal that this behavior arises from the creation of new Cu(I) species whose sensitization properties differ from those of CuBr(py) (PPh₃). Thus a sufficient excess of triphenylphosphine converts the parent compound to CuBr(PPh₃)₃. The latter species functions as an effective sensitizer for Q production but by a pathway involving bimolecular interaction of photoexcited CuBr(PPh₃)₃ with ground-state NBD. These results demonstrate that the mechanism of sensitization by Cu(I) can be controlled by the judicious addition of ligands to the system.