Photoinduced charge separation in R–CO2–Re(CO)3(2,2′-bipyridine) complexes. Two emitting charge transfer excited states

Abstract

Excited state properties of the newly prepared complexes R–CO₂–Re(CO)₃(2,2′-bipy), where R–CO₂⁻ = naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and acetate, were investigated by steady state and time resolved spectroscopy. The X-ray structure revealed that the R containing ligand is coordinated through the carboxylate group to Re(I). Results showed that two emitting excited states play a major role in the photophysics of the complexes. The fast component of the complexes luminescence was associated with the charge transfer excited state, MLCT, Re-to-2,2′-bipyridine, while experimental evidence led to the long lived component being attributed to a ligand-to-ligand charge transfer excited state. This emissive LLCT excited state can also evolve to a photodissociative state which ultimately produces the complex decarboxylation. On the other hand, the carboxylate bridge was shown to be able to impede connection between R and the Re(CO)₃(2,2′-bipy) chromophore.