The excited-state dynamics of Re(CO)3Cl(dcbpy) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) in dimethyl formamide (DMF) solution and on the surface of ZrO2 and TiO2 nanocrystalline thin films were studied using femtosecond IR spectroscopy. For Re(CO)3Cl(dcbpy) in DMF solution, a long-lived metal-to-ligand charge-transfer (MLCT) state with a lifetime of > 1 nsec was observed after 400-nm excitation of the MLCT band. The frequencies for the CO stretching bonds were blue-shifted compared with those in the ground state, which was consistent with the MLCT nature of the excited state. Rapid spectral evolution of the excited-state CO stretching bands was observed within the first 12 psec. For Re(CO)3Cl(dcbpy) on ZrO2 thin films, a similar MLCT state was observed. However, the spectral blue shift was much less pronounced and occurred on a faster time scale. Vibrational relaxation was suggested as the primary contribution to the spectral evolution of Re(CO)3Cl(dcbpy) on the ZrO2 films, whereas both vibrational relaxation and solvation of the MLCT state contributed to the spectral evolution in DMF solution. The excited-state decay rate of Re(CO)3Cl(dcbpy) on ZrO2 films was faster than the rate in DMF and increased with higher excitation power. Broad mid-IR absorption of injected electrons was observed for Re(CO)3Cl(dcbpy)-sensitized TiO2 thin films. The rise time of the electron absorption signal in TiO2 was < 100 fsec. The adsorbate CO stretching bands and the detailed information about the electron-injection process that can be obtained from the adsorbate vibrational spectra were also discussed.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry