LASER-INDUCED FLUORESCENCE OF RHENOCENE IN LOW-TEMPERATURE MATRICES -SELECTIVE EXCITATION AND EMISSION

Rhenocene, Re(eta(5)-C5H5)(2), has been generated by photolysis of Re( eta(5)-C5H5)(2)H isolated in nitrogen and argon matrices at 12 K, and has been studied by laser-induced fluorescence with a pulsed tunable l aser. The emission lifetime of the lowest LMCT excited state is (71.9 +/- 1.3) ns in nitrogen and (69.3 +/- 1.4) ns in argon matrices. The e mission and excitation spectra are far simpler and much better resolve d than the UV/vis absorption spectrum, because the laser selects indiv idual sites/conformers in the matrix (or groups of sites with very sim ilar absorptions). Vibrational progressions are detected which are bas ed on the ring-metal-ring stretching mode, nu(3), and combinations of that mode with the symmetric ring breathing mode, nu(2), and the symme tric C-H deformation mode, nu(3). In the LMCT excited state, there is an increase in nu(4) of 5% and a decrease in nu(3) (9%) and nu(2) (3%) , consistent with transfer of an electron from a ligand pi-orbital to a metal-ligand bonding orbital.