LASER-INDUCED FLUORESCENCE OF MOLYBDENOCENE AND TUNGSTENOCENE IN LOW-TEMPERATURE MATRICES

The reactive metallocenes, tungstenocene and molybdenocene (M(eta(5)-C 5H5)(2); M = Mo, W), have been generated by photolysis of the correspo nding dihydride complexes, M(eta(5)-C5H5)(2)H-2, in argon and nitrogen matrices at 12 K. The metallocenes have been probed by laser-induced fluorescence with a pulsed tunable laser and by UV/vis absorption spec troscopy. Structured emission is observed from the LMCT excited states (lifetimes < 10 ns). The spectra are complicated by multiple sites/co nformers, but emission spectra of a single site/conformer may be obtai ned with appropriate selection of matrix and excitation wavelength. Co rresponding excitation spectra are measured from the area of selected emission peaks as a function of excitation wavelength. Vibrational pro gressions are dominated by the ring-metal-ring symmetric stretching mo de (nu(4) approximate to 300 cm(-1)). Nevertheless, this mode changes in frequency by less than or equal to 4 cm(-1) (less than or equal to 1.3%) in the LMCT excited state. The best-resolved peaks have a full w idth at half-maximum of ca. 10 cm(-1). Most of the emission is vibrati onally fully relaxed, but weak emission peaks arising from nu' = 1 sta tes are found for MoCp(2) in N-2 matrices.