NEAR-INFRARED LUMINESCENCE SPECTROSCOPY OF COBALTOCENE DOPED INTO SINGLE-CRYSTALS OF RUTHENOCENE

Near-infrared luminescence was observed from cobaltocene molecules dop ed into single crystals of ruthenocene. The spectrum and lifetime of t he luminescence under UV excitation were studied between 6 and 100 K. Below 30 K, the cobaltocene luminescence is weak compared to that of t he ruthenocene host lattice but becomes dominant above 50 K, evidence for a thermally induced energy transfer from ruthenocene to cobaltocen e. The activation energy is estimated to be 140(40) cm(-1) from lumine scence decay curves. Selective excitation revealed the cobaltocene lum inescence to be a broad, unstructured but highly asymmetric band with a maximum at 13 100 cm(-1) (760 nm). Comparison with the absorption sp ectrum determines the energy of the lowest excited state to be 14 050 cm(-1). Calculated luminescence spectra using time-dependent quantum-m echanical calculations demonstrate that the highly asymmetric shape is due to a dynamic Jahn-Teller effect in the ground state along a high- frequency ligand-centered mode. The calculations also show an elongati on of the Co-cyclopentadienyl bond length of 0.07 Angstrom in the emit ting state.