TRIPLET TRIPLET FLUORESCENCE AND SPIN POLARIZATION - DIPHENYLCARBENE AND DIBENZOCYCLOHEPTADIENYLIDENE

The laser-induced fluorescence spectrum of diphenylcarbene (DPC) obtained from four independent precursors is blue-shifted in low-temperature glasses relative to liquid solution. The spectrum of the less conformationally mobile ethano-bridged carbene dibenzocycloheptadienylidene (DBC) is virtually the same in solution and in glasses. The fluorescence spectra of 3DPC* and 3DBC* in Shpol'skii matrices have been recorded between 4.2 and 77 K. While DBC exhibits only one well-resolved spectrum, DPC presents a sharp spectrum, plus a broad blue-shifted one. The fluorescence decays of 3DPC* and 3DBC* measured on the sharp spectra were found to be nonexponential and influenced by the presence of a weak external magnetic field in a manner similar to that of the m-xylylene biradicals. The fluorescence decay of 3DPC* recorded on the broad spectrum is exponential and remains unchanged under this field. © 1990 American Chemical Society.