Spectroscopic studies of 12-oxo-5(12H)-naphthacenylidene and 7H-benz[de]anthracen-7-ylidene in Shpolskii matrixes at 5 K

The triplet-triplet fluorescence and fluorescence excitation spectra of two new, planar diaryl carbenes in n-hexane and n-heptane were studied at cryogenic temperatures. Fluorescence decays were fitted to three exponential functions. Fluorescence decays of 12-oxo-5(12H)-naphthacenylidene were sensitive to the presence of a magnetic field, and this dependence allowed the estimation of the zero field splitting parameters (D) of the excited triplet state of this compound, which were 0.037 +/- 0.010 and 0.03 +/- 0.015 cm(-1) for the low- and high-energy sites, respectively. These results are corroborated by computational studies of the ground-state preferences and the triplet excitation energies.