Zero-field splitting of the electronic ground and lowest excited triplet states of 2,2-dinaphthylcarbene in n-hexane at 1.7 K

The triplet-triplet fluorescence spectra of a new carbene, 2,2-dinaphthylca rbene in n-hexane and n-heptane, were studied at cryogenic temperatures. Sy nthesis of the carbene precursor, 2,2-dinaphthyldiazomethane, is described. Spectral holes were burned within the inhomogeneous 0,0 fluorescence excit ation line assigned to the pseudo-E/trans conformer. The complicated patter n of burned holes was interpreted with a model taking into account the zero -field splitting (ZFS) of the ground T-0 and excited T-1 triplet states and the selectivity of the intersystem crossing channel. The unusual observati on of antiholes was attributed to the extremely long spin-lattice relaxatio n time in the T-0 state. The analysis provided direct information about the ZFS parameters of the To and Ti states: E-0 = 0.022 +/- 0.001 cm(-1), D-0 = 0.477 +/- 0.001 cm(-1), E-1 = 0.006 +/- 0.0002 cm(-1) and D-1 = 0.043 +/- 0.0005 cm(-1).