Zero-Field Splitting of the Electronic Ground and Lowest Excited Triplet States of 2,2-Dinaphthylcarbene in <i>n</i>-Hexane at 1.7 K

Abstract

The triplet−triplet fluorescence spectra of a new carbene, 2,2-dinaphthylcarbene in n -hexane and n -heptane, were studied at cryogenic temperatures. Synthesis of the carbene precursor, 2,2-dinaphthyldiazomethane, is described. Spectral holes were burned within the inhomogeneous 0,0 fluorescence excitation line assigned to the pseudo-E/trans conformer. The complicated pattern 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 observation of antiholes was attributed to the extremely long spin−lattice relaxation time in the T 0 state. The analysis provided direct information about the ZFS parameters of the T 0 and T 1 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 .