ZERO-FIELD SPLITTING OF THE GROUND AND EXCITED TRIPLET-STATES OF 2-NAPHTHYLPHENYLCARBENE STUDIED BY HOLE-BURNING ON TRIPLET-TRIPLET FLUORESCENCE EXCITATION-SPECTRA

Spectral holes were burned in the two main lines of the triplet-triple t 0-0 fluorescence excitation spectrum of 2-naphthylphenylcarbene in n -hexane at 1.8 K. For the line assigned to pseudo-E/trans conformer, t he central hole at the frequency of burning light has several narrow c omponents separated by 0.3 +/- 0.05 and 1.0 +/- 0.1 GHz and a satellit e doublet line on the low energy side, 14.5 +/- 0.5 and 15.5 +/- 0.5 G Hz away, For the line assigned to the pseudo-Z/cis conformer, the cent ral hole is accompanied by holes burned on the low energy side, 0.8 +/ - 0.1, 5.2 +/- 0.1, 11.9 +/- 0.1 and 16.2 +/- 0.1 GHz away. The hole-b urning pattern is explained by a model taking into account the zero-fi eld splitting (ZFS) of the ground T-0 and excited T-1 triplet states a s well as the selectivity of excitation relaxation by the intersystem crossing channel. Analysis provides information about the ZFS paramete rs of the T-1 state. For the pseudo-E/trans 2-NPC they are: D-0 = 0.47 +/- 0.02 cm(-1), E(0) = 0.017 +/- 0.003 cm(-1), D-1 = 0.038 +/- 0.003 cm(-1) and E(1) = 0.005 +/- 0.001 cm(-1).