Zero-field splitting of the triplet ground and excited states of 7H-benz[de]anthracen-7-ylidene in n-hexane at 1.7 K: A hole burning study

Spectral holes were burned within the inhomogeneous (0,0) fluorescence exci tation line of the T-0-->T-1 transition of 7H-benz[de]anthracen-7-ylidene i n an n-hexane matrix at 1.7 K. The complicated spectrum of the obtained hol es was interpreted with a model taking into account the zero-field splittin g (ZFS) of both the triplet states contributing to the transition, the enfo rced planar symmetry of the carbene, and the domination of internal convers ion in the relaxation of the excited T-1 state. Analysis of the hole-burnin g spectra produced the following ZFS parameters of the ground T-0 and excit ed T-1 slates: D-0 = (0.274 +/- 0.001) cm(-') + E-1, E-0 = (0.0292 +/- 0.00 02) cm(-1) + E-1 and D-1 = (0.0168 +/- 0.0002) cm(-1) + E-1. The number of possible transitions between different spin sublevels is reduced as a conse quence of the symmetry plane in the carbene and one of the ZFS parameters, we chose the smallest, E-1, cannot be estimated. The ZFS parameters of the T-0 state were also estimated by conventional matrix ESR and were in good a greement with the results of the hole burning experiments.