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

Abstract

Spectral holes were burned within the inhomogeneous (0,0) fluorescence excitation line of the T0→T1 transition of 7H-benz[de]anthracen-7-ylidene in an n-hexane matrix at 1.7 K. The complicated spectrum of the obtained holes was interpreted with a model taking into account the zero-field splitting (ZFS) of both the triplet states contributing to the transition, the enforced planar symmetry of the carbene, and the domination of internal conversion in the relaxation of the excited T1 state. Analysis of the hole-burning spectra produced the following ZFS parameters of the ground T0 and excited T1 states: D0 = (0.274 ± 0.001) cm-1 + E1, E0 = (0.0292 ± 0.0002) cm-1 + E1 and D1 = (0.0168 ± 0.0002) cm-1 + E1. The number of possible transitions between different spin sublevels is reduced as a consequence of the symmetry plane in the carbene and one of the ZFS parameters, we chose the smallest, E1, cannot be estimated. The ZFS parameters of the T0 state were also estimated by conventional matrix ESR and were in good agreement with the results of the hole burning experiments.