Molecular and electronic structures of the short-lived excited triplet state of tropone

Time-resolved electron paramagnetic resonance experiments on the short-lived Ti state of nenphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tenser. The spin density distribution, C-H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T-1 state of tropone mainly has a (3) pi pi* configuration and holds its molecular structure of C-2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck-Condon factor between the T-1 and the So states arises from the change of the potential surfaces due to the antibonding character of the pi* orbital at the C-4-C-5 bond in the T-1 state.