Molecular and Electronic Structures of the Short-Lived Excited Triplet State of Tropone

Abstract

Time-resolved electron paramagnetic resonance experiments on the short-lived T 1 state of nonphosphorescent 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 tensor. 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 ππ* 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 S 0 states arises from the change of the potential surfaces due to the antibonding character of the π* orbital at the C 4 -C 5 bond in the T 1 state.

Anisotropic Intersystem Crossing from the Upper Excited Triplet States of Anthracenes: Two-laser Time-Resolved EPR Study

“…The time-resolved EPR technique has been successfully applied to investigate the nature of short-lived excited triplet states. − Since electron spin polarization (ESP) reflects the relaxation pathway in the excited states, the phase of ESP as well as temporal behaviors provides the information on the excited-state dynamics. Almost all studies have been focused on the spin dynamics in the intersystem crossing (ISC) process between the lowest excited singlet (S 1 ) and triplet (T 1 ) states.…”