Primary photoisomerization reactions of 6-phenoxy-5,12-naphthacenequinone

Primary processes of 6-phenoxy-5,12-naphthacenequinone (PhNQ) photoisomeriz ation initiated by femtosecond light pulses of wavelength 307 nm are studie d experimentally and theoretically. The kinetics of photoinduced absorption spectra in the range from 420 to 540 nm is explored at times up to 100 ps. Energies of the excited states of the A and B modifications of PhNQ, as we ll as the dependences of the potential energies of excited-state PhNQ on th e reaction coordinate, were calculated by the semi-empirical CINDO/S-CI met hod, while the molecular geometry was optimized by the AM1 method. It is fo und that despite a considerable store of the electron energy, the photochem ical isomerization of molecules promoted to the S-3 state proceeds exclusiv ely via triplet states. A mechanism of primary photoisomerization reactions of 6-phenoxy-5,12-naphthacenequinone is proposed.