Picosecond time-resolved absorption and emission studies of the singlet excited states of acenaphthylene

Abstract

Radiative and nonradiative processes in acenaphthylene have been examined by a combination of steady-state and picosecond time-resolved emission and transient absorption measurements. Fluorescence from a higher excited state (S2) is found to compete with the nonradiative decay of this state. A lifetime of < 40 ps is suggested for the S2 state. The major deactivation pathway of the S1 state is identified as an efficient S1 \/\/\/\→ S0 internal conversion, the rate constant of which is measured to be 2.8 × 109 s-1. While internal conversion accounts for most of the deactivation of the S1 state, fluorescence with a very low quantum yield (∼6 × 10-4) is observed. Transient absorption on the picosecond time scale is assigned to S1 → Sn absorption. The spectra recorded immediately after excitation are found to have a contribution from vibrationally unrelaxed molecules. A rough estimate for the vibrational relaxation rate is also made. © 1990 American Chemical Society.