Picosecond Time-Resolved Absorption and Emission Studies of the Singlet Excited States of Acenaphthylene

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 (S{sub 2}) is found to compete with the nonradiative decay of this state. A lifetime of <40 ps is suggested for the S{sub 2} state. The major deactivation pathway of the S{sub 1} state is identified as an efficient S{sub 1} {yields} S{sub 0} internal conversion. While internal conversion accounts for most of the deactivation of the S{sub 1} state, fluorescence with a very low quantum yield is observed. Transient absorption on the picosecond time scale is assigned to S{sub 1} {yields} S{sub n} 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.