S2 fluorescence from picene vapor

Fluorescence, fluorescence excitation and absorption spectra of picene have been measured in the vapor phase. It is shown that picene vapor exhibits weak fluorescence from the S2(π, π∗) state in addition to strong S1(π, π∗) fluorescence. The S2/S1 fluorescence yield ratio is evaluated to be approximately 1.3 × 10−2 following the excitation into the S3 state. It is shown that the relative S2 fluorescence quantum yield increases with increasing excitation energy, while the S1 fluorescence yield is nearly invariant. Mechanism of the appearance of the S2 fluorescence of picene vapor is discussed.