Multiple fluorescence and the electronic relaxation processes of coronene vapor: The fluorescence from the S1, S2, and S3 states

Fluorescence and excitation spectra of coronene vapor have been measured under different conditions. Weak emission which can be regarded as the fluorescence from the third excited singlet state, S3(1E1u), was observed in addition to the S1(1B2u) and S2(1B1u) fluorescence. The observed S2 and S3 fluorescence are substantially different from those reported previously for coronene vapor. Addition of oxygen resulted in significant decrease of the S1 fluorescence intensity, but did not affect the S2 fluorescence intensity, indicating the faster decay rate of the S2 state than that of S1. Excitation energy dependence of the S1, S2 and S3 fluorescence quantum yields (ΦF(S1), ΦF(S2) and ΦF(S3), respectively) revealed that ΦF(S1) decreases with increasing excitation energy, while ΦF(S2) and ΦF(S3) increase significantly. The quantum yield ratios, ΦF(S2)/ΦF(S1) and ΦF(S3)/ΦF(S2), obtained as a function of excitation energy are correlated with the ratios of the relative internal conversion rates.