No abstract

The S2(*B1u) -* S0('Alg) fluorescence spectrum of coronene in solution, obtained by using both single-and two-photon excitation, is reported. The spectra, which depend on the excitation conditions, show that even at 300 K vibrational relaxation is substantially incomplete on the time scale of the S2 lifetime. Single site excitation spectroscopy at 12 K in «-heptane has been used for vibrational frequency assignments. With the exception of a weak, matrix-induced resonance at 370 cm"1, the set of vibronically active modes which defines the S2 •*-* S0 spectrum is found to be distinct from that for S, +» S0, although there is some overlap with the phosphorescence spectrum. The minimum line widths observed in fluorescence excitation of S0 -* S2 coronene were ~5 cm"1.