Stokes and anti-Stokes fluorescence of 1,12-benzoperylene in solution

Extensive observations of the Stokes and anti-Stokes fluorescence spectra of 1,12-benzoperylene in n-heptane solution from −90 to +90°C are reported and analyzed. Corresponding absorption spectra over the same temperature range are used in the assignment of the vibronic states and transitions. The normal fluorescence spectrum has five bands, corresponding to the S01→S00, S10, S20, S30, S40 transitions (SVE refers to a singlet electronic state SE in a vibrational level V), which are the origins of symmetric ?5 vibrational progressions. Three bands beyond the S01→S00 transitions are identified as S11, S21, S31→S00 hot fluorescence and one band as S02→S00 fluorescene, and these are the origins of similar ?5 progressions. It is proposed that the S01→Sm0(m≠0), Sn1→S00 (n≠0), and S01→S00 transitions are induced by vibronic coupling to allowed Sm2→Sm0, S02→S00, and S12→S00 transitions, respectively. The S02→S00 fluorescence is partly directly excited and partly thermally excited from S01. Separation of these two components leads to an evaluation of the S02 lifetime (21±4 ps) and the S02→Sn1 internal conversion rate (4.8±0.8×1010 s−1).