Spectroscopy of a picosecond excited state: the S2(B1u) .tautm. S0(A1g) transition of coronene

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.

Ultrafast nonradiative transitions between higher excited states in organic molecules

“…The lifetime of the vibronic S 2 states, estimated from the homogeneous width of resonance transitions, was found to be somewhat shorter than 2 ps. This is in reasonable agreement with the results obtained by different authors 148,149 who observed fluorescence from the S 2 state of coronene under conditions of direct singlequantum excitation and with the results of measurements of the homogeneous width of fluorescence excitation lines in the Shpolskii matrices and in a supersonic jet. Such a relatively long lifetime of the S 2 state [with the energy gap DE(S 2 7S 1 ) ^5000 cm 71 ] seems to be due to high molecular symmetry and forbiddenness of the S 2 ( 1 B 1u ) ?…”

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

“…However, we cannot but treat only the visible transitions, since the bands based on the forbidden transitions are invisible or hidden by visible and stronger bands. Thus, according to the assignments by Ho et al, [1] we treat the weak absorption bands ranging from 23 000 to 28 000 cm À1 as the transition to the S 1 ( 1 B 2u ) state, the band from 28 000 to 32 000 cm À1 as that to the S 2 ( 1 B 1u ) state and those near 33 000 cm À1 as that to the S 3 ( 1 E 1u ) state.…”

“…There are a considerable amount of works on the spectroscopy of this molecule [1][2][3][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. It is known that coronene exhibits weak S 2 ( 1 B 1u ) fluorescence in addition to the S 1 ( 1 B 2u ) fluorescence in room temperature solution and in a low temperature matrix [1]. It is reported also that coronene exhibits the S 2 and possible S 3 fluorescence besides the S 1 fluorescence in the vapor phase [2].…”

The S0 → S4 transition jet-cooled fluoranthene: vibronic coupling of S4 with S3

“…No exception from the statistical limit is known for the coupling of S~ with S O for large polyatomic molecules. Among aromatic hydrocarbons only few compounds, such as azulene [10], phenanthrene [9,11,12] and coronene [13][14][15] exhibit S 2 • S~ vibronic coupling according to the statistical limit. In a recent publication [16] we showed that the S o ~ S absorption band of 1,2-benzanthracene satisfies the criteria for the statistical limit of vibronic coupling of S 3 with S 2.…”