Rotationally resolved S1<-- S0 electronic spectra of fluorene, carbazole, and dibenzofuran: evidence for Herzberg-Teller coupling with the S2 state.
Rotationally resolved fluorescence excitation spectra of the S1 <-- S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1 <-- S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.
Yi
John T
JT
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Alvarez-Valtierra
Leonardo
L
Pratt
David W
DW