Laser-induced fluorescence excitation spectrum and CF3 torsional potential energy function of 7-amino-4-(trifluoromethyl)coumarin in its S-1 electronic excited state

Abstract

The laser-induced fluorescence excitation spectrum of 7-amino-4-(trifluoromethyl)coumarin in a supersonic jet has been recorded in the 340-352 nm region. The electronic band origin was observed at 28622.8 cm(-1). Vibrational assignments for the three fundamental low-frequency modes and eight combination bands have been made for the S-1 electronic excited state. The out-of-plane vibrations of this molecule have been characterized from the low-frequency assignments of the spectrum. The periodic potential energy function for the CF3 torsion, which satisfactorily fits the observed data, were also determined to be V(phi)=95X(1-cos3 phi)-32X(1-cos6 phi) where phi is the torsional angle. The relatively low torsional barrier of 99 cm(-1) in S-1 state could be explained by the small steric interactions between the functional groups attached to a bicyclic ring.