Evidence for S 1/S 2 electronic state mixing in the S 1 ← l S 0 fluorescence excitation spectrum of 1-naphthol

Abstract

Rotationally resolved fluorescence excitation spectra of two vibronic bands at ΔE = 410.5 and 414.9 cm −1 in the S 1 ← S 0 electronic transition of trans-1-naphthol have been recorded and analyzed. The analysis reveals that the in-plane transition dipole moment of the 410 cm −1 band makes an angle of −36° with the a inertial axis, the same as the origin band, whereas the corresponding angle of the 414 cm −1 band is +55°. Additionally, the spectrum of the 414 cm −1 band is perturbed. These effects are attributed to a coupling of the 414 cm −1 vibrational level of the S 1 electronic state to the S 2 electronic state which may influence the proton transfer behavior of 1-napththol.