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

Rotationally resolved fluorescence excitation spectra of two vibronic bands at Delta E = 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 degrees with the a inertial axis, the same as the origin band, whereas the corresponding angle of the 414 cm(-1) band is +55 degrees. 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-naphthol.