Evidence for S1/S2 electronic state mixing in the S1 ←l S0 fluorescence excitation spectrum of 1-naphthol

Rotationally resolved fluorescence excitation spectra of two vibronic bands at ΔE = 410.5 and 414.9 cm−1 in the S1 ← S0 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 S1 electronic state to the S2 electronic state which may influence the proton transfer behavior of 1-napththol.