S-0 AND S-1 ELECTRONIC STATES OF 2-VINYLNAPHTHALENE - A PSEUDO POLYENE

High resolution S-1 <-- S-0 fluorescence excitation experiments on 2-v inylnaphthalene (2VN) show that the two electronic origins which appea r in analogous low resolution spectra are the 0(0)(0) bands of the syn and anti conformers of 2VN. Additionally, it was found that both orig ins are a-axis polarized; i.e., that the S-1 <-- S-0 optical transitio n moments are parallel to the long axes of both conformers. This infor mation, together with the measured rotational constants, partial vibra tional analyses of the low resolution spectra, and the results of ab i nitio calculations, strongly suggests that the S-1 <-- S-0 transition is ''polyene-like''; i.e., that significant bond-order reversal accomp anies the absorption of the photon. This view is supported by the appr oximate vinyl torsional potential energy surfaces of both s- and a-2VN that have been derived from the data.