Spectroscopic Characterization of Structural Isomers of Naphthalene : (E)-and (Z)-Phenylvinylacetylene

Near-pure samples of (E)-phenylvinylacetylene ((E)-PVA) and (Z)-phenylvinylacetylene ((Z)-PVA) were synthesized, and their ultraviolet spectroscopy was studied under jet-cooled conditions. The fluorescence excitation and UV−UV holeburning (UVHB) spectra of both isomers were recorded. The S0−S1 origin of (E)-PVA occurs at 33 578 cm−1, whereas that for (Z)-PVA occurs at 33 838 cm−1, 260 cm−1 above that for (E)-PVA. The present study focuses primary attention on the vibronic spectroscopy of (E)-PVA. Single vibronic level fluorescence spectra of many prominent bands in the first 1200 cm−1 of the S0−S1 excitation spectrum of (E)-PVA were recorded, including several hot bands involving low-frequency out-of-plane vibrations. Much of the ground-state vibronic structure observed in these spectra was assigned by comparison with styrene and trans-β-methylstyrene, assisted by calculations at the DFT B3LYP/6-311++G(d,p) level of theory. Both S0 and S1 states of (E)-PVA are shown to be planar, with intensity appearing ...