Spectroscopy and Photophysics of Structural Isomers of Naphthalene: Z-Phenylvinylacetylene

Abstract

The fluorescence spectroscopy of Z-phenylvinylacetylene (Z-PVA) has been studied under jet-cooled conditions. The laser-induced fluorescence (LIF) spectrum shows vibronic activity up to 600 cm(-1) above the pi pi* electronic origin at 33 838 cm(-1). In contrast, the single vibronic level fluorescence spectrum of the electronic origin shows strong intensity in transitions ending in ground state levels at least 1200 cm(-1) above the ground state zero-point level. The double-resonance technique of ultraviolet depletion (UVD) spectroscopy was used to show that there are strong absorptions in Z-PVA that are not observed in the LIF spectrum due to the turn of a nonradiative process in this electronic state. The LIF and UVD spectra were compared quantitatively to calculate the relative single vibronic level fluorescence quantum yields. Upon inspection, there are some indications of state specific effects; however, the nature of these effects is unclear. Ab initio and density functional theory calculations of the ground and excited states were used to map the first two excited states of Z-PVA along the C[triple bond]CH bending coordinate, determining them to be pi pi* and pi sigma*, respectively, in character. The crossing of these two states is postulated to be the underlying reason for the observed loss in fluorescence intensity 600 cm(-1) above the pi pi* origin. The spectroscopy of Z-PVA has been compared to the previously characterized E isomer of phenylvinylacetylene [Liu, C. P., Newby, J. J., Muller, C. W., Lee, H. D. and Zwier, T. S. J. Phys. Chem. A 2008, 112 (39), 9454.].