The excited-state dynamics of phenylvinyl acetylene (1-phenyl-1-buten-3-yne, PVA) have been studied using laser-induced fluorescence spectroscopy, ultraviolet depletion spectroscopy, and the newly developed method of ultraviolet population transfer spectroscopy. Both isomers of PVA (E and 2) show a substantial loss in fluorescence intensity as a function of excitation energy. This loss in fluorescence was shown to be due to the turn-on of a nonradiative process by comparison of the laser-induced fluorescence spectrum to the ultraviolet depletion spectrum of each isomer, with a threshold 600 cm(-1) above the electronic origin in Z-PVA and 1000 cm(-1) above the electronic origin in E-PVA. Ab initio and density functional theory calculations have been used to show that the most likely source of the nonradiative process is from the interaction of the pi pi(star) state with a close lying pi sigma(star) state whose minimum energy structure is bent along the terminal CCH group. Ultraviolet population transfer spectroscopy has been used to probe the extent to which excited-state isomerization is facilitated by the interaction with the pi sigma(star) state. In ultraviolet population transfer spectroscopy, each isomer was selectively excited to vibronic levels in the S, state with energies above and below the threshold for fluorescence quenching. The ultraviolet-excited populations are then recooled to the zero point levels using a reaction tube designed to constrain the supersonic expansion and increase the collision cooling capacity of the expansion. The new isomeric distribution was detected in a downstream position using resonant-2-photon ionization spectroscopy. From these spectra, relative isomerization quantum yields were calculated as a function of excitation energy. While the fluorescence quantum yield drops by a factor of 50-100, the isomerization quantum yields remain essentially constant, implying that the nonradiative process does not directly involve isomerization. On this basis, we postulate that isomerization occurs on the ground-state potential energy surface after internal conversion. In these experiments, the isomerization to naphthalene was not observed, implying a competition between isomerization and cooling on the ground-state potential energy surface.