Ground and excited singlet states of 2-vinylnaphthalene, ethyl-2-naphthylacrylate and N,N-dimethyl-2-naphthylacrylamide in solution

The molecular conformation, spectroscopy and photochemical behavior of 2-vinylnaphthalene and its acrylate and acrylamide analogs were investigated. All three molecules exist as mixtures of syn and anti conformers. Ground state conformer populations were studied by nuclear Overhauser effect (NOE) spectroscopy and MM2 calculations. The electronic structure and spectra of the syn and anti conformers were investigated by INDO/S-SCF-CI calculations and were found to be very similar. Dual exponential fluorescence decay is observed for these molecules and is attributed to fluorescence from both the syn and anti conformers. The absence of a wavelength dependence for the fluorescence excitation and emission spectra provides experimental evidence that the syn and anti conformers have similar spectra. Photoisomerization of the acrylate and acrylamide occurs via a triplet state mechanism. Quenching of the acrylate singlet states by amines is more rapid for the syn relative to the anti conformer. Quenching by secondary and tertiary amines results in the regioselective formation of N-H and α-C-H adducts respectively. The quantum yields of photoisomerization and photoaddition were determined for a mixture of the conformers, but were not separated into values for the individual conformers. The spectroscopy and photochemistry of ethyl-1-naphthylacrylate, which exists as a single conformer, were also investigated.