| Ground state conformational control of the photochemistry and photophysics of trans- and cis-1-(2-naphthyl)-2-phenylethene, t- and c-NPE, was investigated. The absorption spectra of the two conformers of each NPE isomer differ. Since the conformers do not equilibrate in the excited state, both isomers exhibit strong excitation wavelength dependent behavior.; The quantum yields of cis-trans photoisomerization, cyclization and fluorescence for c-NPE, and the fluorescence quantum yields of t-NPE were shown to depend on solvent polarizability and on the excitation wavelength. Dramatic demonstration of the adherence of c-NPE to Havinga's NEER principle (nonequilibrating excited state rotamers) is provided by its fluorescence spectrum in methylcyclohexane which includes fluorescence from the extended t-NPE conformer, t-NPE B. The adiabatic c-NPEB* → t-NPEB* isomerization is not observed in benzene. No adiabatic c-NPEA* isomerization was detected in the fluorescence spectra in either benzene or methylcyclohexane. c-NPE B* does not fluoresce in benzene.; The photochemical interconversions of previtamin D and of c-NPE are shown to be analogous. The wavelength dependence of the quantum yields of cyclization and isomerization of previtamin D and of c-NPE are both explained on the basis of the NEER principle. Alternative explanations proposed for previtamin D by Dauben, involving upper singlet excited state, and by Fubeta, involving hot vibronic excited states, are not needed to account for the excitation wavelength dependence of the quantum yields.; The geometries of the two conformers of each NPE isomer as well as the products of cyclization from the two cis isomers were optimized and the ground state energies were calculated at the B3LYP/6-311G(d,p) and HF/6-311G(d,p) levels of theory. These results were combined with spectroscopic data to propose energy diagrams for the ground and first singlet excited state.; Numerical data methods, Principal Component Analysis, PCA, Singular Value Decomposition, SVD, were applied during the spectral analysis. New analytical procedures were developed and evaluated for the purposes of the numerical data analysis. |
