title: Substituent-dependent reactivity in the photodimerization of N-substituted dibenz[b,f]azepines.
abstract: The photoprocesses of a series of N-substituted dibenz[b,f]azepines (iminostilbenes) were studied by absorption and emission spectroscopy, by laser flash photolysis, and by preparative irradiation with NMR analysis. In solutions, 2pi+2pi photodimers of N-cyano and N-acyl dibenzazepines are formed via the triplet state upon acetone- or benzophenone-sensitized energy transfer. T-T absorption spectra were measured and absorption coefficients were determined. The triplet energy transfer is equally efficient for N-alkyl dibenzazepines, which do not dimerize. Excited states of npi* character in the latter cases are discussed to rationalize the different reactivities. In spite of negligible intersystem crossing of 21 dibenzazepine derivatives, photodimers of N-acyl and N-cyano dibenzazepines are formed upon direct excitation in concentrated solutions (0.01-0.1 mol dm(-3)) as well as in the solid state. A selective anti-configuration of the photodimers was found throughout.
authors.affiliation: Institut für Physikalische Chemie, und Elektrochemie der Technischen Universität Dresden, 01062 Dresden, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Querner
authors.forename: Thomas
authors.initials: T
authors.lastname: Wolff
authors.forename: Helmut
authors.initials: H
authors.lastname: Görner