title: Influence of Bridgehead Substitution and Ring Annelation on the Photophysical Properties of Polycyclic DBO-Type Azoalkanes.
abstract: The photophysical data for the polycyclic, bridgehead-substituted derivatives 1-10 of the photoreluctant diazabicyclo[2.2.2]oct-2-ene (DBO) are presented. Substitution on the bridgehead positions with radical-stabilizing substituents enhances the photoreactivity (Phi(r)) and decreases the fluorescence quantum yields (Phi(f)) and lifetimes (tau) compared to the parent DBO. The annelated rings have no influence on the photoreactivity, except when steric interactions with an alpha substituent hinder the optimal radical-stabilizing conformation. The fused rings and some of the bridgehead substituents reduce the solvent-induced quenching of the singlet-excited azo chromophore by steric shielding of the azo group and, thus, increase the fluorescence quantum yields and lifetimes.
authors.affiliation: Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany, and Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany.
authors.forename: Waldemar
authors.initials: W
authors.lastname: Adam
authors.forename: Achim
authors.initials: A
authors.lastname: Nikolaus
authors.forename: Jürgen
authors.initials: J
authors.lastname: Sauer