title: Quantum chemical investigation of thermal cis-to-trans isomerization of azobenzene derivatives: substituent effects, solvent effects, and comparison to experimental data.
abstract: Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis --> trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis --> trans isomerization of azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push-pull azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined values. Also, trends in the resulting rate constants are correct. Other computed properties such as activation entropies and thus preexponential rate factors are in only moderate agreement with experiment.
authors.affiliation: Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam, Germany.
authors.forename: Jadranka
authors.initials: J
authors.lastname: Dokić
authors.forename: Marcel
authors.initials: M
authors.lastname: Gothe
authors.forename: Jonas
authors.initials: J
authors.lastname: Wirth
authors.forename: Maike V
authors.initials: MV
authors.lastname: Peters
authors.forename: Jutta
authors.initials: J
authors.lastname: Schwarz
authors.forename: Stefan
authors.initials: S
authors.lastname: Hecht
authors.forename: Peter
authors.initials: P
authors.lastname: Saalfrank
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D003198:Computer Simulation; D007536:Isomerism; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D001391:Azo Compounds; D012997:Solvents; C009850:azobenzene