Thermal cis → trans isomerization of azobenzene studied by path sampling and QM MM stochastic dynamics Azobenzene based molecular photoswitches have extensively been applied to biological systems involving photo control of peptides lipids and nucleic acids. The isomerization between the stable trans and the metastable cis state of the azo moieties leads to pronounced changes in shape and other physico chemical properties of the molecules into which they are incorporated. Fast switching can be induced via transitions to excited electronic states and fine tuned by a large number of different substituents at the phenyl rings. But a rational design of tailor made azo groups also requires control of their stability in the dark the half lifetime of the cis isomer. In computational chemistry thermally activated barrier crossing on the ground state Born Oppenheimer surface can efficiently be estimated with Eyring’s transition state theory (TST) approach; the growing complexity of the azo moiety and a rather heterogeneous environment however may render some of the underlying simplifying assumptions problematic. In this dissertation […]