Azo-benzene based molecular photoswitches are becoming increasingly important for the development of photoresponsive, soft-matter material systems. In microgels, polymer brushes or DNA, transitions between the (metastable) cis- and the (stable) trans form of azo-containing surfactants permit to conveniently control changes in size and shape of soft nano objects employing optical stimuli [1]. The photochemical properties of the azo-moieties can widely be tuned by introducing various substituents at their phenyl rings. However, not all photochemical properties such as rates of thermal back relaxation can be rationalized by common computational recipes of quantum chemistry, such as Eyring’s transition state theory (TST) [2]. Here we present a characterization of the re-isomerization process of Azo-4F, a member of recently developed class of fluoro-azobenzenes [3], using a transition path sampling approach which can overcome the limitations of TST. We demonstrate how a path sampling simulation is adequately set up for this type of system, and compare ab initio stochastic dynamics in the gas phase to QMMM simulations in various explicit MM solvents such as water, toluene and DMSO. In particular, we analyze in how far the transition state ensemble from path sampling deviates from that inferred by TST. 1. Zakresvkyy, Y.; Titov, E.; Lomadze, N.; Santer, S. 2014. J. Chem. Phys. DOI:10.1063/1.4899281 2. Dokić, J. et al. 2009. J. Phys. Chem. A 113:6763—6773. 3. Knie et al. 2014. Chem. Eur. J. 20:16492—16501.

Elucidating the isomerization relaxation mechanism of fluorinated azobenze using transition path sampling with QM/MM molecular dynamics

251st National Meeting (2016)

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