Investigation of London Dispersion Interactions with Azobenzene Switches

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The effect of bulky groups has been mainly considered according to their repulsive interactions. Recently, it has been realized, that the attractive part of the van-der-Waals interactions, London dispersion, can be utilized as stabilizing element in molecular and reaction design. Despite the progress made, the nature of these forces are still not fully understood. Especially the experimental evaluation of the strength in terms of dispersion of different groups (dispersion donor groups = DDGs) has only been scarcely addressed. A long disputed issue is the effect of solvation on dispersion. In the past years, we could show that the thermal back reaction of azobenzene from the Z- to the E-isomer is ideally suited to address these questions. It allows positioning two DDGs in close proximity. By examining the isomerization rate, the stability of various DDGs can be assayed based on the Bell-Evans-Polyani relationship. Herein, various DDGs ranging from alkyl to structures relevant in life science, such as peptides, nucleobases, etc. will compared according to their dispersion strength. Furthermore, the influence of different solvents on the dispersion strength of given DDGs will be investigated providing essential guidelines, how to design ideal conditions to make the best use of dispersive interactions. The studies will be completed with collaborative efforts with other groups within the SPP 1807 in the area of catalysis, supramolecular chemistry and structural analysis.