Overcrowded Alkene Photo‐Redox‐Switches Based on Quinolinium/Carbene Building Blocks

Abstract

ABSTRACT The design and characterization of a novel class of overcrowded alkene‐based photo/redox switches are presented. Folded and twisted tetrasubstituted alkenes are prepared in a modular fashion by the combination of quinolinium salts and stable carbenes. The compounds show multi‐stimuli responsive properties: besides electrochemical redox‐switching, which allows C─C bond rotation via a two‐electron redox process, non‐symmetrical compounds enable photochemically driven E / Z ‐switching. The different oxidation states can be isolated and fully characterized including structural changes verified by x‐ray diffraction. Excellent photostability for E / Z ‐switching was observed in selected cases and is supported by UV–vis, NMR, and x‐ray data as well as computations. TD‐DFT calculations accurately predict the absorption properties of the E / Z ‐photo‐switches and the substituent effects governing photo‐stationary states and half‐lifes. While the thermal E / Z ‐back‐switching proceeds via a rather high energy barrier featuring a diradical transition state, electrochemical switching via the radical cation oxidation state allows instantaneous E / Z ‐isomerization, which is catalytic in electrons (electron hole catalysis). The mechanism of the switching process is supported in detail by quantum chemical calculations including nonadiabatic molecular dynamics simulations.