Enabling Racemization of Axially Chiral Subphthalocyanine-Tetracyanobutadiene-Aniline Enantiomers by Triplet State Photogeneration.

In recent years, several tetracyanobuta-1,3-diene (TCBD) conjugates have been prepared by linking the tetracyano unit to various electroactive moieties. These push-pull conjugates, besides showing interesting physicochemical properties, are axially chiral, a feature arising from the restricted rotation around the central bond of the butadiene. Yet, only in a few cases, separation and isolation of the enantiomers have been successfully achieved, owing to the configurational lability of the corresponding enantiopure species. Herein, we report the first example of photo- and electroactive TCBD-based derivatives showing unprecedented configurational stability and a peculiar light-triggered enantiomer conversion mechanism enabled by triple-state photogeneration. These systems represent a nice addition to the fast-increasing arsenal of artificial, light-controllable molecular switches.