Induction and modulation of supramolecular chirality in side-chain azobenzene polymers through the covalent chiral domino effect

Induction, transfer, and modulation of intriguing supramolecular chirality were achieved in a chiral domino-type polymer system using a chiral alpha-end azobenzene (Azo) moiety as one chiral terminus and achiral Azo repeating units as building blocks. The Azo polymers prepared by atom transfer radical polymerization were imparted with well-controlled chain lengths and a chiral moiety at a well-defined position. One chiral terminus can effectively dictate the helical orientation of the achiral Azo stacks in the aggregation state. The spacer length between the chiral residue and the achiral repeating units dominates the preferred handedness of the side-chain Azo stacks. For instance, the R-configuration moiety with a short alkyl chain (with 0, 2, and 3 carbons) induces right-handed supramolecular chirality, whereas those with long alkyl chains (with 4, 5, and 6 carbons) induce the opposite helical orientation of the Azo units. Moreover, the chiral regulation of polymer aggregates is successfully achieved using the unique photoisomerization transition of the Azo chromophore and the heat-assisted reassembly approach. Chiral induction and chiral-to-achiral communication are further verified via theoretical simulations.