Activation and Deactivation of Chirality Transfer in the Superbundles of Sequence‐defined Stereoisomers

Abstract

Discrete oligomers can be used to precisely evaluate the structure‐property relationship and enable unique chiroptical activities, however, the role of stereochemical sequences in chirality transfer is still unclear. Herein, we report the successful synthesis of a series of sequence‐defined chiral azobenzene (Azo) oligomers via iterative stepwise chain growth strategy, and the discovery of controllable activation and deactivation of chirality transfer. Sequence‐defined stereoisomers with one single chiral (L or D) stereocenter at the α‐position, ω‐position and middle‐ (m‐) position have completely different self‐assembly dynamics and chirality transfer mechanisms. ω‐positional stereocenter can effectively command all Azo building blocks to adopt a tilted π‐π stacking along the helical superbundles, exhibiting the activation of chirality transfer. However, discrete oligomers with the stereocenter at other positions can only self‐assemble into non‐helical nanowires, accompanied by the deactivation of chirality transfer. Kinetic experiments as well as chemical simulations indicate that the cooperative supramolecular interaction, including the π‐π interaction between repeated Azo units, the intermolecular hydrogen bonding and steric hindrance, are intrinsic driving forces for these differentiations. This study has shed light on the unique self‐assembled kinetics in stereosequential oligomers and the mechanism of chirality induction at hierarchical levels.