Superhelices with tunable twisting power directed from supramolecular pairing of focal asymmetry in achiral dendron-jacketed block copolymers

IM Lin and CM Chou and MC Li and RH Guo and CK Lee and HJ Li and YW Chiang and YH Lin and YC Lee and CJ Su and US Jeng and WT Chuang, JOURNAL OF MATERIALS CHEMISTRY C, 8, 1923-1932 (2020).

DOI: 10.1039/c9tc06135e

The formation of helical assemblies from achiral supramacromolecules has been a highly mysterious process, but is of interest for the generation of a variety of structures and properties. Herein, novel hierarchical superhelices are developed from self-assembly of achiral dendron- jacketed block copolymers (DJBCPs). The presence of focal asymmetry in both the stereochemistry of the dendrons (donors) and interactive binding sites of the copolymer chains (acceptors) plays a pivotal role in generating a spontaneous symmetry breaking through tailored donor- acceptor matching via hydrogen bonding. The focal asymmetry, on a scale of several nanometers, propagates to helical twists of the achiral DJBCP hierarchical assemblies over hundreds of nanometers, such that the primary molecular asymmetry sequentially triggers a secondary helical conformation of the dendron-jacketed blocks, then tertiary supramolecular helical assemblies and eventually quaternary superhelices. The helical twisting power of the superhelices is tunable using the dendron grafting ratio, indicating that the magnitude of helical twisting can be quantitatively adjusted from local to entire structures.

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