Bifacial ladder polymers enabled by chirality-assisted synthesis that exhibit self-assembly and chirality-induced spin selectivity

Abstract

Abstract The development of structural concepts in polymers has repeatedly enabled advances in molecular organization and emergent functions. Here we introduce “bifacial ladder polymers” —rigid double-stranded backbones bearing two deliberately differentiated molecular faces— realized through a chirality-assisted synthetic strategy. To implement this architecture, we designed a C 2 -chiral 2,8-dibromoindenofluorene monomer bearing two different substituents with syn stereochemistry across the sp 3 -carbon pair, such that only one ladderization geometry is accessible. Polymerization of the enantiopure monomers with a diboronate comonomer under Suzuki-Miyaura conditions affords precursor polymers, which undergo regioselective ladderization to yield well-defined bifacial ladder polymers with fully preserved facial differentiation. The homochiral bifacial ladder polymers display emergent chiroptical behaviour in the solid state: thin films form one-handed supramolecular helices with circular dichroism intensities over 100-fold stronger than those of their monomeric or non-ladder analogues. Strikingly, these films also exhibit robust chirality-induced spin selectivity, with spin-polarization values exceeding ±90% and opposite signs for the two enantiomers, far surpassing their precursor polymers. These results demonstrate that bifacial ladder polymers provide a versatile platform for emergent self-assemblies and functions in organic polymeric materials.