Radial growth of twist-stacked covalent organic framework nanofibers

Engineering symmetry breaking is a fertile ground to develop innovative materials with fascinating properties. Herein, we introduce crystallographically incompatible rotation element into two-dimensional polymers and construct twist-stacked covalent organic framework nanofibers (abbreviated as t-COFs). These t-COFs are derived from polymerization between 2,4,6-triformylphloroglucinol and diamines modulated by monodentate alkylamine. Comprehensive electron microscopy analysis reveals their well-defined fibrous morphology and twist-stacking details. The time-dependent growth process study discloses a new radial growth pattern, which enables t-COFs to inherit twist-stacking from hexagonal macrocycle nanotube intermediate. Intriguingly, the twist-stacking mode is found to be intrinsic when using amine modulator, and enantiomeric bias towards one stacking direction can be achieved using chiral amine. Disrupting the inversion symmetry, the consecutive regular rotation of COF layers endows COF nanofibers with structural chirality and large chiroptical response.