Engineering intralayer anisotropy in covalent organic frameworks

Abstract

Precise control of intralayer anisotropy in two-dimensional covalent organic frameworks (COFs) remains a significant challenge in materials design. We address this through a mixed-linker strategy using 8-connected pyrene and triphenylamine monomers with 4-connected ETTA to form 1D nanoribbons. These ribbons are longitudinally stitched by diamines of programmable lengths, enabling precise in-plane anisotropy tuning. Shortening the linkers from biphenyl to phenyl (T-COF-2 → T-COF-1) induces compressive strain within the π-conjugated backbone, enhancing π-electron delocalization and boosting photogenerated charge carrier mobility by over fourfold. Consequently, T-COF-1 achieves a 93.81% conversion efficiency in visible-light-driven NADH (nicotinamide adenine dinucleotide) oxidation—a 4.26-fold enhancement over T-COF-2—along with a 1.41% apparent quantum yield at 420 nm. Remarkably, T-COF-1 retains substantial activity under 650 nm near-infrared light (14.67% conversion, 0.11% quantum yield), highlighting its potential for photodynamic therapy. This work establishes interchain covalent proximity as a design principle for rationally engineering high-performance COF photocatalysts, with broad implications for solar energy conversion and biomedical applications.