σ-p Hyperconjugation-Enabled Covalent Organic Frameworks for Programmable Cascaded Optical Modulation.

Abstract

σ-p hyperconjugation is identified as an effective molecular lever for regulating the excited-state behavior and donor characteristics of covalent organic frameworks (COFs). Activation of σ-p hyperconjugation amplifies the fluorescence quantum yield of COFs by up to 167-fold, accompanied by a pronounced redistribution of excited-state charge density. This atomic-level electronic regulation enables programmable control over both the direction and magnitude of interfacial charge transfer in COF-OMe/Eu@UiO-66-(COOH)₂ heterojunctions, giving rise to cascaded excitation-emission coupling and excitation-dependent multicolor outputs. Perturbation of the hyperconjugation-enhanced interface by hormone binding modulates the interfacial charge-transfer landscape, resulting in distinct optical fingerprints that reflect subtle molecular stimuli. When incorporated into electrospun polyacrylonitrile membranes, these programmable optical responses are preserved in a flexible, antibacterial, and machine-learning-readable format, enabling rapid visual readout, quantitative concentration discrimination, and efficient solid-phase extraction. Conceptually inspired by the multilayered optical modulation of chameleon skin, this work establishes σ-p hyperconjugation as a general design principle for constructing electronically adaptive COF-MOF heterostructures capable of transducing molecular perturbations into tunable optical signals.