σ‐π Hyperconjugation as a Design Strategy for High‐Performance Fluorescent Covalent Organic Frameworks

Abstract Realizing efficient solid‐state fluorescence in covalent organic frameworks (COFs) represents a persistent and fundamental challenge in materials science, hindering their application in next‐generation optoelectronics. Herein, a transformative strategy leveraging σ‐π hyperconjugation is introduced to enhance the fluorescence properties of COFs. The incorporation of a methyl group into a pyrene‐based COF monomer yields an unprecedented fluorescence quantum yield increase of more than 100‐fold, accompanied by significantly enhanced optoelectronic performance. This enhancement arises from σ‐π hyperconjugation, which redistributes electron density, converting pyrene from an electron donor to an electron acceptor and facilitating efficient electronic transitions. Additionally, a COF‐based fluorescent acoustic sensor, fabricated via electrospinning, demonstrates real‐time speech pattern recognition when integrated with machine learning algorithms, showcasing potential in language‐assistive technologies. This study pioneers the exploration of hyperconjugation in COFs, offering a new paradigm for the precise modulation of optoelectronic properties and bridging fundamental research with real‐world applications.