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

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.