Luminescent Covalent-Organic Frameworks: Design Strategies, Photophysical Mechanisms, and Applications

Luminescent covalent-organic frameworks (COFs), exquisitely built from structurally defined organic molecular unit interconnected through covalent bonds, have become transformative materials in optoelectronic technologies. Through the judicious selection of molecular building blocks and the deliberate design of topological frameworks, the construction of COFs with outstanding luminescent performance becomes possible. This review begins by illuminating crystal engineering approaches that enable precise modulation of emissive properties in molecular constituents, accompanied by a comprehensive survey of the building blocks that have driven recent breakthroughs in luminescent COFs. It further delves into the fundamental photophysical mechanisms underpinning COF-based emission, demonstrating how fluorescence and phosphorescence can be finely tuned through a series of strategies including the hydrogen isotope effect, aggregation-induced emission, excited-state intramolecular proton transfer, crystal preparation, heavy atom effects, host-guest regulation, donor-acceptor systems, and so on. Additionally, luminescent COFs' principal uses are accentuated, spanning white-light-emitting devices, sensing technologies, drug delivery systems, and nonlinear optics. Finally, the critique offers an anticipatory viewpoint regarding prospective possibilities and obstacles, offering thoughtful reflections on material design, mechanistic understanding, and the broader application potential of luminescent COFs.