Structural Engineering of Photoisomerizable Covalent Organic Frameworks: Design Principles and Functional Applications.

Photoisomerizationa reversible molecular transformation triggered by lighthas emerged as a powerful tool for developing smart responsive materials, offering spatiotemporal control and non-invasive operation. Despite these advantages, conventional photoisomeric systems face fundamental limitations, including inefficient isomerization kinetics, structural rigidity, and poor cyclability, which hinder their practical implementation. Covalent organic frameworks (COFs) present an ideal platform to overcome these challenges, combining precisely engineered pore architectures, tunable topologies, and exceptional stability with the capacity to integrate diverse photoresponsive units. This review systematically examines the latest advances in photoisomerizable COFs, focusing on three critical dimensions: (1) rational design strategies for optimizing photoswitchable building blocks and framework geometries, (2) innovative synthetic methodologies enabling precise functionalization, and (3) mechanistic insights into light-driven structural transformations within confined nanopores. We further highlight their transformative potential in advanced applications such as selective gas separation, environmental remediation, smart membranes, and photocatalytic systems. By elucidating structure-property relationships and current technical barriers, this work provides a roadmap for designing next-generation photoresponsive materials with enhanced performance, durability, and functionality, bridging the gap between fundamental research and real-world applications.