Covalent Organic Framework Film with Dynamic C═N─N/C─N═N Conjugated Backbones for Full‐Spectrum UV Shielding

Abstract Covalent organic frameworks (COFs) have garnered significant interest for applications in photocatalysis, energy storage, gas storage/separation, and optoelectronics, yet achieving high‐quality COF films with high UV‐shielding properties still remains a challenge. In this study, transparent COF films are successfully developed and revealed their remarkable UV‐shielding capability: effectively blocking 99.9% of UV light while maintaining over 96% visible transmittance. Under UV irradiation, the COF backbone undergoes structural rearrangements between hydrazo (C═N─N) and azo (C─N═N) configurations, leading to electronic redistributions and enhanced conjugation within the framework. This adaptable COF framework efficiently absorbs and dissipates UV energy through non‐radiative pathways, providing high UV‐blocking properties that dramatically reduce the photooxidation rates of edible oils by up to 16.9‐fold compared to uncoated controls. Additionally, the superior photostability of these COF films makes them promising next‐generation UV‐protective materials for safeguarding sensitive materials and equipment in high‐UV environments, such as high‐altitude, polar, and extraterrestrial settings.