Engineering Covalent Organic Frameworks with Dual Hydrophilic Sites for Subsecond Moisture-Triggered Chromic Switching

Stimuli-responsive smart materials exhibiting rapid and reversible color switching are highly desirable for emerging technologies. In this study, we present a covalent organic framework (PT-COF) constructed from tartaric acid dihydrazide (TAD) and an aldehyde monomer. During the synthesis process, partial in situ decomposition of TAD into hydrazine leads to a distinctive architecture incorporating both hydrazine linkages and residual TAD moieties. This dual-hydrophilic-site design enhances the framework's sensitivity to low-humidity, enabling ultrafast (<1.0 s) and fully reversible moisture-triggered naked-eye color switching of PT-COF between yellow and orange states, accompanied by reversible fluorescence intensity changes, with excellent cycling stability. The material demonstrates promising applications in advanced anticounterfeiting systems and sensitive metabolite detection platforms.