Linkage Engineering of Semiconductive Covalent‐Organic Frameworks toward Room‐Temperature Ppb‐Level Selective Ammonia Sensing

Abstract Rational design of molecular architectures is crucial for developing advanced materials such as covalent‐organic frameworks (COFs) with excellent sensing performance. In this work, two isostructural COFs (β‐keto‐AnCOF and imine‐AnCOF) with the same conjugated linkers but distinct linkages are constructed. Although both COFs have porous structure and semiconductor behavior conferred by the identical conjugated backbones, β‐keto‐AnCOF with ─C═O side groups exhibits superior room‐temperature ammonia (NH ₃ ) sensing performance than imine‐AnCOF and even the state‐of‐the‐art dynamic and commercial NH ₃ sensors, i.e., high sensitivity up to 18.94% ppm ⁻¹ , ultralow experimental detection limit of 1 ppb, outstanding selectivity, and remarkable response stability and reproducibility after 180 days. In situ spectroscopy and theoretical calculation reveal that the additional charge transfer between NH ₃ and ─C═O sites in β‐keto‐AnCOF effectively increases the distance between Fermi level and the valence band, enabling highly‐sensitive NH ₃ detection at ppb levels. This work provides novel molecular architectures for next‐generation high‐performance sensors.