Dynamic Water Bonding on Clusters Enables Ultrafast Humidity Response and Recovery

Abstract Fast response and recovery are crucial for real‐time human‐body related (HBR) humidity monitoring, which faces a formidable challenge, due to the opposite requirements on interaction intensities of sensing materials with water. Herein, we demonstrate the first cluster‐based humidity sensor with PhQPCu 3 I 3 featuring a semi‐exposed Cu 3 I 3 crown. Compared to ligand encapsulated Cu 4 I 4 clusters, low coordination, short distance and same orientation of iodine atoms in PhQPCu 3 I 3 lead to a rapid and reversible “H 2 O + I…I” reaction. Consequently, besides more than doubled sensitivity of 106 and halved hysteresis error of 3.2% in related humidity range of 11%–97%, PhQPCu 3 I 3 endows its devices with ultrashort response and recovery time of 0.54 and 0.45 s comparable to human reaction time (0.5 s). Owing to its record‐low comprehensive reaction time within 1.0 s, PhQPCu 3 I 3 based sensors were used for real‐time respiratory rate monitoring and non‐contact information input. Our results demonstrate the effectiveness of “dynamic synergistic bonding” in combining rapid water adsorption and desorption and superiority of cluster sensors in real‐time HBR applications.