Dynamic Water Bonding on Clusters Enables Ultrafast Humidity Response and Recovery

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 PhQPCu₃I₃ featuring a semi-exposed Cu₃I₃ crown. Compared to ligand encapsulated Cu₄I₄ clusters, low coordination, short distance and same orientation of iodine atoms in PhQPCu₃I₃ lead to a rapid and reversible "H₂O + 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%, PhQPCu₃I₃ 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, PhQPCu₃I₃ 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.