Azobenzene/Acid Binary Systems for Colorimetric Humidity Sensing with Reversibility, High Sensitivity, and Tunable Colors.

Humidity sensors are important for humidity detection in many storage and manufacturing processes. Issues like sensibility, response rate, controllability, and material and preparation process costs need to be taken into consideration for practical applications. Herein, we report an investigation on a series of azobenzene/acid binary systems using easily accessible compounds, whose thin films display reversible and widely tunable color changes in response to humidity stimulation, with high sensitivity, fast color change, and recovery speed. The interesting properties for colorimetric humidity sensing are showcased with potential applications in dynamic art painting, smart windows, and respiration monitoring.