Dynamic tuning of metal–ligand coordination through water molecules to induce multicolor fluorescence variations for humidity monitoring and anti-counterfeiting applications

Abstract

A convenient and rapid relative humidity (RH) detection method using a luminescence response has potential applications in various fields, but it is challenging to obtain luminescent ratiometric RH sensors with wide emission wavelength changes. In this study, a simple and effective strategy has been proposed to construct a luminescent ratiometric RH sensor by incorporating a metal–ligand zinc complex into a polyethylene glycol (PEG) matrix. The resulting luminescent polymer film can convert different RH values into distinctly different fluorescence colors from blue to yellow (450 nm to 547 nm) that can be clearly seen by the naked eye. Moreover, this RH sensor displayed a high sensitivity, good reversibility, and rapid response time. The dynamic tuning of coordination bonds between zinc ions and bipyridine ligands through water molecules was responsible for the emission color changes under different RH values. Furthermore, the luminescent polymer film is used for different applications, including local environmental RH monitoring, human body humidity sensing, and anti-counterfeiting. Overall, this work offers a new method to produce high-performance luminescent ratiometric RH sensors for different photonic applications.