A Multistimuli-Responsive Chromic Magnesium-Pyridinium Complex for Trace Water Detection, Switchable Photocurrent and Advanced Anti-Counterfeiting.

Abstract

The integration of organic stimuli-responsive groups with electrochemically active metal ions offers a promising strategy for developing novel high-sensitivity photodetectors and other multifunctional materials. Herein, a new magnesium-based pyridinium complex, [Mg(cbby)(H₂O)₅]•DMF (1), was successfully synthesized and comprehensively characterized. Complex 1 exhibits intriguing photochromic and thermochromic behaviors, transitioning from colorless to light black under UV light (365 nm) and to light yellow upon heating (150 °C). Remarkably, the thermally treated phase (1T) demonstrates a significantly accelerated photoresponse, with its photochromic rate constant being 1.68 times faster than that of the pristine sample, attributed to a thermally modified, more efficient electron-transfer pathway. Furthermore, complex 1 demonstrates pronounced photoelectrochemical activity with a high on/off current ratio of 35 under xenon lamp irradiation, underscoring its potential in light-harvesting. The complex 1 also functions as a highly sensitive and selective fluorescent sensor for detecting trace water in organic solvents (MeCN, DMF) with low detection limits (~0.03% v/v). Leveraging its reversible optical switching and tunable fluorescence, proof-of-concept applications in multi-level anti-counterfeiting, rewritable media, and information encryption are successfully demonstrated. This work highlights the great potential of synergistically combining the unique properties of magnesium and photoresponsive pyridinium ligands to create advanced smart materials.