Multi-Stimuli Chromic Responses (Light/Electro/Amino-) in Zn/Cd-Extended Viologen Materials toward Information Encryption

Abstract

Significant progress has been made in the research of stimuli-responsive materials in recent years. Among these, viologen-based functional coordination compounds have shown remarkable prominence due to the excellent redox properties of viologens. Herein, a π-conjugation extension strategy was employed by introducing a diphenyl sulfone group between the viologen pyridine units to enhance its performance. Using this extended viologen 4,4'-(sulfonylbis(4,1-phenylene))bis(1-(4-carboxybenzyl)pyridin-1-ium) chloride [(H2L)•2Cl] as a ligand, with d10 configured metals (Zn2+/Cd2+) as central atoms and terephthalic acid (PTA) as an auxiliary ligand, two novel crystalline materials {[Zn(L)(PTA)(H2O)]•4H2O}n (1) and {[Cd(L)(PTA)0.5(FA)]•6H2O}n (2) were successfully constructed. Both materials exhibit rapid and reversible photochromic behavior. The mechanism for this photochromic behavior is attributed to electron transfer from the carboxylate groups and water molecules to the viologen pyridine nitrogen atoms. Furthermore, the materials possess excellent electrochromic properties, showing good reversibility in air, and also show a specific color change response toward amine vapors. This work aims to develop stimuli-responsive materials that combine structural stability with functional diversity, thereby enriching the range of materials available in this field.