Two Cd(ii)–viologen coordination polymers with wave-like layered structures used as multi-stimulus-responsive materials

Abstract

Photochromic materials have significant application value in the field of anti-counterfeiting, with viologen-based compounds being particularly noteworthy due to their superior properties. In this study, two cadmium-based coordination polymers Cd (CPB) L1 (1) and [Cd₂(CPB)₂(L2)₂(H₂O)]·2H₂O (2) were synthesized using a solvothermal method (L1 = trimesic acid, L2 = 5-methylisophthalic acid and HCPB·Cl = 1-(4-carboxyphenyl)-4,4′-biphenyl chloride). Both compounds exhibit a two-dimensional wave-like layered structure, with the key difference being that the layers of compound 1 are parallel and cross-hatched, whereas those of compound 2 are parallel without interpenetration. Both compounds display reversible color changes under light or electrical stimulation. The two compounds have similar color change behavior and different fluorescence behavior, with compound 2 showing visible fluorescence. Additionally, we explored the applications of these materials in inkless printing and anti-counterfeiting.