Four POM-Viologen Color-Changing Materials with Fast Color Response under Various External Stimuli

Abstract

Four kinds of polyoxometalate (POM)-viologen compounds were synthesized by hydrothermal method, namely (1−cby. These four POM-viologen compounds exhibit one-dimensional supramolecular network structures. Especially, compound 3 contains a rare sandwich POM subunit {Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 } 10− . These four compounds can be used as color-changing materials, and they all exhibit noticeable color changes upon exposure to light, heat, and electricity. The discoloration mechanism involves viologen derivatives with electrondeficient properties accepting electrons from POM with electron-rich properties under external stimulation, leading to the formation of viologen free radicals. Among them, compounds 1 and 2 also have good properties for ink-free erasable printing, double anticounterfeiting, and ultraviolet detector because of their rapid color response to ultraviolet (UV) light. In addition, compounds 1−4 also show different color changes in the detection of volatile amines.

Four Chromic Compounds Constructed from Keggin Polyoxometalates and Viologens with Applications in Ultraviolet, Metal Ion Detection, and Ink-Free Printing

“…We made the compounds into mixed matrix films of poly­(methyl methacrylate) (PMMA). The powder of 1 – 4 and PMMA were dissolved in dichloromethane (DCM), then evenly smeared on a 2 × 2 cm glass sheet, and dried at room temperature to obtain mixed matrix films with uniform texture . As shown in Figure a-b, PMMA- 1 and PMMA- 2 are initially green, and after being irradiated with an ultraviolet lamp for 3 min, their colors deepen and become dark green and close to black.…”