Zinc tungstate encapsulated into a scarce Zn()-viologen framework with photochromic, electrochromic and chemochromic properties

• Published in: Dalton transactions : an international journal of inorganic chemistry 2024-03, Vol.53 (11), p.5192-521
• Main Authors: Huang, Li, Li, Xiao-Nan, Shen, Yuan, Song, Run-Hong, Cui, Wen-Bo, Zhang, Hong
• Format: Article
• Language: English
• Subjects: Amines; Anions; Cations; Chemical sensors; Clusters; Dichlorides; Electrochromic cells; Electrochromism; Electron transfer; Encapsulation; Linkages; Oxygen; Photochromism; Photoluminescence; Polyoxometallates; Smart materials; Stimuli; Windows (apertures); Zinc tungstates
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d3dt03647b

Smart chromic materials reacting to physicochemical stimuli are widely applied in optical switches, smart windows, and chemical sensors. Currently, most materials only respond to a single stimulus, but those that respond to multiple external stimuli are still in the minority. Herein, we report a novel porous zinc tungstate@metaloxoviologen framework [Zn 3 (Bcbpy) 6 (H 2 O) 2 ]-[ZnW 12 O 40 ]·6H 2 O ( ZnW 12 @MV , H 2 BcbpyCl 2 = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridinium dichloride), which shows multiple stimulus-responsive properties due to a combination of different functional motifs, namely, viologen electron acceptors, luminescent zinc-oxygen-clusters, porous cationic frameworks, and ZnW 12 O 40 6− electron donors. Generally, the large-sized polyoxometalate (POM) anions serving as structure-directing agents can easily direct the formation of the oligomeric metaloxoviologen cations, mainly because POMs may break down some linkages leaving larger spaces for themselves. The large ZnW 12 O 40 6− anions in ZnW 12 @MV are encapsulated into three-dimensional (3D) metaloxoviologen frameworks built up from the linkages of trinuclear zinc-oxygen clusters and Bcbpy viologens, which offer the first example of a 3D metaloxoviologen framework induced by large-sized POM anions. ZnW 12 @MV shows a reversible chromic response to X-ray/UV and electricity via different stimulus-induced electron transfers between electron-rich POM anions and electron-deficient metaloxoviologen frameworks, whereas the coloration changes are ascribed to the formation of radical and mixed-valence colored state ZnW 12 O 40 6− species. The photochromic behavior is accompanied by photoluminescence quenching. The discriminative response to different-sized amines is attributed to the formation of viologen radicals through host-guest electron transfer. These results indicate that the multi-stimulus response ZnW 12 @MV can be applied in electrochromic devices, inkless erasable printing, and the detection of amines. A new type of POM-metaloxoviologen hybrid with a 3D trinuclear Zn( ii )-viologen framework encapsulating POMs exhibits multiple stimulus-responsive behaviors.