A novel multicolor viologen-derived Zn-organic coordination polymer for environment friendly ink free erasable printing

A series of viologen/POM materials with discoloration properties under the stimulation of X-ray, UV, electricity, and organic amines

At present, viologen-based compounds can undergo reversible chemical/physical changes under external stimuli such as light and electricity. This makes these compounds have potential applications in smart windows, displays, and sensors. In order to obtain such materials, three viologen-POM inorganic-organic hybrid compounds have been successfully synthesized by a hydrothermal method, namely {[Cu2(cybpy)8(α-P2W18O62)2}·18H2O (1), (Hbpy)·(cybpy)·[H4(α-P2W18O62)]}·32H2O (2) and {(Hcybpy)2(β-Mo8O26)}·2H2O (3) (cybpy·Br = 1-cyclobutylmethyl-[4,4']bipyridinyl-1-ium bromide, bpy = 4,4'-bipyridine). Three compounds exhibit good discoloration behaviors under various external stimuli, especially under the stimulation of X-ray, UV, electricity, and organic amines. In addition, in order to promote the compounds in the actual production of more applications, they were doped into the polymer matrix to construct hybrid films, which not only have the same response to external stimulation but also increase the repeatability of the photochromic process. Moreover, 1-3 powder samples in ethanol solution were ultrasonic treated and deposited on filter paper, which can be successfully used in erasable inkless printing.

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

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 [Zn3(Bcbpy)6(H2O)2]-[ZnW12O40]·6H2O (ZnW12@MV, H2BcbpyCl2 = 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 ZnW12O406- 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 ZnW12O406- anions in ZnW12@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. ZnW12@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 ZnW12O406- 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 ZnW12@MV can be applied in electrochromic devices, inkless erasable printing, and the detection of amines.

A series of naphthalenediimide-based metal-organic frameworks: synthesis, photochromism and inkless and erasable printing

Three new three-dimensional metal-organic frameworks were synthesized based on a naphthalenediimide derivative ligand, all of which exhibit photochromic behaviour due to the presence of the naphthalenediimide core. Interestingly, two of them possess significant colour changes under light, excellent stability, and appropriate photochromic lifetimes, thus showing potential for application in inkless and erasable printing media.

Metal-organic framework bearing new viologen ligand for ammonia and Cr2O7 2- sensing

Three anionic metal-organic frameworks (MOFs) {[Zn₃(BTEC)₂(H₂O)(4-BCBPY)]·(H₂O)} _n (1-3) (BTEC^4- = 1,2,4,5-benzenetetracarboxylic acid anion, 4-BCBPY²⁺ = 1,1'-bis(4-cyanobenzyl)-4,4'-bipyridinium dication) were synthesized in the reaction of 1,2,4,5-benzenetetracarboxylic acid with different metal salts such as ZnNO₃, ZnCl₂, and ZnSO₄, under solvothermal conditions in the presence of 1,1'-bis(4-cyanobenzyl)-4,4'-bipyridinium chloride. Single crystal X-ray diffraction analysis shows that compounds 1, 2 and 3 have MOF structures based on binuclear metal building units, which are connected by two protonated BTEC^4- ligands and three zinc ions, and the viologen cation 4-BCBPY²⁺ is located in the channel to achieve charge balance. Compounds 1, 2 and 3 have good photosensitivity, respond to sunlight, UV light and blue ray, and turn blue. The D-A distance and π-π stacking distance of the discolored samples (1P, 2P and 3P) changed. In addition, the three compounds showed visible color changes to ammonia vapor, rapidly changing from white to blue. At the same time, the three compounds exhibited fluorescence quenching to ammonia vapor and Cr₂O₇ ^2-. It is further proved that compounds 1, 2 and 3 are fluorescent sensors with a low detection limit (for Cr₂O₇ ^2-: 10^-5 M) and high sensitivity for ammonia vapor and Cr₂O₇ ^2-. It was found that photochromic behavior, ammonia sensing properties can be tuned by the nature of metal salts.

Two new photochromic supramolecular compositions based on viologen: photocontrolled fluorescence, aniline detection and inkless erasable printing performance

Two multifunctional supramolecular components synthesized by two different viologen ligands and pyromellitic acid.