Three zinc-viologen compounds, namely, {[Zn(Mebpy)(Hbtc)Cl]·2H2O}n (1), {[Zn3(Cebpy)2(Hbtc) (H2btc)2 (OH)2]·4H2O}n (2), and {[Zn4(Cebpy)2(IPA)3(OH)2]·2H2O}n (3) (Mebpy = N-methyl-4,4'-bipyridinium, Cebpy = N-carboxyethyl-4,4'-bipyridinium, H3btc = 1,3,5-benzenetricarboxylic acid, and H2IPA = isophthalic acid) have been constructed from aromatic carboxylic acid and viologen-derived ligands. In compound 1, the Hbtc2- ligands bridge Zn2+ cations to form a 1D fence-like chain with the Mebpy+ ligand suspended on the chains. Compound 2 possesses a 2D (4, 4) double-layered grid structure based on linear trinuclear Zn3O2 cluster units. The structure of compound 3 can be described as a 3D open-framework based on tetranuclear Zn4O2 cluster units and helical chains with helical channels. All three compounds display photochromic properties from pale yellow to dark blue after being irradiated by a xenon lamp with different photoresponsive rates. Compounds 2 and 3 can be deposited in paper simply by coating them with a solution of ethanol. The papers can be used as inkless and erasable print media. In addition, the photo-modulated luminescence of these compounds was also investigated.

Three viologen-derived Zn-organic materials: photochromism, photomodulated fluorescence, and inkless and erasable prints

Octahedron-shaped three-shell Ln14-substituted polyoxotungstogermanates encapsulating a W4O15 cluster: luminescence and frequency dependent magnetic properties.

Health concerns as a result of harmful UV-rays drive the development of UV-sensors of different kinds. In this research, a UV-responsive smart textile is produced by inkjet printing and UV-LED curing of a specifically designed photochromic ink on PET fabric. This paper focuses on tuning and characterizing the colour performance of a photochromic dye embedded in a UV-curable ink resin. The influence of industrial fabrication parameters on the crosslinking density of the UV-resin and hence on the colour kinetics is investigated. A lower crosslinking density of the UV-resin increases the kinetic switching speed of the photochromic dye molecules upon isomerization. By introducing an extended kinetic model, which defines rate constants kcolouration, kdecay and kdecolouration, the colour performance of photochromic textiles can be predicted. Fabrication parameters present a flexible and fast alternative to polymer conjugation to control kinetics of photochromic dyes in a resin. In particular, industrial fabrication parameters during printing and curing of the photochromic ink are used to set the colour yield, colouration/decolouration rates and the durability, which are important characteristics towards the development of a UV-sensor for smart textile applications.

/pdf/inkjet-printing-and-uv-led-curing-of-photochromic-dyes-for-1jy1mxaijg.pdf

Inkjet printing and UV-LED curing of photochromic dyes for functional and smart textile applications

A case study of two new covalently bonded polyoxomolybdate–viologen hybrids revealed that “reversible” photochromic properties can be achieved without the need for proton transfer, and the weak electron-withdrawing ability of the coordinated ligand favors photoreduction of Mo(VI) to Mo(V).

“Reversible” photochromism of polyoxomolybdate–viologen hybrids without the need for proton transfer

Ultraviolet light-, temperature- and pH-responsive fluorescent sensors based on cellulose nanocrystals

A novel solar ultraviolet sensitive composite film consisting of fluorescent polyoxometalate and viologen has been readily prepared on solid substrates using a drop casting method, and can be colored and bleached by photoreduction and air oxidation processes. A photoswitchable emission has also been observed with the fluorescence intensity returning to its original value after bleaching of the blue-colored film, which is due to the fluorescence resonance energy transfer (FRET) from the excited states of the Eu(III) ions to colored viologen. The decoloration process takes about 2.5 hours under ambient conditions but can be accelerated by humid air. The absorbance change of the composite film is less than 15% even after 8 cycles of variation between the colorless and blue color states. This is also the reason for the emission intensity change of the composite film. Thus, quick-responsive photochromism and switchable fluorescence are realized by a POM-viologen-based film which shows great potential to realize portable devices for solar ultraviolet detection.

Jia-Qi Sun

Papers

A solar ultraviolet sensor based on fluorescent polyoxometalate and viologen