The Functional Regulation Of The Chromogenic Materials Based On Polyoxometalates

Chromogenic materials have attracted much attention due to the applications in large area glazing, information displays, switch devices and optical storage. In this paper, we focus on the preparation of chromogenic materials based on polyoxometalates by layer-by-layer assembly and sol-gel technology.We successfully prepared PVA–POM multilayer films with concurrent photochromism and electrochromism by layer-by-layer self-assembly technique. The composite films can be photochromic and electrochromic from transparent to deep blue by either irradiation with UV light or electrochemical induce, and the photochromism and electrochromism is reversible. The layered nanocomposite films were studied by UV–vis absorption, cyclic voltammetry, chronoamperometry, X-ray photoelectron spectra and atomic force microscopy.We present our exploration in the development of a"dual electrochrome"composite film fabricated from the tungstophosphate (P2W18) and poly(hexyl viologen) (PXV) by a layer-by-layer self-assembly method. The polyanion and polycation species in the multilayer film are both cathodically coloring electrochromic material. The resulting"dual electrochrome"film could display color changes from colorless to blue to violet, achieving a breadth of gray-scale control with adjustable absorption. The high contrast, extended color range, suitable response time, and low operation potential of the electrochromic film should be promising to meet the requirement for developing flexible displays and electrochromic devices. Furthermore, the P2W18/PXV multilayer film modified ITO electrode is pH sensitive, showing a promising multifunctional application.We investigated the effects of film structure on the electrochromic performance of LbL films assembled from inorganic nanoparticle tungstophosphate (P2W18) and weak polyelectrolyte poly(allylamine hydrochloride) (PAH). The influences of film structure on the electrochromic properties of the multilayer were investigated through varying fabrication conditions. Spectroelectrochemical and electrochromic characterizations of assembled films reveal that high concentration of polycation, anion and salt produces thicker and denser film structure, leading to high optical contrast and color efficiency whereas slow response times. Among the three parameters discussed above, salt concentration has the strongest influence on the electrochromic multilayer structure. By adjusting multilayer structure properly, dramatic changes of the optical contrast and response time can be realized.We report the preparation and characterization of a gasochromic silica sensing material containing POM. The fabrication procedure of the gasochromic monolithic pieces is very simple. In addition, the advantage of the POM-SiO2 material is that it is capable of detecting some reducing gases (H₂S and SO₂) at room temperature without any power consumption. The gasochromic material exhibits higher sensitivity to H₂S than to SO₂. The gasochromic response is strongly correlated to the reducing ability of the gas.