Synthesis And Mechanism Of Photochromic Pyrazolones

Organic photochromic materials have attracted considerable attention for their potential applications in high technologies. Pyrazolones are an important class of organic photochromic compounds which exhibit reversible photochromic properties in the solid state when exposed to UV light. An indispensable step for useful applications of photochromic materials is to pass from the solution to the solid state. Therefore, deep studies on this materials will promote further development and application. In this paper, The structure of pyrazolones before and after colored were determined by IR,XPS and X-ray crystallographic analyses. The X-ray structure of the materials reveals the photochromic mechanism of pyrazolone family for the first time. The mechanism of photochromic reaction of pyrazolones was demonstrated on the molecular level. In light of photochromic mechanism of pyrazolones, pyrazolones/polymer photochromic composite films were prepared using water-soluble polymer as matrix material. The mechanism and influence of microstructure of polymer on photochromic reactions in polymer matrix were studied.1. several as-synthesized excellent photochromic properties of compounds through molecular design and structural modification: 1) a new photochromic compound, which exhibited reversible photoisomerization reactions under alternating UV light irradiation and visible light in the solid state, was successfully synthesized by condensing substituted pyrazolone-ring with methylthiosemicarbazone. Upon irradiation with UV light, the materials can change their color from white to yellow, and then return to white again by keeping in visible light. The compound shows similar phenomenon in crystals. 2) we successfully designed two new photochromic compounds, which exhibit highly improved reversible photoisomerization reactions under alternating UV light irradiation and heating in the solid state, produced by condensing phenylsemicarbazide with pyrazolones. The materials exhibit much higher optical sensitivity and fatigue resistance in solid state, compared to those synthesized in our lab previously. 3) two novel photochromic compounds, which can change their color from yellow to brown only under visible light, produced by condensing dimethylthiosemicarbazide with pyrazolones, These photochromic reactions are different from our lab previous studies. The as-synthesized compounds showed similar photochromic phenomenon in crystals. The photochromic properties of pyrazolones were characterized by using UV-Vis and fluorescence spectra, the results show that reversible photochromic compounds can be made by condensing pyrazolone-ring with phenylsemicarbazide.2. The molecular structure of pyrazolones before and after colored was studied by IR and XPS. The results indicate that the enol form transforms to keto form during the photochromic process. The crystal structural changes related to the photochromism of pyrazolones was first observed by using X-ray crystallographic analysis, the length of O–C bond of products becomes shorter than that of colored products, and their photochromic mechanism was further demonstrated on the molecular level. The IR,XPS and X-ray crystallographic analysis results are well consistent with each other, The mechanism of pyrazolones was photo-chemically triggered intra- and intermolecular two proton transfers in crystalline state.3. In order to meet the technical requirements of actual applications, pyrazolones/polymer composite films were prepared and their photochromic reactions was investigated. The effection of microstructure in photochromic reactions and mechanism of the composite films in polymer matrix have been studied. Water-soluble polymer have been proved to be suitable for preparing pyrazolone/polymer composite films. In addition, Based on the difference solubility in good solvents and poor solvents, pyrazolone nanostructures were prepared by solvent diffusion method.