A Novel Photochromism Material Based On Both Pyrimidinium And Polyoxometalate: (C4n2h4-C4n2h3) [Mn(H2o)(6)](0.5){Siw12o40}(0.5)Center Dot 5h(2)O

We used the traditional hydro-thermal synthesis method to generate the first photochromic pyrimidinium/polyoxometalate (POM) salt material (C4N2H4-C4N2H3) [Mn(H2O)(6)](0.5){SiW12O40}(0.5)center dot 5H(2)O in situ by using silicotungstic acid and pyrimidine as raw materials. The solid UV diffuse reflectance spectrum of compound 1 was shifted before and after illumination. There was a new broad absorption peak appeared near 370 nm and 624 nm after illumination. With the increase of irradiation time, the peak at 624 nm will shift to 588 nm at which the sample reached light saturation. The color of the sample changed from yellow to grayish green. By studying a series of test: EPR, XPS, UV-Vis, X-ray single crystal diffraction, and density of states (PDOS) calculation, we conclude that the charge transfer mechanism of photochromism may be due to: the generation of pyrimidinium free radicals by light-induced, photochemical reduction of polyoxometalates and the interaction of two aspects. This work enriches the family of photochromism and its theory. (C) 2020 Elsevier B.V. All rights reserved.