Fabrication of heteropolyoxometalate-based photochromic inorganic-organic nanocomposites

A series of photochromic sol-el films are prepared through entrapping tungs ten heteropolyoxometallates (PW12O403-, SiW12O404-) and molybdenum heteropo lyoxometallate (PMo12O403-) into a kind of inorganic-organic matrix cohydro lyzed from tetraethylorthosilicate and 3-aminopropyltriethoxysilane. The fi lms show reversible photochromicity. Irradiated with ultraviolet light, the transparent films change from colorless to blue. Then, bleaching occurs wh en the films area in contact with air or O-2 in the dark. The Keggin-type p olyanions interact with R-NH3+ cations strongly, and thus disperse uniforml y in the sol-gel matrix, as proved by Fourier transform infrared spectra an d x-ray diffraction. The molybdenum heteropolyoxometallate sol-gel film has higher photochromic efficiency and much slower bleaching than its counterp arts of tungsten heteropolyoxometallate. A charge-transfer model which is s upported by electron spin resonance and related literature [T. Yamase, Chem . Rev. 98, 307, (1998)] is put forth to explain the above experimental resu lts.