Novel photochromic thermosetting materials were obtained by integrating polyoxometalate, Keggin type H3PW12O40, and ethylene oxide blocks into a variety of epoxy networks. The dual functions of polyoxometalate as both hardener and photochromophore were studied by differential scanning calorimetry (DSC), infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis) and generalized two-dimentional correlation analysis. Polyoxometalate initiates the cationic polymerization of epoxy resin through dissolving in either polyethylene oxide or epoxy functioned polyethylene oxide. When subjected to UV irradiation for a period of time, the transparent thermosetting resins changes color to blue gradually, and could be bleached in air at various temperature to recover its initial state. From the UV-vis measurement, all the resultant thermosetting materials demonstrated similar photochromic behavior after ultraviolet irradiation showing characteristic d-d transition band and intervalence charge transfer (IVCT) band. The 2D correlation analysis of the photochromic spectra clearly revealed the sequence of electron movement in the framework of PW12 anion, which was extensively studied but not clarified in previous reports.
