Synthesis, properties, and mechanism of two novel photoisomerization pyrazolones in the solid state

Two novel photoisomerization compounds derived from pyrazolones have been synthesized successfully. The photoisomerization properties of materials have been carefully investigated by measuring the UV–vis absorption and fluorescence spectra of the materials. It was found for the first time among the derivatives of pyrazolones that the compounds change their color from yellow to brown with an efficiency of more than 95% of modulating the fluorescence behaviors, after irradiated with visible light. The unique fluorescent changes of the two compounds between their “on” and “off” states in the solid state indicate that the materials could be used as building blocks to construct novel optical switches. The mechanism of the photoisomerization was further studied with FT-IR, XPS and X-ray single crystal diffraction. The photoreaction resulted from isomerization between the enol and keto forms of the materials is accompanied by intra- and inter-molecular proton transfer.