Synthesis, structure and photochromic properties of 4-acyl pyrazolone derivants

A new organic photochromic compound containing pyrazolone-ring photochromic functional unit: 1-phenyl-3-methyl-4-benzoylpyrazole-5-one methyl thioesmicarbazone (1A), and some analogous non-photochromic derivatives were synthesized and characterized by elemental analyses, MS, IR spectra, 1H NMR spectra. The photochromic properties and photochemical kinetics of 1A have been studied by UV reflectance spectra under irradiation of 365 nm light. The crystal structure analyses of photocolored product (1A) show the photochromism is due to the photoisomerization from enol form to keto form. According to the results of structure analyses, an intermolecular proton transfer mechanism of the photochemical process is proposed.