Synthesis, Structure and Properties of Two Photochromic Compounds Containing A Pyrazolone-ring

Two photochromic compounds with the pyrazolone-ring as the photochromic functional structure, 2-(1'-phenyl-3'-methyl-4'-benzoformyl-pyrazolone-5')-thiosemicarbazone(PMBP-TSC) and 2-(1'-phenyl-3'-methyl-4'-benzoformyl-pyrazolone-5')-S-methylthiosemicarbazone(PMBP-MTSC), were synthesized and characterized by elemental analysis, MS, IR spectra, NMR spectra. The crystal structure of the photocolored product of PMBP-TSC was determined by single crystal XRD analysis. The results show that the photochromic phenomenon is due to the photoisomerization from enol form to keto form. Their photochromic properties were studied by powder-UV reflectance spectra under the irradiation of 200-380 nm light. The first-order rate constants of the photocoloring reaction were found to be 7.80×10-3 s-1 for compound 1A and 1.03×10-3 s-1 for compound 2A.