Crystal structures and photoisomerization behaviors of five novel pyrazolone derivatives containing furoyl group

Five novel pyrazolone derivatives containing a furoyl group, 1-phenyl-3-furoyl-4-(4-chlorobenzal)-5-pyrazolone thiosemicarbazone (PF4ClBP-TSC) (1)/methylthiosemicarbazone (PF4ClBP-MTSC) (2)/ethylthiosemicarbazone (PF4ClBP-ETSC) (3), 1-phenyl-3-furoyl-4-(2-chlorobenzal)/(3-chlorobenzal)-5-pyrazolone methylthiosemicarbazone (PF2ClBP-MTSC) (4)/(PF3ClBP-MTSC) (5), have been synthesized and characterized by elemental analysis, IR, 1H NMR spectra, and the molecular structures of 2 and 5 were determined by X-ray single crystal diffraction. Photoisomerization properties have been studied by UV–vis and fluorescence spectra. Based on theoretical calculation and crystal structural analysis, the compounds undergo photoisomerization from the enol form to the keto form through an intermolecular proton transfer upon UV light irradiation. Moreover, the photoisomerization rate decreases with the increase of volume of substituent groups on 4-position of thiosemicarbazide and the steric hindrance of Cl atom on benzal of 4-positon on the pyrazolone ring.