Studies On The Synthesis, Crystal Structures And Photochemical Properities Of Schiff Base Containing Pyrazolone In The Solid State

Photochromic compounds have been received more and more attention because of their potential application on optical equipment, such as optical memory and molecular on-off. Many photochrimic compounds exemplified photochromic reactivity in solution, but there are not so much reported compounds that show good photochromic properties in the solid state. So it has become all-important to design and synthesize novel pyrazolone derivatives with excellent photochromic properties in the solid state and study the photochromic properties and photochromic mechanism.On the basis of previous work in our laboratory, several novel thiosemicarbazones and semicarbazone compounds containing pyrazolone-ring have been synthesized. The photochromic mechanism was proposed by studing the photochromic properties in the solid state and crystal structure of the photochrimic compounds, the relationship between the structure and photochromic properties have been also analyzed.In the first part, seven new 1,3-diphenyl-5-pyrazol thiosemicarbazones and 1,3-diphenyl-5 -pyrazol semicarbazones have been synthesized and characterized by elemental analyses, IR, 1H NMR spectra and single-crystal XRD. The photochromic properties and photochemical kinetics of the compounds have also been studied by solid-state time-dependent UV-vis absorption spectra and fluorescence emission spectra under irradiation of 365 nm light. Particularly DP3ClBP-PSC and DP4ClBP-PSC exhibit fast velocity in the photochromic reaction and good reversibility and repetition. According to the results of structure analyses, the intermolecular proton transfer mechanism and intra- and intermolecular double-proton transfer mechanism is proposed for photochromism. Furthermore, the crystal structure of DP4ClBP-PSC exists in the stable enol-form. Photochromic mechanism is due to proton transfer through intermolecular hydrogen bond O1–H(1O)···O4′[O(3)-H(3O)···O2′].In the second part, six new 1-phenyl-3-methyl-4-(4-fluoro)benzal-5-pyrazol thiosemicar- bazones and 1-phenyl-3-methyl-4-(4-chloro)benzal-5-pyrazol thiosemicarbazones have been synthesized and characterized by elemental analyses, IR, 1H NMR spectra and single-crystal XRD. The photochromic properties and photochemical kinetics of the compounds have also been studied by solid-state time-dependent UV-vis absorption spectra and fluorescence emission spectra under irradiation of 365 nm light. According to the results of structure analyses, we found that the photochromic mechanism in this part was same as the first part. Particularly, there are two anisomerous molecules in PM4ClBP-ETSC, so the photochromic mechanism is distinct from others.In the third part, four new 4-acyl pyrazolone thiosemicarbazone compounds have been synthesized characterized by elemental analyses, IR, 1H NMR spectra, and the photochromic properties have been studied by solid-state time-dependent UV-vis absorption spectra and fluorescence emission spectra. According to the results of structure analyses of DP2FBP-TSC and PM4NO2BP-TSC, we have supposed the photochromic mechanism of DP2FBP-TSC is intra- and intermolecular double-proton transfer mechanism and analyse the reason of non- photochromism for PM4NO2BP-TSC.