Synthesis And Photochromic Properties Of 4-Heterocyclic /Substituted Benzoyl Pyrazolones In The Solid State

Organic photochromic compounds have attracted considerable interest because of their potential applications in optical storage media, molecular switching devices, molecular sensors and non-linear optical devices,etc. Pyrazolones, which exhibit reversible photochromic properties in the solid state, belong to a novel class of organic photochromic compounds. An indispensable step for applications of photochromic materials is to pass from the solution to the solid state. Therefore, studies on these materials will promote further development and application. On the basis of previous research, several series of photochromic compounds have been synthesized by the incorporation of heterocyclic and strong electron-withdrawing substituents on phenyl at the 4-position of pyrazolone-ring. The photochromic mechanism of these pyrazolones was analyzed and presumed by studying the photochromic properties and crystal strutures of the photochromic compounds. The relation between structures and properties has been obtained.In the first chapter, eight new compounds (1,3-diphenyl-4-thiophenoyl /furoyl-5-pyrazolone thiosemicarbazones and phenylsemicarbazones) have been synthesized. The composition and structures of these photochromic compounds were characterized by IR, ~1H NMR, MS spectra and X-ray single crystal diffraction. The photochromic properties and photochemical kinetics have been studied by solid-state UV-vis absorption spectra and fluorescence emission spectra under irradiation of 365 nm light. 1,3-diphenyl-4-thiophenyl-5-hydroxypyrazole 4-phenylsemicarbazone (DP2THP-PSC) shows good reversible photochromic properties. Based on the crystal structures, IR spectra and theoretical calculation, we proposed the photochromic mechanism: the intermolecular proton transfer and intermolecular double proton transfer from enol-form to keto-form in the solid state.In the second chapter, twenty new 4-acyl pyrazolone thiosemicarbazones and phenylsemicarbazones have been synthesized. The composition and structures of these photochromic compounds were characterized by IR, 1H NMR, MS spectra and X-ray single crystal diffraction. The photochromic properties and photochemical kinetics have been studied by solid-state UV-vis absorption spectra and fluorescence emission spectra under the irradiation of 365 nm light. Meanwhile, we have researched the thermal bleaching reactivity of photochromic compounds at different temperatures. In solid state, seven of them, especially 1,3-diphenyl-4- benzal/4-nitrobenzal/3-cyanobenzal/4-fluoro-3-trifluoromethylbenzal-5-hydroxypyrazole 4-phenylsemicarbazones (DPBP-PSC, DP4NO2BP-PSC, DP3CyBP-PSC, DP4F3TFBP-PSC) show good reversible photochromic properties and highly fatigue resistant, which have potential application in light-heat controlled switches and fluorescent switches.