Synthesis And Photochromic Properties Of Nitrogen-containing Heterocyclic Thiosemicarbazone

Bistable molecules with stimuli-switchable characteristics are of considerable practical and fundamental interests, such as application in molecular switches, data storage media, logic gates, and so on. Typical bistable molecules are known as photochromic compounds. So far, the method of the synthesis of photochromic compound with excellent performance has been focused on modification of existing photochromic compounds. However, only develop new photochromic system and design new photochromic compounds can promote the development of this field.In this paper, we have synthesized a series of nitrogen-containing heterocyclic thiosemicarbazone compounds. The composition and structures of these photochromic compounds were characterized by 1H NMR, elemental analyses and X-ray single crystal diffraction and the property of photochromism were study.Meanwhile the relationship between structures and properties has been discussed. It has provided the scientific basis and theoretical foundation for the research, and the primary coverage as following.1. Three new compounds pyrazolone 4-phenylsemicarbazones have been synthesized through different substituent pyrazolone and 4-phenyl thiosemicarbazide condensation. For the first time found that the pyrazolone4-phenylsemicarbazones have photochromic properties. The composition and structures of these photochromic compounds were characterized by 1H NMR,elemental analyses and X-ray single crystal diffraction. The photochromism were signed by UV-Vis spectrum. Meanwhile the influences for the structures of electron–withdrawing substituting to the photochromism were discussed. Based on the crystal structure and solid IR spectra, we proposed the photochromic mechanism:proton transfer from enol–form to keto–form in the solid state.2. The compound of pyrrole-2-formaldehyde 4-phenylsemicarbazones(BL2C-PTSC) has been synthesized with three different experimental such as usingchloroform as solvent with heating circumfluence and ethanol as solvent with heating circumfluence or microwave irradiation. Based on the solid IR spectra, 1H NMR,crystal structure, solid-state UV-vis absorption spectra and theoretical calculation, we proposed that under the same experimental conditions, the compounds with different molecular structure were obtained by using different solvents. The photochromic properties have been studied by solid-state UV-vis absorption spectra. In solid state,the compound which was synthesized with microwave irradiation exhibit good reversible photochromic properties, then the photochromic properties of this compound in solution have been studied by solid-state UV-vis absorption spectra.Based on the 1H NMR, we proposed the photochromic mechanism: cis-trans isomerization about carbon-nitrogen double bond. And a new photoactive BL2C-PTSC / poloxamer composite materials was prepared as the same properties with the compound in solution.3. Eight new indole-3-carboxaldehyde thiosemicarbazones compounds have been synthesized through molecular modification and characterized by 1H NMR spectra and X-ray single crystal diffraction. In addition, the photochromic properties have been studied by solid-state time-dependent UV-vis absorption spectra and fluorescence spectra. Based on the crystal structure, solid IR spectra and theoretical calculation, we proposed the photochromic mechanism: intermolecular double-proton transfer in the solid state.