Synthesis And Photochromic Properties Of Schiff-bases Containing Thiophene Ring

Organic photochromic material is a kind of functional materials with the high performance, which has potential applications in optical information storage, molecular switches, optical lenses and optical anti-counterfeiting, etc. So far, a lot of studies have been focused on modification and composite of existing photochromic compounds. However, a driving force for synthesizing of new photochromic compounds and developing new photochromic system, which is also important for promote this area.The paper focuses on the Schiff-base containing a thiophene groups, eleven novel compounds have been synthesized. Their composition, structure and photochemical properties have been characterized and tested. Their photochromic mechanism has been studied. The relationship between structures and properties has been discussed. It has provided the scientific basis and theoretical foundation for the research, development and application of new photochromic materials.In the first chapter, nine new thiophene thiosemicarbazone derivatives have been synthesized. Their composition and structures were characterized by 1H-NMR, 13C-NMR, MS spectra and X-ray single crystal diffraction. The photochemical properties and reaction kinetics have been studied by UV-Vis absorption spectra. The three thiophene thiosemicarbazones have the photochromic properties under the UV light and decoloration upon the visible light in the solid state. The effects of substituted groups at the 5-position of the thiophene on the reaction rate have been discussed. Based on IR spectra and single-crystal structure, the photoisomerizated mechanism in the solid state has been studied. Another six thiophene methylthiosemicarbazones and thiophene phenylthiosemicarbazones have not photochromic properties in the solid state, but they have the fluorescent properties. The mechanism of emitting fluorescence has been explained by the theoretical calculation. A new composite film with the fluorescence thiophene-2-formaldehyde phenylthiosemicarbazone [S2C-PTSC]/polystyrene[PS] was prepared, which has the similar properties with the powders. In addition, thiophene phenylthiosemicarbazones have the photochromic behaviors in the solution. The influence of solvent polarity on their photochromic properties has been investigated.In the second chapter, two novel photochromic benzothiophene-2-formaldehyde phenylsemicarbazone [BS2C-PSC] and benzothiophene-2-keton phenylsemicarbazone [BS2T-PSC] have been synthesized by introducing a benzene ring at the thiophene ring. The composition, structure and properties for the two compounds are researched. We find that the compound of BS2T-PSC exhibits irreversible solid-state photochromic properties. However, the compound BS2C-PSC exhibits reversible photochromic properties, thermally enhanced phenomenon, fluorescent properties and excellent fatigue resistance in the solid state. By the means of IR and single-crystal structure, the photochhromic reaction involved in the isomerisation between the keto form and the enol form via proton transfer by intermolecular hydrogen bonds. And a new photoactive BS2C-PSC/PS composite film was prepared as the same properties with the powders. Therefore, it has a potential candidate for information storage devices and intelligent curtains.