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Synthesis of Photochromic Diarylethenes Bearing a Benzothiophene /Benzofuran Moieties and Investigation of Their Optoelectronic Properties

Author: YanPeiJian
Tutor: PuShouZhi
School: Jiangxi Science and Technology Normal University
Course: Applied Chemistry
Keywords: diarylethene photochromism thermal stability fatigue resistance substitution effect
CLC: O621.3
Type: Master's thesis
Year: 2011
Downloads: 53
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Abstract


Due to the potential applications to many fields such as optical memories, optical switches, and full-displays, organic photochromic materials as functional materials have been widely focused. Among many known photochromic systems, diarylethenes are the most promising candidates for optoelectronic devices because of their excellent thermal stability of both isomers and good fatigue resistance. Currently, developed series novel diarylethenes as well as investigated the relationship of their molecular structure and properties are both fundamental research and hotspots.In this thesis, two kinds of new unsymmetrical diarylethenes with different aryl moieties were synthesized and their optoelectronic properties were investigated systematically, especially in exploring the effects of substitution. The main research results are shown as follow:1. Twenty new unsymmetrical diarylethenes were synthesized and their structures were identified by NMR, IR and elemental analysis. Sixteen diarylethene crystals were prepared, and their structures were determined by single-crystal X-ray diffraction analysis.2. The photochromism properties of these diarylethene derivatives were investigated in some different medial, such as solution, PMMA films and crystalline state. Also, we have researched the acidchromism properties of diarylethenes DT-1820 in acetonitrile. The results revealed that the substituent and the substituent position had a significant effect on the properties of these diarylethene compounds. In the crystalline phase, although diarylethenes compounds DT-1, DT-11 packed with an anti-parallel conformation and the distances between the two reactive carbon atoms were both less than 4.2 （?）, they showed no photochromism. However, the diarylethenes DT-9 and DT-12 showed good photochromism in their respective crystalline phase, which were the first examples of photochromic diarylethenes crystals bearing benzene moieties. 3. All diarylethenes were thermal stability in hexane at room temperature. But at 80oC, the closed-ring isomers of diarylethenes DT-1 and DT-9 bearing strong electron-donating groups were thermal instability. The fatigue resistance of diarylethenes DT-1320 was much stronger than other compounds, especially in PMMA amorphous film. After 200 repeated cycles, diarylethenes DT-1320 still showed good photochromism with the absorbance maintained above 80% basically.4. The fluorescence spectra of diarylehtenes have been investigated both in hexane and in PMMA amorphous film. The results illustrated that the open-ring isomers of diarylethenes could exhibit relatively strong fluorescence, but the closed-ring isomers showed almost no fluorescence. The relative fluorescence intensity increased dramatically with the increase in the concentration. But when the concentration increased to 1.0×10-3mol/L, the fluorescence intensity decreased remarkably. Furthermore, diarylethenes DT-58 and DT-1420 exhibited notable fluorescence photoswitches both in hexane solution and in PMMA film. In addition, in the diarylethene system bearing benzothiophene and benzene moieties, the electron-donating substituent could be effective to decrease the efficiency of the fluorescence and decrease the emission peak. And in the diarylethene system bearing benzofuran moiety, the electron-withdrawing cyano group improved the fluorescence quantum yields and shifted the emission peak to longer wavelength.5. Cyclic voltammetry tests indicated that the different substituents had a significant effect on the electrochemical behaviour of these diarylethenes. The oxidation potential onsets of the closed-ring isomers were clearly lower than those of the open-ring isomers.

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