Synthesis And Properties Of New Asymmetric Diarylethenes Bearing A Pyridine Unit

In recent years, organic photochromic materials have acquired a breakthrough. Among the various photochromic systems, diarylethenes are one of the most promising candidates for optoelectronic devices because of their excellent thermal stability and good fatigue resistance, which have been applied in erasable high-density information storage, optical memories, optical switches, and full-displays. Diarylethene compounds have wide applications in the field of removable high density optical data storage, electric molecular switch and photoelectric display technology. At present, design and synthesis of novel diarylethenes as well as investigations of their properties are a new research focus on the functional material fields.In this thesis, twenty-one new asymmetric diarylethenes bearing a pyridine ring were synthesized and their structure were characterized by NMR, IR and elemental analysis. Among these compounds, nine diarylethene crystals were prepared, and three of them are determined by single-crystal X-ray diffraction analysis. investigated The effects of the heterocyclic aryl rings species and the nitrogen atom position in the pyridine group on the optoelectronic properties of these compounds were investigated. The main outcome are described briefly as follow:1. Photochromic properties of these diarylethenes in different medium were studied. Diarylethenes DT-1-22showed good photochromic properties in solution and PMMA amorphous film. Crystals of DT-4-9also showed good photochromic properties, but benzene-pyridine systems DT-10-12showed no photochromic.2. The fatigue resistance of diarylethene compounds DT-4-6and DT-19-22were studied. The fatigue resistance of these diarylethene compounds in PMMA film was better than in hexane solution, respectively. For isoxazole and benzothiophene systems, when their nitrogen atom of pyridine group in ortho-substitution, the fatigue resistance of diarylethene was the best. Especially in PMMA amorphous film, after200repeated cycles, they still showed good photochromism with the absorbance maintained above80%basically. 3. The fluorescence properties of diarylethene compounds DT-1-22both in hexane and in PMMA amorphous film were investigated. These compounds exhibited fluorescence at the open-ring isomer whereas the closed-ring isomer has no or weak fluorescence. Under irradiation of ultraviolet light, fluorescence intensity of diarylethenes decreased with prolonged the irradiation time, but it increased when visible light was used. Such cycle can be repeated many times, thereby fluorescence switch properties are exhibited.4. The effect of acid/base on diarylethene compounds DT-1-21was studied. The absorption maxima of the para-substitution diarylethene compounds (DT-3, DT-6, DT-9, DT-12, DT-18, DT-21) showed an obviously bathochromic shifts after addition of trifluoroacetic acid except for diarylethene compound DT-15. The compound DT-9bearing a pyrrole unit exhibited the largest bathochromic shift value52nm.5. The response and selectivity of Cu2+by diarylethene compounds DT-1-15were studied in acetronitrile solution. The results indicated that only pyrrole system DT-7-9and benzene system DT-10～12could select Cu2+.6. The effect of optoelectronic properties was studied by different five-membered aromatic ring. The results showed that theirs absorption maxima and photoconversion ratios increased with the higher of conjugation degree in closed-ring isomers, but their open-/closed-ring isomers of the molar absorption coefficients decreased. Their fluorescence emission peaks, fluorescent modulation efficiencies and fluorescence quantum yields increased with the higher of conjugation degree in hexane solution. The oxidation potential onset of open-ring isomers decrease with the higher of conjugation degree, but the reduction potential onset of open-ring isomers increased.7. The effect of benzene and pyrimidine on optoelelctronic properties of diarylethene compounds was studied. When nitrogen atom of pyridine ring in the same position, their absorption maximum both of open-and closed-ring isomers, the photoconversion ratio, the fluorescence emission peak and fluorescence quantum yield of benzene systems are bigger than that of pyrimidine systems; however, the cycloreversion reaction quantum yield of benzene systems are smaller than that of pyrimidine system. 8. The effect of naphthalene and benzothiophene on optoelelctronic properties of diarylethene compounds was studied. When nitrogen atom of pyridine ring in the same position, their absorption maximum closed-ring isomers, the photoconversion ratio and the cyclization reaction quantum yield of naphthalene systems are samller than that of benzothiophene systems; however, the fluorescence quantum yield and cycloreversion reaction quantum yield of naphtha lene systems are bigger than that of benzothiophene systems.