Synthesis And Properties Of New Unsymmetrical Diarylethenes Bearing A Thiazole/Isoxazole Moiety

Diarylethenes are the most promising candidates for optoelectronic devices because of their remarkable chemical and thermal stability of isomers, excellent fatigue resistance and excellent physical and chemical properties. Diarylethenes have received considerable attention because of their potential applications in erasable high-density information storage, optical memories, optical switches, and full-displays. Currently, design and synthesis of novel diarylethenes as well as investigations of their properties are both fundamental research and hotspots.In this dissertation, we have synthesized twenty-six new asymmetric diarylethenes with thiazole or isoxazole ring, and their structures are identified by NMR, IR and elemental analysis. Twelve diarylethene crystals are prepared, and their structures are determined by single-crystal X-ray diffraction analysis. We investigated the effects of the heterocyclic aryl rings species, the electron-withdrawing/donating ability, and the position of the substituents on the optoelectronic properties of these compounds. Preliminary optical storage tests were performed using diarylethenes as recording media. The main outcome described briefly as follows:Photochromic properties of these diarylethenes in diffrent medium were studied. On one hand, these diarylethenes we have synthesized showed good photochromic properties in solution and PMMA diaphragm except diarylethenes bearing both isoxazole and benzene ring. Crystals DT-2~5 and DT-11~15 showed good photochromic properties,but DT-21, DT-23, DT-26 have no photochromic properties.The species of the heterocyclic aryl rings and the substituents have notable effects on the properties of these diarylethenes such as absorption maxima, molar absorption coefficients, cyclization/cycloreversion quantum yields, and photoconversion ratios at photostationary state. Firstly, the cyclization quantum yields of diarylethenes bearing thiazole were much higher than those bearing isoxazole ring, but the cycloreversion quantum yields have opposite trend. Secondly, electron-donating substituents could enhance the cyclization quantum yields whereas electron-drawing substituents could enhance the cycloreversion quantum yields of the diaylethenes bearing both thiazole and benzene ring. Finally, compared with the unsubstituted parent compound, the cyclization quantum yields increased obviously whereas the cycloreversion quantum yields decreased notably when different substituent group was attached at p-position on the terminal benzene ring of diarylethenes bearing isoxazole. Strong electron-withdrawing/donating substituent group could improve the photoconversion ratios of those diarylethenes at photostationary state. Strong electron-drawring substituent could improve the absorption maxima and molar absorption coefficients of the open-ring isomer whereas the electron-donating substituent could improve the absorption maxima and molar absorption coefficients of the closed-ring isomer.The fatigue resistance of some diarylethenes was also investigated. On one hand, the fatigue resistance of diarylethenes in PMMA film was much better than those in hexane. On the other hand, the fatigue resistance of diarylethenes bearing an isoxazole ring was much stronger than that bearing a thiazole moiety, especially in PMMA amorphous film. After 200 repeated cycles, compounds DT-11~15 still showed good photochromism with the absorbance maintained above 93% basically.The fluorescence spectra of diarylehtenes both in hexane and in PMMA amorphous film have been investigated. Firstly, the compounds exhibited strong fluorescence at the open-ring isomer whereas the closed-ring isomer without or very weak fluorescence. Secondly, the concentration effect on the fluorescent property was also remarkable. In certain concentration range, fluorescence intensity increased with the increase of the solution concentration, but to a certain degree, fluorescence intensity weakened gradually until quenches. Once more, the electron-withdrawing/donating ability and the position of the substituents have notable effects on fluorescent emission peaks and fluorescent emission intensities of the diarylethenes bearing thiazole ring. The emission peaks of diarylethenes DT-1~3 were observed at 411, 444 and 448 nm, respectively. Remarkable bathochromic shift of the ?uorescent emission were observed and their emission intensity increased evidently when the substituents position from the ortho- to meta- to the para-positions. Strong electron-withdrawing substituent could reduce the emission intensity of the diarylethenes bearing both thiazole and benzene ring. Finally, the emission peaks of diarylethenes DT-11~15 bearing an isoxazole ring gradually shifted to a shorter wavelength in hexane (from 436 to 396 nm) when going from electron-donating to electron-withdrawing groups.The electrochemical tests indicated that different electron-donating/withdrawing substituents had a remarkable effect on the electrochemical behaviors of these diarylethenes. Under the same experimental condition, the oxidation potential onsets of the open-ring isomers were clearly higher than those of the closed-ring isomers because of molecular conjugate system of the closed-ring was extended.Furthermore, we carried out four types of polarization holographic optical storage, three kinds of multiplexing storage and optical storage tests on PMMA film using diarylethenes as the recording media. The results demonstrated that optical storage was carried out successfully using diarylethenes as medium...