Synthesis And Properties Of New Unsymmetrical Photochromic Diarylethenes Bearing Naphthalene Moiety

Organic photochromic diarylethenes have become one of the most promising candidates of photoelectric materials because of their remarkable thermal stability, excellent fatigue resistance, and notable physical and chemical properties. Diarylethenes have many potential applications in erasable high-density information storage, optical switches, optical memories, and full-displays. Currently, design and synthesis of novel diarylethenes as well as study of their physicochemical properties are still hotspots.In this thesis, naphthalene and perfluorocyclopentene diarylethenes skeletons were synthesized. Their structures are characterized by NMR, IR and elemental analysis. Eighteen diarylethene crystals were prepared and some of their structures are determined by single-crystal X-ray diffraction analysis. The effects of such the heterocyclic aryl rings effects, double six-membered ring skeleton and the position of the substituents on the optoelectronic properties of these compounds were investigated in detail. The main outcomes are described briefly as follows.1. Photochromic properties of these diarylethenes in different medium such as in hexane solution, PMMA film and crystals were studied. The results showed that all of these diarylethenes exhibited good photochromic properties in solution and PMMA film except diarylethenes DT-23～25, which bear double six-memebered ring and have electron-withdrawing groups on benzene. However, the photochromism of these diarylethenes in crystal states are weak.2. The substituents and their positions, different six-membered aryl rings and the species of the heterocyclic aryl rings, have notable effects on the properties of these diarylethenes. Firstly, compared to the parent diarylethene DT-3, whose terminal benzene ring has no substituents, no matter replacing the hydrogen atom at the meta-position of the therminal benzene ring with electron-withdrawing or electon-donating substituent, the cyclization quantum yield of the hybrid diarylethenes bearing naphthalene and thiophene increased. Additionally, position effect of chlorine atom suggested that the absorption maxima (closed-ring isomer), the cyclization quantum yield, and the molar absorption coefficients of both the open-and closed-ring isomers were increased, whereas the cycloreversion quantum yield decreased along with the chlorine atom attached to the terminal benzene ring from the ortho-to meta-to para-position. Secondly, a new class of unsymmetrical photochromic diarylethenes based on of two six-memebered backbones with naphthalene moiety was prepared. The results demonstrated that cycloreversion quantum was gradually increased along with the aromatic stabilization energy of six-membered aromatic ring. Thirdly, a new series of diarylethenes bearing naphthyl moiety and heterocyclic aryl rings designed and synthesized. The results showed that the absorption maxima and the cycloreversion quantum are gradually enhanced along with increasing electron cloud density of heterocyclic aryl rings system, but the molar absorption coefficients and cyclization exhibited a reverse trend.3. The results of fatigue resistance study show that all the diarylethenes present good fatigue resistance both in solution and solid medium except asymmetric diarylethenes bearing double six-memebered ring backbone. The fatigue resistance of diarylethenes based on naphthalene ring was a little better in solution than in solid medium. Additionally, the thermal stabilitiy of some diarylethenes was also investigated. It was concluded that all of the diarylethenes have good thermal stabilitiy at room temperature and80℃. However, the asymmetric diarylethenes bearing double six-memebered ring backbone have relative poor thermal stability at80℃.4. The fluorescence spectra of diarylehtene compounds both in hexane solution and in PMMA amorphous film were determined. First, the diarylethene compounds exhibited relative strong fluorescence at the open-ring isomer whereas the closed-ring isomer very weak fluorescence or non-fluorescence. Second, the fluorescence emission intensitiy of the hybrid diarylethenes containing naphthyl and thienyl moieties had different degree increase, when electron-donating or electro-withdrawing group replaced the hydrogen on meta-postion of the terminal benzene. Third, due to the higher aromatic stabilization energy of the double six-membered aromatic ring than that of hybrid diarylethenes bearing naphthyl and thienyl structures, the former result in the cyclization quantum decreased and ultimate give rise to the fluorescence modulation efficiency prominent decline.5. Electron-donating/withdrawing ability of different substituents had a significant effect on the electrochemical behaviour of these diarylethenes. In this thesis chose several types of diarylethenes and investigated their electrochemical properties. The results showed that different electron-donating/withdrawing substituents and the position of substituents had a huge impact on the electrochemical behaviors of these compounds. Compared with open-ring isomer, ring-closed isomers generally had longer conjugation length, which lead to the oxidation potential onsets of the closed-ring isomers lower than that of the open-ring isomers.