Photochemistry of azobenzene in sol-gel systems

The photophysical and photochemical behavior of azobenzene incorporated into sol-gel systems was studied. Sols doped with azobenzene were prepared by the hydrolysis of tetramethoxysilane. The absorption spectra of azobenzene in sols with and without HCl as a catalyst showed photochromism; UV irradiation changes trans-azobenzene to cis-azobenzene, which returns to trans-azobenzene by successive visible light irradiation. The results indicate that azobenzene is not protonated in the sol prepared by the present conditions. The absorption spectra showed that the azobenzene-doped xerogel prepared without HCl is mostly adsorbed on silica surfaces by the hydrogen bonding between the azo groups and silanol and/or water molecules. The adsorption did not affect photochromic behavior and photo-reversible changes were observed in the xerogels. UV photolysis of the azobenzene-doped xerogel prepared with HCl so produced protonated benzo[c]cinnoline that photochromic behavior was deteriorated. Surface modified xerogels were prepared from the mixture of tetraethoxysilane and methyltriethoxysilane in order to make clear the effect of the surface silanol groups. It was shown that the formation of the protonated benzo[c]cinnoline is suppressed by the introduction of Si-CH₃. These present results confirm that the acidic sites of Si-OH₂⁺ of xerogels play an important role in the photochemical reaction of azobenezene in silica xerogels.     

吡咯俘精酸酐的光致各向异性研究

将有机光致变色化合物—吡咯取代俘精酸酐掺杂于PMMA中形成薄膜.在紫外光照射下,薄膜由无色态转换为呈色态.用650 nm线偏振激光照射薄膜,在由呈色态转变为无色态时产生光致各向异性.对633 nm的探测光具有正单轴晶体特性,光轴方向平行于激发光振动方向,光致二向色性率(D_⊥-D_∥)可达0.2,光致双折射率(n_∥-n_⊥)可达2×10^-3.实验还测量了光致各向异性与曝光量的特性曲线,发现最佳曝光量为13～20 J/cm²;理论分析了其原因.这些结果为俘精酸酐材料在光信息处理方面的应用提供了实验数据.     

Solvent effect on photochromism of a dithienylperfluorocyclopentene having diethylamino group

Some photochromic diarylethenes having polar substituents were synthesized, and their photochromic behavior was examined. They exhibited photochromism with the similar photoreactivity in a non-polar solvent. However, the photocyclization quantum yield of dithienylperfluorocyclopentene having diethylamino group was found to decrease in polar solvents. The yield in acetonitrile was estimated to be 60 times smaller than that in hexane. The yields determined in various solvents were found to be correlated with the solvent polarity parameter E_T(30). Such an effect was not observed in dithienylfluorocyclopentenes bearing methoxy or acetoxy group and in non-fluorinated dithienylcyclopentene bearing diethylamino group.     

配位键驱动的多卟啉阵列结构在纳米SiO2表面的组装及光电性能

制备了吡啶功能化的纳米二氧化硅(nanoSiO₂BPy), 并利用配位键驱动的层层自组装技术, 以四吡啶基锌卟啉(ZnTPyP)为链接单元, 在nanoSiO₂BPy表面构筑了含有(Pd/ZnTPyP)_n多卟啉阵列结构的有机-无机杂化材料. 利用热重、 紫外-可见吸收光谱和X射线光电子能谱跟踪分析了nanoSiO₂BPy@(Pd/ZnTPyP)_n杂化材料的组装过程. 结果表明, nanoSiO₂BPy@(Pd/ZnTPyP)₃杂化材料在150~450 ℃升温区间内质量损失17%, 可归结为组装在纳米SiO₂表面的多卟啉阵列和少量有机物的热分解. 紫外-可见和荧光光谱表明, 在nanoSiO₂BPy@(Pd/ZnTPyP)_n杂化材料中, 锌卟啉Soret带的吸收峰出现在426 nm处, 其Q带的荧光发射峰出现在605和655 nm处, 荧光寿命约为1.78 ns, 光谱数据均与锌卟啉在稀的二甲亚砜溶液中的结果接近, 表明组装在nanoSiO₂BPy表面的锌卟啉环之间相互作用较弱, 没有形成聚集体. 场发射透射电镜照片显示, 由于Pd/ZnTPyP的组装, nanoSiO₂BPy@(Pd/ZnTPyP)₃杂化材料的平均直径由原料的10~16 nm增加到15~20 nm. 杂化材料修饰电极的循环伏安曲线在-0.6~-2.4 V(vs. Ag/AgCl)范围内出现了2对不可逆的氧化还原峰, 归属于卟啉被氧化的电子转移过程. 探讨了nanoSiO₂BPy@(Pd/ZnTPyP)_n杂化材料作为光敏剂在光电转换、 光催化乙基紫精的还原和显色方面的应用.     

Bifunctional probe for Cu2+/Al3+ based on a diarylethene with a 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole unit

A new asymmetric perfluordiarylethene (1O) was synthesized using 4, 5-[bis-(5-ethylacetate-yl)-2-thienyl]-1H-imidazole as a functional group. 1O exhibited favorable reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light. Both of its open- and closed-ring isomers were found to be highly selective towards Cu²⁺ with significant absorption and color changes, which could be used as a ‘naked-eye’ colorimetric sensor for Cu²⁺ detection. Upon exposure to acid, its fluorescence dramatically enhanced by 14-fold with a color change from dark to bright cyan due to the formation of the protonated compound. Moreover, 1O showed obvious fluorescence “turn-on” signal response towards Al³⁺, and the detection limit for Al³⁺ was determined to be 4.8 × 10^?9 mol L^?1. Based on the fluorescence signals of 1O, a combinational stimuli logic circuit were designed by using the fluorescence intensity as the output signal with the inputs of lights, Al³⁺ and EDTA. Finally, 1O could be used as a biological probe for detecting intracellular Al³⁺ in a physiological environmental.     

A bifunctional probe for Al3+ and Zn2+ based on diarylethene with an ethylimidazo[2,1-b]thiazole-6-hydrazide unit

A new diarylethene with ethylimidazo[2,1-b]thiazole-6-hydrazide unit was synthesized, and its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of lights and metal ions in methanol. This new diarylethene exhibited high selectivity and sensitivity toward Al³⁺ and Zn²⁺. The addition of Al³⁺ and Zn²⁺ displayed excellent colorimetric response behaviour with the concomitant color change from colorless to yellow, which could be easily observed by the naked eye. Upon addition of Al³⁺, the fluorescence intensity was enhanced by 180–fold and the emission peak of 1O–Al³⁺ blue-shifted by 15?nm accompanied with a color change from colorless to bright blue. In contrast, when stimulated with Zn²⁺, its fluorescence intensity was enhanced by 35–fold and the emission peak of 1O–Zn²⁺ red-shifted by 16?nm with an evident color change from black to bright green. The LOD for Al³⁺ and Zn²⁺ were determined to be 2.97?×?10^?9?mol?L^?1 and 5.98?×?10^?9?mol?L^?1, respectively. Moreover, a logic circuit was constructed with the fluorescence intensity as the output signal responding to the light and chemical species as the inputs.     

含席夫碱基的螺吡喃双功能光致变色材料的合成及性质

设计合成了一系列含席夫碱基的螺吡喃双功能光致变色材料4a~4n. 通过1H NMR, IR和HRMS对其结构进行了表征. 研究了化合物在几种溶剂和PMMA膜中的光致变色性质, 研究了化合物4a在甲醇中, 以及化合物4a和4f在高分子介质聚甲基丙烯酸甲酯(PMMA)中的消色过程. 结果表明, 化合物4e在PMMA膜中光照后呈现出与其它化合物不同的颜色, 为罕见的绿色. 化合物4a在二氯甲烷溶液中有良好的荧光性能. 所合成的新型含席夫碱基的螺吡喃双功能光致变色材料在甲醇、二氯甲烷和环己烷溶液中及在PMMA膜中均表现出良好的光致变色性质.     

与二茂铁酰基相连的螺噁嗪的合成、结构及性质

在二环已基碳二亚胺(DCC)存在下, 将9′-羟基螺噁嗪与二茂铁甲酸进行酯化缩合, 合成了一种与二茂铁酰基相连的螺噁嗪衍生物2, 用核磁共振氢谱、碳谱、红外光谱、高分辨质谱和X射线单晶衍射对其结构进行了表征. 化合物2在几种有机溶剂中都表现出了良好的光致变色性质; 通过实验证明了在无冰水浴冷却条件下, 用高压汞灯照射时化合物2在二氯甲烷中表现出的特殊变色性是酸致变色的结果; 同时还研究了化合物2在固体PMMA薄膜中的光致变色性质. 在高压汞灯照射下,化合物2在二氯甲烷溶液中显示了良好的荧光性. 循环伏安法测定结果表明化合物2具有良好的氧化还原可逆性.     

Thermochromism of 1, 4-Bis[2-(4-pyridyl)ethenyl]-benzene Derivatives

Three kinds of thermochromic materials (DC8, DC12, DC16) were synthesized by linking the rigid 1, 4-bis[2-(4-pyridyl)ethenyl]-benzene (bpeb) with different lengths of alkyl chains. They exhibit remarkable fluorescent color changes under the irradiation of 365 nm light with elevating temperature, which is supposed to be caused by the transition between the crystal state and the amorphous state. Interestingly, the DC16 solid also has a photochromic character. It should be noticed that the phase transition temperatures of three materials measured by differential scanning calorimetry are higher than those of the fluorescence color changes during the heating process. Thus, the allochroic effect is attributed to the synergistic effect of both heating and photo-inducement (365 nm). Ethanol can turn the heated powder into the initial crystal again which indicates that their thermochromic behavior is reversible and makes the fluorescence recover.     

Synthesis and photochromism of novel unsymmetrical diarylethenes with an azaindole unit

A new class of unsymmetrical photochromic diarylethenes with an azaindole moiety has been firstly synthesized. Their properties, including photochromism, crystal structure, as well as fluorescence, were investigated systematically. The azaindole was connected directly to the central cyclopentene ring as a heteroaryl moiety and available to participate in the photoisomerization reaction. Each of the diarylethenes exhibited favorable photochromism, good thermal stability, remarkable fatigue resistance, and notable fluorescence switches in both solution and solid media. The substituents at the para-position of the terminal benzene ring affected evidently their properties: the electron-donating methoxy could be effective to enhance the cyclization quantum yield, while the electron-withdrawing cyano could shift the absorption maximum to a longer wavelength in both hexane and solid film. The results revealed that the introduction of azaindole moieties and different substituents played an important role in the photoisomerization process of these diarylethenes.