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1.
1INTRODUCTIONThecrystalofureaisanonlinearopticalmaterial(13andcanbeprepareanopticalparameterocillator(OPO)element[2).LargeperfectcrystalshavebeengrownbysO.lutionmethod[3i,v!'athez-directionrestrictedgrowth..thed,thedirectionwiththehighestgrowthspeed.However,nodetailedinformationwasgivenondislocationsandstrainfeaturesrevealedbyX-raydiffractiontopography"'.Weconcentrateonstudyofthestructuraleffectsonthedefectiveformationandgrowthmorphology.foeureacrystalcrystallizesinthete-tragonalsystem"…  相似文献   

2.
三维SiO2欧泊模板溶剂热法制备硫化锌光子晶体   总被引:2,自引:0,他引:2  
以单分散二氧化硅微球在重力场下自组装得到的三维有序欧泊(opal)为模板,采用溶剂热法在模板空隙内生长ZnS晶体,从而制备高质量的硫化锌基光子晶体. 通过X射线衍射(XRD)和Raman光谱证明ZnS晶体为闪锌矿结构且晶体质量较好,并对其生长机理进行了讨论. 通过场发射扫描电子显微镜(FESEM)和紫外-可见分光光度计对所合成的ZnS/opal复合物与ZnS反欧泊结构进行了表征,结果表明两种结构都保持了欧泊三维有序性,并且在Г-L方向(垂直于(111)方向)上出现了布拉格衍射峰,说明其具有良好的光子晶体特性.  相似文献   

3.
Anthracene–pentiptycene hybrid systems 1-Cn , where n refers to the number of carbon atoms in the linear alkyl chain, crystallize in three different polymorphs, denoted Y (yellow), G (green), and B (blue) forms in terms of the fluorescence color. While all Y-form crystals show the same yellow-to-blue fluorescence color response to the photomechanical stress generated by the anthracene [4+4] photodimerization reaction, the four G forms exhibit distinct photomechanofluorochromism (PMFC): from green to blue for G-1-C4 , to orange for G-1-C7 , to red for G-1-C8 , and to red then blue for G-1-C9 , and the B forms show no photochromic activity. The intriguing RGB three-color PMFC and abnormal topochemical reactivity of G-1-C9 are attributed to inherent softness of the crystal lattice.  相似文献   

4.
Stilbazole and stilbazolium derivatives with dialkylaniline as electron pushing substituents and pyridine or pyridinium substituents as electron drawing substituents were synthesized and their aggregation behaviors were studied by UV‐visible, fluorescence and surface photovoltage spectroscopies. Experimental results indicate that the formation of aggregates can be mediated by the electron drawing ability of the substituents introduced for those compounds all bearing strong electron pushing substituent. When the electron drawing substituent is pyridine group, the molecules tend to aggregate in head‐to‐tail manner, whereas the substituent is pyridinium group, the molecules tend to aggregate in face‐to‐face manner. The effect of electron pushing and drawing ability of the substituents on the aggregation behavior is further analyzed in terms of frontier orbital interactions.  相似文献   

5.
离子液体与传统有机溶剂萃取性能的比较研究   总被引:12,自引:3,他引:12  
付新梅  戴树桂  张余 《分析化学》2006,34(5):598-602
利用离子液体1-甲基-3-丁基咪唑六氟磷酸盐(C4)和1-甲基-3-己基咪唑六氟磷酸盐(C6)以及传统有机溶剂二氯甲烷作萃取溶剂,研究了它们在不同条件下萃取水环境中的环境内分泌干扰物壬基酚和辛基酚的萃取性能,结果表明,二氯甲烷达萃取平衡的时间(20min)比离子液体(60min)短;当水相的pH值发生变化时,离子液体和二氯甲烷的萃取率均随pH值的增大而降低;盐析效应显示离子液体受盐效应影响很小,而二氯甲烷受盐效应的影响大;壬基酚和辛基酚浓度增大导致萃取率降低;离子液体和二氯甲烷的萃取率均随温度的升高而升高,适当的提高温度有利于萃取率的提高。用离子液体萃取水溶液中有机物质,表现出和传统萃取溶剂相类似的一些性质,如酸度、温度、分析物的浓度均对其萃取率有一定影响。  相似文献   

6.
Under the irradiation of the ultraviolet light, Isoeugenol (I) undergoes dimerization in acetone to give diisoeugenol (II) and dehydrodiisoeugenol (III). The structures are determined by the comparison of the mixed m. p., I. R. spectra and T. L. C. with synthesized authentic samples. Also the photoreaction mechanism is discussed in detail. The reaction represents a new type and as an exception of photochemical process for the C=C double bond in conjugation with aromatic ring that generally dimerizes to produce cyclobutane type derivatives.  相似文献   

7.
袁耀锋  王文峰 《化学教育》2015,36(10):74-77
采用B3LYP/DFT方法和6-311+G**基组优化了苯酚、苯甲醚、苯胺、苯氧基负离子以及对甲氧基苯甲醛和对羟基苯甲醛等6个化合物的分子结构。通过比较这些化合物的键长和π电子布居数,推断出4个活化基团对苯环的活化能力有如下顺序;-OH3 2 -。也计算了苯酚、苯甲醚、苯胺和苯氧基负离子发生F-C甲基化反应的速率决定步骤的自由能,结果显示这4个化合物的反应活性顺序如下;苯酚< 苯甲醚< 苯胺< 苯氧基负离子。结论是;羟基活化苯环的能力略弱于甲氧基,但是氧负离子活化苯环的能力比羟基和甲氧基高得多。  相似文献   

8.
In this study, we investigated structural changes in alpha-glucosidase during urea denaturation. Alpha-glucosidase was inactivated by urea in a dose-dependent manner. The inactivation was a first-order reaction with a monophase process. Urea inhibited alpha-glucosidase in a mixed-type reaction. We found that an increase in the hydrophobic surface of this enzyme induced by urea resulted in aggregation caused by unstable folding intermediates. We also simulated the docking between alpha-glucosidase and urea. The docking simulation suggested that several residues, namely THR9, TRP14, LYS15, THR287, ALA289, ASP338, SER339, and TRP340, interact with urea. Our study provides insights into the alpha-glucosidase unfolding pathway and 3D structure of alpha-glucosidase.  相似文献   

9.
4,6,4'-Trimethylangelicin and 6,5'-dimethylangelicin form C4-cyclodimers when irradiated in water-ethanol solution. The former compound yields a pyrone-pyrone dimer similar to that formed by psoralens. 6,5'-Dimethylangelicin forms both pyrone-pyrone and pyrone-furan dimers; this unusual dimer has the cis-syn configuration.  相似文献   

10.
After base treatment of ZSM‐5 crystals below 100 nm in size, TEM shows hollow single crystals with a 10 nm shell. SEM images confirm that the shell is well‐ preserved even after prolonged treatment. Determination of the Si/Al ratios with AAS and XPS in combination with argon sputtering reveals aluminum zoning of the parent zeolite, and the total pore volume increases in the first two hours of base treatment. In corresponding TEM images, the amount of hollow crystals are observed to increase during the first two hours of base treatment, and intact crystals are visible even after 10 h of leaching; these observations indicate different dissolution rates between individual crystals. TEM of large, commercially available ZSM‐5 crystals shows inhomogeneous distribution of mesopores among different crystals, which points to the existence of structural differences between individual crystals. Only tetrahedrally coordinated aluminum is detected with 27Al MAS NMR after the base leaching of nano‐sized ZSM‐5.  相似文献   

11.
通过反-1,2-双(2-苯并唑基)乙烯(BBE)和反-1-(2-苯并咪唑基)-2-(2-苯并唑基)乙烯(BME)的光二聚反应合成了r-1,c-2,t-3,t-4-四(2-苯并唑基)环丁烷(BBC)和r-1,c-2,t-3,t-4-1,3-双(2-苯并咪唑基)-2,4-双(2-苯并唑基)环丁烷(BMC).用元素分析、红外、紫外、核磁共振谱、质谱及X射线衍射表征了二聚体的结构.BBC晶体属三斜晶系,空间群为P1.晶胞参数:a=0.64684(13)nm,b=1.3242(3)nm,c=1.6245(3)nm;α=74.66(3)°,β=78.77(3)°,γ=76.06(3)°,Z=2.BBC晶胞中分子有两种取向,两种取向不同分子的苯并唑平面间存在着π-堆积现象.π-堆积面间的距离在0.330~0.376nm之间,与石墨晶体中分子平面片层间的距离非常接近.BBC和BMC都具有中心对称性,光二聚反应的高度立体选择性以及BBE和BME的光二聚反应不受空气中氧的影响的事实表明它们是经激发单线态历程以面对面的方式进行二聚反应的,本文检测到了BBE和BME在高浓度溶液中的激基缔合物荧光.  相似文献   

12.
13.
[18]‐ and [24]Annulenes condensed with three pyrene or phenanthrene ring systems show, in solution, especially in apolar solvents, a strong aggregation evidenced, for example, by concentration‐dependent 1H‐NMR spectra. However, the fluorescence bands and the fluorescence lifetimes of these compounds depend only to a minor extent on the concentration and correspond essentially to the measurements obtained for the monomer. Among several models discussed, one is favored in which aggregates can be excited, but the emission is due to an almost undisturbed monomer. Even for the pyrene system, an excimer fluorescence cannot be detected. Nevertheless, short‐lived excimers are responsible for the regio‐ and stereoselective photodimerization to belt cyclophanes.  相似文献   

14.
15.
Conducting reactions in environmentally benign conditions is one of the major objectives of “green chemistry.” In this context, developing ways to conduct reactions in water seems obvious. In this report, we present our results on photodimerization of select guest molecules placed within the rigid reaction cavity of a water-soluble cavitand, octa acid. The results presented herein highlight the value of a supramolecular approach in achieving selectivity in photoreactions and opening reaction pathways that are latent in solution chemistry.  相似文献   

16.
将快速Monte Carlo方法与分子动力学方法相结合, 研究了不同种类有机分子在Al3P4O3-16计量比的二维层状磷酸铝形成中的模板能力. 依据主-客体之间非键相互作用能(包括范德华能、氢键能和库仑能), 可合理地解释已知实验现象, 并能有效地预测出适于形成某一特定无机层结构的有机胺模板剂. 通过选择理论预测的有机胺分子作为模板剂, 成功地合成了二维层状磷酸铝化合物Al3P4O16*1.5H3NC6H10NH3.  相似文献   

17.
Irradiation (λ > 300 nm) of dimethyl 3 - dehydrogibberellenate 1, as a heteroannular dienone, in t-BuOH (10?2 M) for 2 hr led to cyclobutane-type photodimer A in 85% yield. However, irradiation of 1 under the same conditions but for 3 hr gave not only photodimer A but also two other photodimers B and C which were found to be the products of photoepimerization reaction of A. The stereochemistry of A, B and C was fully elucidated on the basis of physico-chemical techniques. At lower concentration (10?4 M) of A in t-BuOH, irradiation with λ 254nm and λ 313 nm resulted in β-cleavage to 1.  相似文献   

18.
Irradiation (λ>400 nm) of solid pleiadiene ( 1 ) yields a single, head-to-head [π4s+π4s]-photodimer ( 2 ) the structure of which was determined by X-ray analysis. The formation of 2 is entirely suppressed at 77 K, since properly oriented pairs of molecules arise only from thermal disorder in crystals of 1 . Upon pyrolysis (80°), the strained photodimer 2 rearranges to the [π2s + π4s] dimer 3 by a ‘forbidden’ suprafacial [1,3]-C-atom migration. Both 2 and 3 are reconverted to 1 by UV. irradiation in solution, but the latter, ‘forbidden’ photoreaction is suppressed at 77 K . Discrepancies of the experimental observations with the predictive schemes of Kaupp or Michl are discussed.  相似文献   

19.
1,4-Dicinnamoylbenzene crystals photodimerize readily via a double [2+2] cycloaddition into the corresponding tricyclic dimer, which consists of two cyclobutane rings and a macro ring bridged by two phenylene linkages.  相似文献   

20.
The intramolecular photodimerization of thymine bases present on the side chain of a variety of synthetic oligomers and polymers was studied in detail in various organic solvents, and particularly in the case of thymine-containing polylysines, over a wide range of pH. Effects of solvents, presence of the complementary base, and spacers on the photoreaction were examined, and the conformational changes of the polymers were discussed in relation to their functionalities. Intermolecular photodimerization was further studied, and its applicability to photoresists was shown.  相似文献   

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