Modulation of photoswitching profiles by 10,11-dialkoxymethyl substituents in c(2)-symmetric dibenzosuberane-based helicenes

A series of C₂‐symmetric, 10,11‐disubstituted dibenzosuberane (DBS)‐based helicenes 6 a – c with a common 7‐bromo‐α‐tetralin‐based bottom fragment were synthesized. Their absolute stereochemistry was determined to be 10R,11R,P after reductive desulfurization of the corresponding (10R,11R,1′S)‐episulfides with complete stereospecificity. Photoisomerization of the diastereomerically pure (P)‐ 6 c in hexane led to virtually exclusive formation of the opposite M‐form diastereomer (P/M′, <1:>99) at 290 nm. The preferential return of (M′)‐ 6 c to (P)‐ 6 c was also achieved with high selectivity (P/M′, 90:10) at 330 nm. Molecular simulations of (P)‐ 6 c and (M′)‐ 6 c with both DBS conformations suggest that the selectivities of photoswitching are controlled by the conformation of the top DBS template as evidenced by their ¹H NMR spectra. Doping 6 c into a nematic liquid crystal (E7) led to a cholesteric mesophase with modulated pitches, reversible helical senses, and with a switch memory of ternary logic.     

Chiral Auxiliaries as Emerging Tools for the Asymmetric Synthesis of Octahedral Metal Complexes

New methods for the stereocontrolled synthesis of octahedral metal complexes are needed in order to fully exploit the stereochemical richness of the octahedron in the fields of catalysis, materials sciences, and life sciences. Whereas a large body of work exists regarding the diastereoselective coordination chemistry with chiral ligands, such efforts are restricted to certain carefully designed chiral ligands which remain in the coordination sphere. The emerging strategy of chiral‐auxiliary‐mediated asymmetric synthesis holds promise to solve the problem of controlling relative and absolute configuration in octahedral metal complexes in a general fashion, thus hopefully in the future providing access to any desired optical active octahedral metal complex without the need for chiral separations. This short review will summarize reported examples of chiral auxiliaries applied to the asymmetric synthesis of octahedral metal complexes.     

Growth and Spectral Characteristics of Yb3＋-doped LiGd（MoO4）2 Crystal

The Yb3+-doped LiGd(MoO4)2 crystal with the size up to Φ20×30 mm3 has been grown by Czochralski technique.The polarized room temperature absorption and emission spectra have been investigated.This crystal exhibits a broad absorption band centered at 975 nm with an FWHM of 43 and 59 nm for π-and σ-polarization,respectively,and the corresponding maximal absorption cross-sections are 3.36 and 2.42×10-20 cm2.The emission broadband has an FWHM of 47 and 54 nm for π-and σ-polarization,respectively,with the corresponding emission cross sections of 3.92 and 3.34 × 10-20 cm2 at 1020 nm.The measured fluorescence lifetime is 287 μs.     

Controlled Synthesis of Sea-urchin-like ZnO Nanomaterials with the Aid of Ethylene Glycol Using a Solvothermal Method

Sea-urchin-like ZnO nanomaterials were successfully synthesized by decomposition of zinc acetate precursor in the presence of sodium hydroxide and ethylene glycol(EG) in an ethanol solution using a solvothermal method at 180 ℃ for 12 h.The crystalline phase and morphology of the resultant nanomaterials were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),selected-area electronic diffraction(SAED) and high-resolution electron microscopy(HRTEM).Interestingly,the sizes and prod length of the samples can be easily tuned by changing the amount of directing agent EG and keeping other reaction conditions unchangeable.On the basis of our experimental outcomes,EG-controlled-nucleation-growth formation mechanism was proposed to correspond for the sea-urchin-like ZnO growth processes.And the photoluminescence(PL) spectra of the as-selected samples were measured at room temperature,presenting two emission peaks centered at～388 and 480 nm.     

飞秒光学外差光学克尔效应和低频拉曼光谱技术研究离子液体[bmim][PF6]的低频光谱

利用飞秒光学外差光学克尔效应技术获得了咪唑类离子液体1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF6])体系中反映分子间相互作用的低频光谱. 结果分析中, 利用Brownian振子时间相关函数的精确表达式对光学克尔效应动力学数据中的核振动部分进行模拟, 在时域上获得各个振动组分的时间演化行为, 并进而通过快速Fourier变换获得各个振动组分的频域光谱和总加和光谱. 此外还利用低频拉曼光谱技术测量了离子液体[bmim][PF6]的低频光谱, 并和飞秒光学外差光学克尔效应实验的结果进行对比, 发现两种方法获得的低频光谱相近. 实验结果表明Brownian振子时间相关函数的精确表达式可用来解析离子液体体系中低频振动的时间演化行为.     

Growth and characterization of L‐alanine doped KDP crystals

Potassium Dihydrogen Phosphate (KDP) is an excellent inorganic nonlinear optical (NLO) material with different device applications. Most of amino acids possess NLO property; therefore, it is of interest to dope them in KDP crystals. In the present study, amino acid L‐alanine doped KDP crystals were grown by slow aqueous solvent evaporation technique. The doping of L‐alanine was confirmed by the paper chromatography, the CHN analysis and the FT‐IR spectroscopy. The powder XRD was carried out to assess the single phase nature of the samples. The effect of doping on thermal stability of the crystals was studied by TGA and the kinetic and thermodynamic parameters of dehydration were evaluated. As the amount of doping increased the thermal stability of crystals decreased. However, the second harmonic generation (SHG) efficiency and the UV‐Vis spectroscopy studies indicated that as the L‐alanine doping increased the SHG efficiency and optical transmission percentage increased. The dielectric behavior of the samples has been studied. The variation of dielectric constant, dielectric loss (tanδ), a.c.resistivity and a.c.conductivity with frequency of applied field in the range from 100 Hz to 100 kHz was studied. The dielectric constant and dielectric loss decreased with increase the value of frequency of applied field. The dielectric constant and the dielectric loss values of L‐alanine doped KDP crystals were lower than the pure KDP crystals. The results are discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

有机液芯光纤拉曼谱测量的研究

我们选用CCl4和CS2混合溶液作为芯液制作了有机液芯光纤,采用后向泵浦的方式测量了光纤的拉曼光谱.实验中发现,随着溶质浓度和光纤长度的变化,拉曼谱强度也随之变化,并存在溶质最佳浓度和最佳光纤长度,这与理论分析值相符,并发现随着溶质浓度的降低,拉曼光谱线宽变窄.     

大相对孔径长波红外光学系统无热化设计

 针对目前许多军工仪器红外成像系统的结构简单、体积小、质量轻的无热化设计要求,采用光学被动式方法对8 μm~12 μm波段、相对孔径为1的红外光学系统进行了无热化设计。具体光学系统参数：F=1,f=60 mm,2ω=11.4°。设计结果：在-40℃~60℃工作范围内,该系统的调制传递函数（MTF）接近衍射极限,空间分辨率在20 lp/mm处,中心视场传函接近0.7,边缘视场传函大于0.6。其设计结果满足系统的无热化设计要求。     

稳态力输出的实验与理论研究(英文)

对低频共振情况下激光引擎的基本特性与其理论预测值做了比较,并研究了实现这些技术的重要步骤,认为基于不同学科与工业组织之间的合作,不久的将来会实现利用累计势能来驱动微型汽车。     

基于FPGA的视频信号数字化光纤传输实验接收装置的设计与实现

介绍了以FPGA为主控芯片,以光纤为通讯媒介的视频信号数字通信实验装置的设计实现过程,并对电路各个模块的功能及实现加以说明.电路在Altium Designer中设计完成,采用分模块式的设计,结构清晰,易于实现.在QuartusⅡ环境下用VerilogHDL语言进行编程并对程序进行仿真.该装置已做成了实体,可以实现视频信号的传输.