Stable frustrated phases in chiral liquid crystals derived from optically active (R)- and (S)-3-ethylmercapto-2-methylpropionic acids

Highly optically pure (R)- and (S)-3-ethylmercapto-2-methylpropionic acids were synthesized by using optically active (D)- and (L)-2,10-camphorsultams as chiral auxiliaries, respectively. Their derivatives, (R)- and (S)-EMMPNmB (m=6-12), were prepared for investigation. Microscopic texture observations demonstrated that the materials possess three stable frustrated phases: BP, TGB_A* and TGB_C* phases. Interestingly, it was found that the N* phase behaves as an intermediary phase between BP and TGB_A* phases in a rather narrow temperature range (calc. 0.5-1.4°C). A study of the racemic mixture, (±)-EMMPNmB (m=10), indicated that the chirality of the molecule could suppress the formation of smectic phases in the heating process. An increase of alkyl chain length favoured the formation of the TGB phases particularly, in accompaniment with a change of TGB phases from monotropic to enantiotropic. Moderate maximum P _S values (calc. 14-19 nC cm^-2) and apparent tilt angle (calc. 20°) were obtained for the TGB_C* phase in a surface stabilized ferroelectric liquid crystal geometry.     

Synthesis and evaluation of dinaphthylacetylene nematic liquid crystals for high-birefringence materials

We synthesised 1,2-bis(6-alkoxy-2-naphthyl)acetylene as a new dinaphthylacetylene liquid crystal (LC) compound with alkoxy tails of length m (DNA–OCm) and characterised their phase behaviour by polarising optical microscopy and differential scanning calorimetry, where all compounds exhibited a nematic phase. Also, we measured the actual, and not extrapolated, Δn values of this target compound, and our results show the birefringence potential of the pure LC compound. They have high birefringence values, with the highest value of approximately 0.5 obtained for DNA–OC2 at 550 nm at 10°C above the nematic?crystal transition temperature.     

Experimental investigation of liquid crystals in the millimetre frequency range

Dielectric properties of n·CB (n = 5, 6, 7, 8) liquid crystals (LCs) are investigated in the frequency intervals of 50–80, 120–160 GHz, and at 0.6 THz. The measurements are carried out in the millimetre wave range by the resonance method and with use of a reflectometer designed on the basis of a Michelson interferometer and quasi-optical metal-dielectric waveguides. Of most interest are the room temperature measurements of the birefringence of LCs. These measurements show that LCs can be used as polarisation transformers in the short wavelength region of the millimetre wave band and the long wavelength region of the sub-millimetre wave band.     

矩形晶格微结构光纤偏振拍长稳定性的优化

针对纤芯两侧具有一对大圆孔的矩形晶格微结构光纤,分别在两个正交方向上进行压缩或伸展,利用多种非对称结构的双折射相互平衡与补偿,抑制双折射随波长的非线性变化。应用全矢量有限差分波束传播法数值模拟分析了横向伸缩形变对模式双折射和偏振拍长色散特性的影响。通过优化设计,找出了合适的伸缩因子,有效降低了偏振拍长的波长敏感性。在1.0~2.0μm波长范围内,偏振拍长值在90.7~95.3 mm之间变化,相对变化率约为5%。这种矩形晶格微结构光纤适于制作宽带1/4波片。     

光诱导单电子转移反应合成氮杂环脯氨酸肽

以脯氨酸为起始原料合成了四个光反应底物N-(末端三甲基硅苄基脯氨酸肽链)邻苯二甲酰亚胺(4),并在甲醇溶剂中进行了光反应.结果表明,4的光致激发态分子内发生单电子转移反应,生成双离子自由基8,电子沿着化学键在给电子杂原子问转移,达到共振平衡,离去基团离去使平衡向末端杂原子方向移动,高选择性地生成分子内端位双自由基9,自...     

椭圆孔微纤芯光子晶体光纤的数值模拟

提出了一种在纤芯引入四个近矩形排列的椭圆空气孔,包层空气孔呈阶梯结构的高双折射光子晶体光纤,采用全矢量有限元方法,对光纤基模的模场分布、双折射、色散、限制损耗、有效模面积及非线性系数等特性进行了数值模拟.这种设计为获得高双折射光子晶体光纤提供了一种新的方法,为改善光子晶体光纤其他性能(如色散、非线性特性)提供了一种新的...     

Photoinduced Multiple Effects to Enhance Uranium Extraction from Natural Seawater by Black Phosphorus Nanosheets

Based on the photoinduced photothermal, photoelectric, and photocatalytic effects of black phosphorus (BP) nanosheets, a BP‐PAO fiber with enhanced uranium extraction capacity and high antibiofouling activity is fabricated by compositing BP nanosheets into polyacrylamidoxime (PAO). The photothermal effect increases the coordination interaction between UO₂²⁺ and the functional amidoxime group, and the photoelectric effect produces the surface positive electric field that exhibits electrostatic attraction to the negative [UO₂(CO₃)₃]^4?, which all increase the capacity for uranium adsorption. The photocatalytic effect endows the adsorbent with high antibiofouling activity by producing biotoxic reactive oxygen species. Owing to these three photoinduced effects, the photoinduced BP‐PAO fiber shows a high uranium adsorption capacity of 11.76 mg g^?1, which is 1.50 times of the PAO fiber, in bacteria‐containing natural seawater.     

Study of Interfacial Charge Transfer from an Electron Rich Organic Molecule to CdTe Quantum Dot by using Stern-Volmer and Stochastic Kinetic Models

Photoinduced electron transfer (PET) from N-methylaniline (NMA) to a photoexcited CdTe quantum dot (QD*) is studied in toluene. The PET mechanism at low to moderate quencher (NMA) concentrations (<0.08 M) remains mostly collisional with some contributions from QD-NMA complex formation. However, at high quencher concentrations (>0.10 M), QDs form larger numbers of static complexes with NMA molecules leading to a steep positive deviation in the steady-state Stern–Volmer curves. An isothermal titration calorimetry (ITC) study confirms the formation of QD-NMA complexes (K∼150 M⁻¹) at high quencher concentrations. Fitting our experimental data using a stochastic kinetic model indicates that the number of NMA molecules attached per QD at highest NMA concentration (∼0.16 M) used in this study decreases from ∼0.76 to ∼0.47 with reducing the QD size from ∼5.2 nm to ∼3.2 nm. However, the PET rate increases with decreasing QD size, which is commensurate with the observation that the chemical driving force (ΔG) increases with decreasing the QD particle size. We have analyzed the PET kinetics mainly by using Stern-Volmer fittings. However, in some cases Tachiya's stochastic kinetic model is used for stoichiometric analysis, which seems to be useful only at high quencher concentrations. The measured PET rate coefficients in all the cases are found to be at least an order of magnitude lower when compared to the diffusion-controlled rate of the reaction medium.