2D Organic Photonics: An Asymmetric Optical Waveguide in Self‐Assembled Halogen‐Bonded Cocrystals

Anisotropic organic molecular construction and packing are crucial for the optoelectronic properties of organic crystals. Two‐dimensional (2D) organic crystals with regular morphology and good photon confinement are potentially suitable for a chip‐scale planar photonics system. Herein, through the bottom‐up process, 2D halogen‐bonded DPEpe‐F₄DIB cocrystals were fabricated that exhibit an asymmetric optical waveguide with the optical‐loss coefficients of R_Backward=0.0346 dB μm^?1 and R_Forward=0.0894 dB μm^?1 along the [010] crystal direction, which can be attributed to the unidirectional total internal reflection caused by the anisotropic molecular packing mode. Based on this crystal direction‐oriented asymmetric photon transport, these as‐prepared 2D cocrystals have been demonstrated as a microscale optical logic gate with multiple input/out channels, which will offer potential applications as the 2D optical component for the integrated organic photonics.     

Trace and Density Results on Regular Trees

Potential Analysis - The boundary of a regular tree can be viewed as a Cantor-type set. We equip our tree with a weighted distance and a weighted measure via the Euclidean arc-length and consider...     

Nonenzymatic sensing of hydrogen peroxide using a glassy carbon electrode modified with graphene oxide,a polyamidoamine dendrimer,and with polyaniline deposited by the Fenton reaction

A highly sensitive electrochemical sensor is described for the determination of H₂O₂. It is based on based on the use of polyaniline that was generated in-situ and within 1 min on a glassy carbon electrode (GCE) with the aid of the Fe(II)/H₂O₂ system. Initially, a 2-dimensional composite was prepared from graphene oxide and polyamidoamine dendrimer through covalent interaction. It was employed as a carrier for Fe(II) ions. Then, the nanocomposite was drop-coated onto the surface of the GCE. When exposed to H₂O₂, the Fe(II) on the GCE is converted to Fe(III), and free hydroxy radicals are formed. The Fe(III) ions and the hydroxy radicals catalyze the oxidation of aniline to produce electroactive polyaniline on the GCE. The resulting sensor, best operated at a working potential as low as 50 mV (vs. SCE) which excludes interference by dissolved oxygen, has a linear response in the 500 nM to 2 mM H₂O₂ concentration range, and the detection limit is 180 nM. The sensor was successfully applied to the determination of H₂O₂ in spiked milk and fetal bovine serum samples.

Open image in new window

Graphical abstract Schematic presentation of a sensitive electrochemical sensor employed for detection of H₂O₂ in sophisticated matrices by using graphene oxide-PAMAM dendrimer as initiator container and Fe²⁺/H₂O₂ system as signal enhancer.

     

Organocatalytic asymmetric epoxidation reactions in water-alcohol solutions

The diastereo- and enantioselective organocatalytic epoxidation of alpha,beta-unsaturated aldehydes in aqueous solutions is presented. By the screening of the reaction conditions for the epoxidation of cinnamic aldehyde applying hydrogen peroxide as the oxidant and 2-[bis-(3,5-bis-trifluoromethyl-phenyl)-trimethylsilanyloxy-methyl]-pyrrolidine as the catalyst, a highly stereoselective reaction has been developed. The scope of the diastereo- and enantioselective organocatalytic epoxidation in aqueous solutions is documented by the asymmetric epoxidation of alpha,beta-unsaturated aldehydes with enantioselectivities up to 96% ee.     

Large-scale fabrication of tower-like, flower-like, and tube-like ZnO arrays by a simple chemical solution route

Large-scale arrayed ZnO crystals with a series of novel morphologies, including tower-like, flower-like, and tube-like samples, have been successfully fabricated by a simple aqueous solution route. The morphology and orientation of the obtained ZnO crystal arrays can be conveniently tailored by changing the reactants and experimental conditions. For example, the tower-like ZnO crystal arrays were obtained in a reaction solution system including zinc salt, ammonia, ammonium salt, and thiourea, and the orientation of these tower-like crystals could be controlled by the contents of these reactants. Flower-like ZnO arrays were obtained at lower temperatures, and tube-like ZnO arrays were obtained by ultrasonic pretreatment of the reaction system. The growth mechanism of the tower-like and tube-like ZnO crystals was investigated by FESEM. The results show that tower-like crystals grow layer by layer, while tube-like crystals grow from active nanowires. Ultrasonic pretreatment is proved to be effective in promoting the formation of active nuclei, which have important effects on the formation of the tube-like ZnO crystals. In addition, large-scale arrays of these ZnO crystals can be successfully synthesized onto various substrates such as amorphous glass, crystalline quartz, and PET. This implies this chemical method has a wide application in the fabrication of nano-/microscale devices.     

双酚A聚砜对PBT的结晶与多重熔化行为的影响

本文研究了PBT结晶的熔化行为及非晶性组分PSF的加入对PBT结晶度及熔化行为的影响。结果表明:PBT结晶熔化时的DSC双峰图为多重熔化行为而非多晶型的结果;PSF的加入对PBT结晶度影响不大,但对多重熔化行为有明显影响。此乃PSF无定形组分加入后,使PBT结晶速率减慢而形成更完善的PBT结晶之缘故。     

Metal-free synthesis of amphiphilic functional polycarbonates

Amphiphilic block copolymers of poly(5-benzyloxy trimethylene carbonate)(PBTMC) and poly(ethylene glycol)(PEG) were synthesized through enzymatic polymerization using immobilized porcine pancreas lipase(IPPL).The obtained copolymers with different compositions were characterized by GPC and ~1H NMR.The copolymer composition was in agreement with the feed ratio. The molecular weight of the copolymers showed an increasing trend with the decrease of PEG contents.Micelles of the copolymers were formed by dialysis procedure,and characterized by transmission electron microscopy (TEM).     

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.     

Enantioselective Friedel-Crafts type addition of indoles to nitro-olefins using a chiral hydrogen-bonding catalyst--synthesis of optically active tetrahydro-beta-carbolines

The enantioselective Friedel-Crafts addition of indoles to nitro-olefins using chiral hydrogen-bonding bis-sulfonamides as the catalysts has been developed. The reactions, in the presence of only 2 mol% catalyst, generally proceed in high yields and with enantioselectivities up to 64% ee, and the enantiomeric excess can be improved to >98% ee by recrystallization. Various synthetic transformations of the Friedel-Crafts adducts are demonstrated: the nitro group can easily be reduced to the corresponding amine and the product obtained can undergo a stereocontrolled Pictet-Spengler cyclization to give, for example, enantiopure tetrahydro-beta-carbolines. The X-ray structure of the chiral bis-sulfonamides has been determined and based on these structures the mechanism for the stereoselectivity in the reaction is discussed.