Copper‐Promoted Sandmeyer Difluoromethylthiolation of Aryl and Heteroaryl Diazonium Salts

An efficient copper‐promoted difluoromethylthiolation of aryl and heteroaryl diazonium salts is described. The reaction is conducted under mild reaction conditions and various functional groups were compatible. In addition, reactions of heteroaryl diazonium salts such as pyridyl, quinolinyl, benzothiazolyl, thiophenyl, carbazolyl, and pyrazolyl diazonium salts occurred smoothly to afford the medicinally important difluoromethylthiolated heteroarenes. Furthermore, a more practical one‐pot direct diazotization and difluoromethylthiolation protocol was developed, and it converts the aniline derivatives into difluoromethylthiolated arenes. The utility of the method is demonstrated by difluoromethylthiolation of a number of natural products and drug molecules.     

全氟辛胺修饰石墨烯复合材料的制备、表征及其疏水性能

通过化学法改性石墨烯,用全氟辛胺(FOA)的胺基与氧化石墨烯（GO）的羧基或烷氧基反应制备了含氟石墨烯复合材料（FOA-RGO）,用傅里叶红外光谱、热失重分析、拉曼光谱、高分辨透射电子显微镜（HRTEM）以及原子力显微镜（AFM）对复合材料的结构与形貌进行了表征。 结果表明,FOA已经成功地修饰到石墨烯的边缘。与未修饰的石墨烯相比,水滴在FOA-RGO表面上的接触角从68°提高至118°,显示出良好的疏水性能。     

聚苯胺共价修饰的氧化石墨烯的合成及其光限幅性能

利用酰胺化反应将聚苯胺(PANI)共价接枝到氧化石墨烯(GO)的表面,得到的杂化材料GO-PANI能很好地分散在常见的有机溶剂中。样品的XPS谱和红外光谱数据证实了在GO和PANI之间存在酰胺键。在316nm激光激发下,PANI和GO-PANI分别在420nm和416nm处显示出很强的荧光峰。GO-PANI的最大发射峰相对于PANI的发射峰蓝移了4nm,且荧光强度增强。开孔Z-扫描实验结果表明:与PANI相比,GO和PANI的共价键合使材料在532nm激光辐照下表现出更大的非线性消光系数和三阶非线性极化率虚部值,光限幅性能明显增强。     

Chemically Modified Graphene: The Influence of Structural Properties on the Assessment of Antioxidant Capacity

Graphene materials obtained by different synthetic routes possess dissimilar amount of defects and surface functionalities, which can influence their electrochemical performance towards the detection of electroactive probes. Oxygen‐containing groups can be either detrimental to the heterogeneous charge transfer or promote favorable interactions between the graphene surface and the analyte of interest, depending on the structure of the latter. Here, we compared three chemically modified graphenes, obtained by various procedures and carrying different amounts of oxygen functionalities, for the detection of standard gallic acid, a compound commonly used as an index of the antioxidant capacity of food and beverages. We found that electrochemically reduced graphene provided the best electrochemical performance in terms of calibration sensitivity, selectivity, and linearity of response. Our findings are important in order to understand the suitability of graphene platforms for the assessment of food quality.     

Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

Field‐grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi‐conducting or conducting particles. Here, polymer‐grafted reduced graphene oxide (rGO) is used as a filler to accomplish percolated networks at very low filling ratios (<2 vol.%) in a semi‐crystalline polymer matrix: poly(ethylene‐co‐butyl acrylate) (EBA). Various simulation models are used to predict the percolation threshold and the flake‐to‐flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is observed after surface modification, either by silanization or subsequent polymerizations. The non‐linear DC resistivity of neat and silanized rGO and its trapping of charge‐carriers in semi‐crystalline EBA are demonstrated for the first time. It is shown that the polymer‐grafted rGO improve the dispersibility in the EBA‐matrix and that the graft length controls the inter‐flake distances (i.e. charge‐carrier hopping distances). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm^‐1 and FGMs with a large and distinct drop in resistivity (six decades) are obtained, followed by saturation. The nonlinear drop in resistivity is attributed to narrow inter‐flake distance distributions of grafted rGO.     

Controlling the Degree of Functionalization: In-Depth Quantification and Side-Product Analysis of Diazonium Chemistry on SWCNTs

We present an in-depth qualitative and quantitative analysis of a reaction between 4-iodobenzenediazonium tetrafluoroborate and single-walled carbon nanotubes (SWCNTs) via thermogravimetric analysis coupled with mass spectrometry (TG-MS) or a gas chromatography and mass spectrometry (TG-GC-MS) as well as Raman spectroscopy. We propose a method for precise determination of the degree of functionalization and quantification of physisorbed aromates, detaching around their boiling point, alongside covalently bonded ones (cleavage over 200 °C). While the presence of some side products like phenol- or biphenyl species could be excluded, residual surfactant and minor amounts of benzene could be identified. A concentration-dependent experiment shows that the degree of functionalization increases with the logarithm of the concentration of applied diazonium salt, which can be exploited to precisely adjust the amount of aryl addends on the nanotube sidewall, up to 1 moiety per 100 carbon atoms.     

Room‐Temperature,Ligand‐ and Base‐Free Heck Reactions of Aryl Diazonium Salts at Low Palladium Loading: Sustainable Preparation of Substituted Stilbene Derivatives

The Pd(OAc)₂‐catalyzed Heck reaction of aryl diazonium salts with 2‐arylacrylates led to cis‐stilbenes with good to excellent stereoselectivity. The environmentally friendly protocol developed in this work features low palladium loading in technical‐grade methanol at room temperature under base‐, additive‐, and ligand‐free conditions. The same protocol applied to simple Heck coupling of aryl diazonium salts with methyl acrylate allows astonishingly low palladium loading, down to 0.005 mol %. The stereoselectivity experimentally observed for the synthesis of cis‐stilbenes has been rationalized by DFT calculations. Moreover, the role of methanol in promoting the reaction has been clarified by a computational study.     

衬底上石墨烯制备及改性研究

大面积高质量石墨烯的制备对石墨烯电子特性及石墨烯基纳器件相关研究有重要意义。本文综述了近几年来衬底上制备石墨烯的相关实验以及衬底与石墨烯相互作用研究的重要进展。目前,采用化学气相沉积、外延生长等方法可在衬底表面上制备出较大面积、高质量的石墨烯材料。衬底与石墨烯相互作用和界面间晶格匹配、原子成键及电荷转移等密切相关,其对吸附石墨烯的几何结构、能带结构及电子特性等产生明显影响。实验与理论计算的结合可望加深衬底与石墨烯作用机理的理解,指导衬底上石墨烯制备及改性的进一步研究。     

SiC衬底上石墨烯的性质、改性及应用研究

大面积高质量石墨烯的制备及其改性对于纳电子器件相关研究有重要意义. 本文综述了近年来SiC衬底上石墨烯的相关研究, 包括外延法制备石墨烯、石墨烯与SiC衬底的作用机理、SiC衬底上石墨烯的改性方法以及外延石墨烯在器件等方面应用的重要进展. 目前, 外延法的工艺较为成熟且制备的较大面积石墨烯品质较好. SiC衬底和石墨烯之间的相互作用与衬底的表面原子种类、表面态、原子成键、钝化程度、电荷转移等密切相关, 其对石墨烯的电子能带、载流子种类产生明显影响. 实验与理论计算的结合可望加深对SiC衬底与石墨烯作用机理的理解, 并指导外延石墨烯改性及其在器件应用方面的进一步研究.     

Proton Conductivities of Graphene Oxide Nanosheets: Single,Multilayer, and Modified Nanosheets

Proton conductivities of layered solid electrolytes can be improved by minimizing strain along the conduction path. It is shown that the conductivities (σ) of multilayer graphene oxide (GO) films (assembled by the drop‐cast method) are larger than those of single‐layer GO (prepared by either the drop‐cast or the Langmuir‐Blodgett (LB) method). At 60 % relative humidity (RH), the σ value increases from 1×10^?6 S cm^?1 in single‐layer GO to 1×10^?4 and 4×10^?4 S cm^?1 for 60 and 200 nm thick multilayer films, respectively. A sudden decrease in conductivity was observed for with ethylenediamine (EDA) modified GO (enGO), which is due to the blocking of epoxy groups. This experiment confirmed that the epoxide groups are the major contributor to the efficient proton transport. Because of a gradual improvement of the conduction path and an increase in the water content, σ values increase with the thickness of the multilayer films. The reported methods might be applicable to the optimization of the proton conductivity in other layered solid electrolytes.     

The Influence of Dimensional Effects on the Composition and Properties of Polydicarbonfluoride

The influence of dimensional effects on the compositions and properties of polydicarbonfluoride (C₂F)_n prepared from multilayered graphenes was investigated. Multilayered graphenes were produced by destructive thermal decomposition of intercalation compounds of “idealized” (C₂F)_n that were obtained by reaction of gaseous ClF₃ with natural graphite at a room temperature. The precursors of multilayered graphenes have a common formula (C₂F?xR)_n where R is an organic or inorganic component. It was shown that polydicarbonfluoride prepared from multilayered graphene does not form stable intercalation compound with ClF₃, in contrast to polydicarbonfluoride prepared from graphite, that forms its intercalation compound with ClF₃ during fluorination of initial graphite in the ClF₃ excess. Investigations of polydicarbonfluoride prepared from multilayered graphene showed that it cannot form intercalation compounds with different classes of organic and inorganic compounds as polydicarbonfluoride prepared from graphite can do. The absence of such intercalation activity for polydicarbonfluoride prepared from multilayered graphene can be explained by high exfoliation degree of multilayered graphene (3–4 nm) along the c‐axis that results in the presence of two‐dimensional (2D) structure properties in multilayered graphene. Dimensional effects transformed the chemical properties of polydicarbonfluoride prepared from multilayered graphene and lowered its decomposition temperature by 150 K in comparison with polydicarbonfluoride prepared from graphite.     

Chemical Modification of Graphene Oxide through Diazonium Chemistry and Its Influence on the Structure–Property Relationships of Graphene Oxide–Iron Oxide Nanocomposites

4‐Carboxyphenyl groups are covalently grafted onto graphene oxide via diazonium chemistry for studying their role on the adsorption of iron oxide nanoparticles. The nanoparticles are deposited via a novel phase‐transfer approach involving specific interactions at the interface between two immiscible solvents. The increased density and the homogeneous distribution of surface carboxyl moieties enable the preparation of a nanocomposite with improved iron oxide distribution and loading. Structure‐properties relationships are investigated by analysing the electrochemical properties of the nanocomposites, which are regarded as promising active materials for application in supercapacitors. It is demonstrated that the nature of the interactions between the components similarly affects the overall electrochemical performances of the nanocomposites and the structure of the materials.     

季铵盐改性氧化石墨烯的制备及其性能研究

本论文采用改进的Hummers法制备了氧化石墨烯(GO),并将氧化石墨烯用十二烷基二甲基苄基氯化铵(1227)进行修饰,得到1227非共价改性的氧化石墨烯(GO-1227)。用拉曼光谱、漫反射红外光谱分析、X-射线光电子表面能谱技术表征了其化学结构;用X-射线衍射分析、扫描电子显微镜与透射电子显微镜观察了其剥离情况和微观形貌;分析了它们在不同溶剂中的分散性。结果表明,季铵盐改性后,1227阳离子通过静电作用插入到GO片层之间,使GO片层进一步剥离,且在极性较弱的有机溶剂中的溶解性增加。热失重分析表明,GO-1227的初始分解温度提高了约70℃。将GO-1227与聚甲基丙烯酸甲酯与苯乙烯的嵌段共聚物(PMMA-b-PS)凝胶聚电解质复合,制备了纳米复合凝胶聚合物电解质(NGPE),并用交流阻抗法测试其电性能,发现占聚电解质总质量2‰的GO-1227可以将其离子电导率提高8.6倍。     

In Situ Synthesis and Characterization of Poly(aryleneethynylene)‐Grafted Reduced Graphene Oxide

Using highly soluble bromo‐functionalized reduced graphene oxide (RGBr) as a key graphene template for surface‐directing Sonogashira–Hagihara polymerization, a novel soluble poly(arylene‐ethynylene)‐grafted reduced graphene oxide, hereafter abbreviated as PAE‐g‐RGO, was prepared in situ. The entirely different electron distribution of LUMO and HOMO of PAE‐g‐RGO suggested the existence of a charge‐transfer (CT) state (PAE^.?–RGO^.+). The negative ΔG_CS value (?2.57 eV) indicates that the occurrence of the charge separation via ¹RGO* in o‐DCB is exothermic and favorable. Upon irradiation with 365 nm light, the light‐induced electron paramagnetic resonance (LEPR) spectrum of PAE‐g‐RGO showed a decrease in the spin‐state density owing to photoinduced intramolecular electron transfer events in this system. A sandwich‐type Al/PAE‐g‐RGO/ITO device showed representative bistable electrical switching behavior. The nonvolatile memory performance was attributed to the CT‐induced conductance changes, which was supported by molecular computation results and conductive atomic force microscopy (C‐AFM) images.     

Highly Efficient and Reversible Covalent Patterning of Graphene: 2D‐Management of Chemical Information

Patterned graphene‐functionalization with a tunable degree of functionalization can tailor the properties of graphene. Here, we present a new reductive functionalization approach combined with lithography rendering patterned graphene‐functionalization easily accessible. Two types of covalent patterning of graphene were prepared and their structures were unambiguously characterized by statistical Raman spectroscopy together with scanning electron microscopy/energy‐dispersive X‐ray spectroscopy (SEM‐EDS). The reversible defunctionalization processes, as revealed by temperature‐dependent Raman spectroscopy, enable the possibility to accurately modulate the degree of functionalization by annealing. This allows for the management of chemical information through complete write/store/erase cycles. Based on our strategy, controllable and efficient patterning graphene‐functionalization is no longer a challenge and facilitates the development of graphene‐based devices.     

Photophysical and Electrochemical Studies of Anchored Chromium (III) Complex on Reduced Graphene Oxide via Diazonium Chemistry

Covalently anchored chromium complex on reduced graphene oxide (rGO‐Cr) is successfully synthesised through trimethoxy silyl propanamine (TMSPA) and phenyl azo salicylaldehyde (PAS) coupling. The rGO‐Cr is characterised by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), electron dispersive analysis of X‐rays (EDAX), Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Absorption and emission properties of rGO‐TMSPA‐PAS are studied by excitation dependent photoluminescence emissions at room temperature. Electrochemical sensing activity of rGO‐Cr is monitored for paracetamol using modified glassy carbon electrode. Cyclic voltammetry measurements indicated that rGO‐Cr substantially enhance the eletrochemical response of paracetamol. The experimental factors are investigated and optimized.     

9,9‐Dimethylxanthene Derivatives with Room‐Temperature Phosphorescence: Substituent Effects and Emissive Properties

Room‐temperature phosphorescence (RTP) emitters with ultralong lifetimes are emerging as attractive targets because of their potential applications in bioimaging, security, and other areas. But their development is limited by ambiguous mechanisms and poor understanding of the correlation of the molecular structure and RTP properties. Herein, different substituents on the 9,9‐dimethylxanthene core (XCO) result in compounds with RTP lifetimes ranging from 52 to 601 ms, which are tunable by intermolecular interactions and molecular configurations. XCO‐PiCl shows the most persistent RTP because of its reduced steric bulk and multiple sites of the 1‐chloro‐2‐methylpropan‐2‐yl (PiCl) moiety for forming intermolecular interactions in the aggregated state. The substituent effects reported provide an efficient molecular design of organic RTP materials and establishes relationships among molecular structures, intermolecular interactions, and RTP properties.     

有机硅改性聚氨酯的合成与性能

在无溶剂条件下利用二步法合成了一系列氨基硅油改性聚氨酯,采用红外光谱对预聚体进行了表征,同时测试了材料的力学性能、耐热性、表面水接触角及微观形态,结果表明,改性后的聚氨酯具有优良的力学性能、耐热性及表面疏水性,且材料呈微观相分离形态。