Structure and Electron Transport at Metal Atomic Junctions Doped with Dichloroethylene

The front cover artwork was provided by the group of Prof. Nishino, Tokyo Institute of Technology. The image depicts the investigation of the structure and electron transport of the Au, Ag, Cu, Ni, Fe, and Pd atomic junctions doped with dichloroethylene. Read the full text of the Article at 10.1002/cphc.201900988 .     

金属/分子/金属结的电子输运机理与表征

金属/分子/金属结是分子电子学中的基本单元.根据电子的相位是否发生改变,分子结中的电子输运可以分为相干输运和非相干输运两类.在实验上,分子结的表征方法可以分为电学性质表征和非电学性质表征两类.本文借助能级图,首先对分子结的电子输运机理作了简明解释.在此基础上,结合文献报道和本课题组此前的工作,对分子结的一些常用电学表征方法,包括电流-电压特性曲线、电流-时间曲线、电导统计柱状图、转变电压谱、散粒噪声测试、非弹性电子隧道谱和热电效应法进行了介绍.     

Electron Transport and Redox Reactions in Molecular Electronic Junctions

Electron transport through single molecules or collections of molecules oriented in parallel can occur by several mechanisms, including coherent tunneling, activated transfer between potential wells, various “hopping” modes, etc. Given suitable energy levels and sufficiently long charge transport times, reduction or oxidation with accompanying nuclear reorganization can occur to generate “polarons”, that is, localized redox centers in the molecule or monolayer. Redox events in molecular junctions are amenable to spectroscopic monitoring in working devices, and can have major effects on the electronic behavior of the junction. Several examples are presented, along with a possible application to molecular memory.     

Molecular Wires in Single‐Molecule Junctions: Charge Transport and Vibrational Excitations

We investigate the effect of vibrations on the electronic transport through single‐molecule junctions, using the mechanically controlled break junction technique. The molecules under investigation are oligoyne chains with appropriate end groups, which represent both an ideally linear electrical wire and an ideal molecular vibrating string. Vibronic features can be detected as satellites to the electronic transitions, which are assigned to longitudinal modes of the string by comparison with density functional theory data.     

噻吩环取代掺杂一维共轭碳基材料的电子输运

一维共轭碳基材料以苯环为基本单元,具有优越的导电性,分子光电器件的发展要求其在高导电性的前提下兼具富电子或少电子特征.本工作设计了噻吩环取代掺杂一维共轭碳基材料的寡聚苯并[1,2-b：4,5-b']二噻吩（BmT）和寡聚噻吩（TnP）分子模型,利用密度泛函理论结合非平衡格林函数方法研究了掺杂位置和掺杂程度对其输运行为的影响.噻吩环在一维共轭碳基材料上的取代掺杂有效提升了材料的电子输运效率.BmT和TnP分子的导电特性随分子长度的变化表明分子的共轭程度决定了电子输运效率.反式BmT和TnP分子具有多条电子传输路径,而顺式BmT和TnP分子随着分子长度增加,经历了由单条电子传输路径至多条电子传输路径的转变.该研究结果为开发高性能碳基分子电子材料提供了重要参考.     

Iterative Atomic Charge Partitioning of Valence Electron Density

We propose an atomic charge partitioning scheme, iterative adjusted charge partitioning (I-ACP), belonging to the stockholder family and based on partitioning of the valence molecular electron density. The method uses a Slater-type weighting factor c_Ar^2n–2exp(–α_Ar), where α_A is a fixed parameter and c_A is determined iteratively. The parameters α_A were fitted for 17 main-group elements. The I-ACP scheme is shown to produce consistent, chemically meaningful atomic charges. Several stockholder-type charge-partitioning are compared. Extensive numerical tests demonstrate that in most cases, I-ACP surpasses most other methods by reproducing more accurately molecular dipole moments. © 2018 Wiley Periodicals, Inc.     

原子构造原理与过渡元素原子的价电子组态

众所周知,元素周期系过渡元素基态原子价电子组态的多样化是已往的原子构造理论无论是从定性还是从定量方面都是迄今难以给出圆满理论解释的原子构造现象之一^[1-11]。本文介绍新近提出的原子构造的对称性原理以及依据这一原理对上述原子构造现象所作的系统理论解释。     

碱金属修饰g-C3N4的能带结构调控与载流子迁移过程

采用平面波超软赝势方法研究了Li、Na、K三种碱金属离子修饰对g-C₃N₄能带结构和载流子迁移过程的影响。对建立的六种吸附构型分别采用广义梯度近似和局域密度近似进行计算,发现三种碱金属离子均更趋向于吸附在g-C₃N₄片层内的大空洞中央位置（F位置）。对于碱金属与g-C₃N₄形成的n型Schottky结,通过能带结构和功函数的计算,发现界面电荷的平衡使g-C₃N₄的能带电位分别整体下移1.52 V（Li）、1.07 V（Na）、0.86 V（K）。其中K离子的引入一方面将g-C₃N₄的价带和导带调整到更合适的氧化还原电位,另一方面增大了g-C₃N₄的最高占据轨道（HOMO）和最低未占据轨道（LOMO）的分布,有利于提高载流子的迁移率,同时出现的HOMO和LOMO轨道非共面特性有利于电子和空穴的分离。     

氟代位置对苝酰亚胺聚集态结构和电子传输性能的影响

合成了三种新型的有机电子受体: N,N'-二(2-氟代苯基)-3,4,9,10-苝四羧基二酰亚胺(D2MFPP)、N,N'-二(3-氟代苯基)-3,4,9,10-苝四羧基二酰亚胺(D3MFPP)和N,N'-二(4-氟代苯基)-3,4,9,10-苝四羧基二酰亚胺(D4MFPP). 利用元素分析、傅立叶变换红外(FTIR)等方法表征了它们的分子结构, 用紫外-可见光吸收光谱(UV-Vis)、X射线衍射(XRD)和原子力显微镜(AFM)等手段研究了氟代位置对苝酰亚胺薄膜聚集态结构的影响, 发现氟代使苝酰亚胺的聚集态发生变化, 且不同位置的氟代对其影响也不一样. 除了分子结构的影响, 外场条件也会产生很大的作用. 通过制备场效应晶体管研究了其电子传输性能, 发现氟代后器件的空气稳定性有明显提高.     

Origin of the Electron Transport Properties of Aromatic and Antiaromatic Single Molecule Circuits

Antiaromatic molecules have been predicted to exhibit increased electron transport properties when placed between two nanoelectrodes compared to their aromatic analogues. While some studies have demonstrated this relationship, others have found no substantial increase. We use atomistic simulations to establish a general relationship between the electronic spectra of aromatic, antiaromatic, and quinoidal molecules and illustrate its implications for electron transport. We compare the electronic properties of a series of aromatic-antiaromatic counterparts and show that antiaromaticity effectively p-dopes the aromatic electronic spectra. As a consequence, the conducting properties of aromatic-antiaromatic analogues are closely related. For similar attachment points to the electrodes, an interference feature is expected in the HOMO-LUMO gap of one whenever it is absent in the other one. We demonstrate how the relative conductance of aromatic-antiaromatic pairs can be tuned and even reversed through the choice of chemical linker groups. Our work provides a general picture relating connectivity, (anti)aromaticity, and quantum interference and establishes new design rules for single molecule circuits.     

The Diversity of Electron‐Transport Behaviors of Molecular Junctions: Correlation with the Electron‐Transport Pathway

We report the electron‐transport behaviors of a number of molecular junctions composed of π‐conjugated molecular wires. From calculations performed by using density functional theory (DFT) combined with the non‐equilibrium Green’s function (NEGF) method, we found that the length–conductivity relations are diverse, depending on the particular molecular structures. The results reveal that the conductance–length dependence follows an exponential law for many conjugated molecules with a single channel, such as oligothiophene, oligopyrrole and oligophenylene. Therefore, a quantitative relation between the energy gap (E_g)_∞ of the molecular wire and the attenuation factor β can be defined. However, when the molecular wires have multichannels, the decay of conductance does not follow the exponential relation. For example, the conductance of porphyrin‐based oligomers and fused thiophene decays almost linearly. The diversity of electron‐transport behaviors of molecular junctions is directly dominated by the electron‐transport pathway.     

染料敏化太阳电池中的电子传输及复合

电子传输与复合是染料敏化太阳电池中仍然存在争议的基本物理过程,解决这些争议对于进一步提高染料敏化太阳电池的光伏性能及稳定性是至关重要的。多缺陷理论模型用扩散系数及电子寿命这两个基本物理量准确地描述了染料敏化太阳电池中的电子传输及复合。为了对扩散系数及电子寿命等物理参数进行实验测量,近年来,人们发展出了频域、时域以及稳态等多种实验方法和技术手段,本文对这些方法进行了综述,并分别从纳晶半导体光阳极、电解质以及敏化染料等方面评述了近年来电子传输及复合的相关研究进展。     

“基于尺度再探原子结构”的教学设计与实施*

教学设计阶段首先进行原子结构学科理解研究,通过阐释如何基于原子核认识原子的构成,如何基于核外电子运动认识原子的结构这2个本原性问题,对主题大概念原子结构模型进行本原性、结构化地理解。继而从教学目标和教学思路设计、教学实施过程、学生收获、教师反思及专家评价等方面,系统地呈现了基于学科理解的“素养为本”“基于尺度再探原子结构”课堂教学的研究过程。     

Electron Transport through Single π‐Conjugated Molecules Bridging between Metal Electrodes

Understanding electron transport through a single molecule bridging between metal electrodes is a central issue in the field of molecular electronics. This review covers the fabrication and electron‐transport properties of single π‐conjugated molecule junctions, which include benzene, fullerene, and π‐stacked molecules. The metal/molecule interface plays a decisive role in determining the stability and conductivity of single‐molecule junctions. The effect of the metal–molecule contact on the conductance of the single π‐conjugated molecule junction is reviewed. The characterization of the single benzene molecule junction is also discussed using inelastic electron tunneling spectroscopy and shot noise. Finally, electron transport through the π‐stacked system using π‐stacked aromatic molecules enclosed within self‐assembled coordination cages is reviewed. The electron transport in the π‐stacked systems is found to be efficient at the single‐molecule level, thus providing insight into the design of conductive materials.     

Synthesis and Crystal Structure of A New Armed-tetraazacrown Ether and Its Liquid Membrane Transport of Alkali Metal Cations

Introduction　　Transportofcationsacrossanorganicliquidmem branewhichseparatestwowaterphaseshasbeenexten sivelyinvestigated .1Thesyntheticmacrocyclicligands ,suchascrownethers ,areusuallyusedasmodelcarrierstomimicthenaturallyoccurringantibioticmacrocycleswhichhavebeenshowntoalterthepermeabilityofbiologicalmembranestocertaincations .2 ,3 Thus ,theyhaveimpor tantapplicationsinbothchemistryandbiologytoselectivecomplexationofvariousmetalcations .4 ,5Itwasreportedthatthedivalenttransition metalcomp…     

Ferrocene‐Substituted Naphthalenediimide with Broad Absorption and Electron‐Transport Properties in the Segregated‐Stack Structure

A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens ( Fc‐NDI‐Fc ), was synthesized. The Fc units provide high crystallinity to Fc‐NDI‐Fc with good solubility to conventional organic solvents. The Fc units also work as electron‐donating substituents, in contrast to the electron‐deficient NDI unit, resulting in broad charge‐transfer absorption of Fc‐NDI‐Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc‐NDI‐Fc formed a segregated‐stack structure. The DFT calculation based on the crystal structure showed that the NDI π‐orbitals extended over two axes. The extended π‐network of the NDI units led to the electron‐transport properties of Fc‐NDI‐Fc , which was confirmed using a flash‐photolysis time‐resolved microwave conductivity technique.