共查询到20条相似文献,搜索用时 406 毫秒
1.
Dr. Yoshikazu Ito Dr. Yoichi Tanabe Dr. H.‐J. Qiu Dr. Katsuaki Sugawara Dr. Satoshi Heguri Dr. Ngoc Han Tu Dr. Khuong Kim Huynh Dr. Takeshi Fujita Prof. Takashi Takahashi Prof. Katsumi Tanigaki Prof. Mingwei Chen 《Angewandte Chemie (International ed. in English)》2014,53(19):4822-4826
We report three‐dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore‐size dependence, together with unique angular independence. The free‐standing, large‐scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices. 相似文献
2.
Photoinduced electron-transfer processes along molecular wires based on phenylenevinylene oligomers: a quantum-chemical insight 总被引:1,自引:0,他引:1
Pourtois G Beljonne D Cornil J Ratner MA Brédas JL 《Journal of the American Chemical Society》2002,124(16):4436-4447
Quantum-chemical techniques are applied to model the mechanisms of photoinduced charge transfer from a pi-electron donating group (tetracene, D) to a pi-electron-acceptor moiety (pyromellitimide, A) separated by a bridge of increasing size (p-phenylenevinylene oligomers, B). Correlated Hartree-Fock semiempirical approaches are exploited to calculate the four main parameters controlling the transfer rate (k(RP)) in the framework of Marcus-Jortner-Levich's formalism: (i) the electronic coupling between the initial and final states; (ii) and (iii) the internal and external reorganization energy terms; and (iv) the variation of the free Gibbs energy. The charge transfer is shown to proceed in these compounds through two competing mechanisms, coherent (superexchange) versus incoherent (bridge-mediated) pathways. While superexchange is the dominant mechanism for short bridges, incoherent transfer through hopping along the phenylene vinylene segment takes over in longer chains (for ca. three phenylenevinylene repeat units). The influence of the chemical structure of the pi-conjugated phenylenevinylene bridge on the electronic properties and the rate of charge transfer is also investigated. 相似文献
3.
S. Olszewski M. Baszczak T. Kwiatkowski 《International journal of quantum chemistry》2000,80(1):61-78
The changes of electron density due to the presence of a localized impurity in a crystal lattice are examined in dependence on the lattice dimensionality. The Koster–Slater impurity model developed for the case of a three‐dimensional simple cubic lattice has been taken as the basis of examinations. Ordinary bound states, virtual bound states, and delocalized electron states are considered in each lattice case. For the delocalized states extended in a one‐dimensional lattice the amplitude of the oscillatory changes of the electron density due to the impurity perturbation does not decrease with the distance from the impurity position, whereas for a two‐dimensional lattice this amplitude decreases roughly proportionally to the reciprocal value of the square root of the distance from the impurity. Let us note that a well‐known amplitude characterizing the decrease of the oscillatory change of the electron density in a three‐dimensional system is proportional to the reciprocal value of the third power of the distance from the impurity position. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 61–78, 2000 相似文献
4.
Wiberg J Guo L Pettersson K Nilsson D Ljungdahl T Mårtensson J Albinsson B 《Journal of the American Chemical Society》2007,129(1):155-163
Optimizing the ratio of the rates for charge separation (CS) over charge recombination (CR) is crucial to create long-lived charge-separated states. Mastering the factors that govern the electron transfer (ET) rates is essential when trying to achieve molecular-scale electronics, artificial photosynthesis, and also for the further development of solar cells. Much work has been put into the question of how the donor-acceptor distances and donor-bridge energy gaps affect the electronic coupling, V(DA), and thus the rates of ET. We present here a unique comparison on how these factors differently influence the rates for CS and CR in a porphyrin-based donor-bridge-acceptor model system. Our system contains three series, each of which focuses on a separate charge-transfer rate-determining factor, the donor-acceptor distance, the donor-bridge energy gap, and last, the influence of the electron acceptor on the rate for charge transfer. In these three series both CS and CR are governed by superexchange interactions which make a CR/CS comparative study ideal. We show here that the exponential distance dependence increases slightly for CR compared to that for CS as a result of the increased tunneling barrier height for this reaction, in accordance with the McConnell superexchange model. We also show that the dependence on the tunneling barrier height is different for CS and CR. This difference is highly dependent on the electron acceptor and thus cannot solely be explained by the differences in the frontier orbitals of the electron donor in these porphyrin systems. 相似文献
5.
Tuning the Electronic Coupling and Electron Transfer in Mo2 Donor–Acceptor Systems by Variation of the Bridge Conformation
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mei Ting Kang Miao Meng Ying Ning Tan Tao Cheng Prof. Chun Y. Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3115-3126
Assembling two quadruply bonded dimolybdenum units [Mo2(DAniF)3]+ (DAniF=N,N′‐di(p‐anisyl)formamidinate) with 1,4‐naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2(DAniF)3}2(μ‐1,4‐O2CC10H6CO2)], [{Mo2(DAniF)3}2(μ‐1,4‐OSCC10H6COS)], and [{Mo2(DAniF)3}2(μ‐1,4‐S2CC10H6CS2)]. In the X‐ray structures, the naphthalene bridge deviates from the plane defined by the two Mo?Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed‐valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab=258–345 cm?1) are lowered by a factor of two or more, and the electron‐transfer rate constants (ket≈1011 s?1) are reduced by about one order of magnitude. These results show that, when the electron‐transporting ability of the bridge and electron‐donating (electron‐accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO–LUMO energy gap by elevating the (bridging) ligand‐based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer. 相似文献
6.
Exploring the Electronic Structure of an Organic Semiconductor Based on a Compactly Fused Electron Donor–Acceptor Molecule
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Pere Alemany Prof. Enric Canadell Dr. Yan Geng Dr. Jürg Hauser Dr. Piero Macchi Dr. Karl Krämer Prof. Silvio Decurtins Dr. Shi‐Xia Liu 《Chemphyschem》2015,16(7):1361-1365
A Mott‐type semiconductor based on a compactly fused and partially oxidized electron donor–acceptor (D–A) molecule was recently prepared and identified to exhibit a large room‐temperature conductivity of 2 S cm?1. In a marked contrast to the organic conductors characterized by relatively well decoupled and segregated uniform stacks of D and A moieties, the formally half‐oxidized tetrathiafulvalene donors of the actual compound are organized in columnar π stacks only, whereby the coplanar electron‐acceptor units, namely benzothiadiazole, are closely annulated along their ridges. Herein, we present a theoretical study that explores the electronic structure of this novel type of organic semiconductor. The highly symmetric‐solid state material behaves as a one‐dimensional electronic system with strong antiferromagnetic interactions (coupling constant>200 cm?1). The unique shape and local dipole of this redox‐active fused electron D–A molecule lays the basis for further investigations of the collective electronic structure, mainly in the function of different counterions embedded in the crystalline lattice. 相似文献
7.
Highly Active Bidirectional Electron Transfer by a Self‐Assembled Electroactive Reduced‐Graphene‐Oxide‐Hybridized Biofilm
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Yang‐Chun Yong Yang‐Yang Yu Prof. Xinhai Zhang Prof. Hao Song 《Angewandte Chemie (International ed. in English)》2014,53(17):4480-4483
Low extracellular electron transfer performance is often a bottleneck in developing high‐performance bioelectrochemical systems. Herein, we show that the self‐assembly of graphene oxide and Shewanella oneidensis MR‐1 formed an electroactive, reduced‐graphene‐oxide‐hybridized, three‐dimensional macroporous biofilm, which enabled highly efficient bidirectional electron transfers between Shewanella and electrodes owing to high biomass incorporation and enhanced direct contact‐based extracellular electron transfer. This 3D electroactive biofilm delivered a 25‐fold increase in the outward current (oxidation current, electron flux from bacteria to electrodes) and 74‐fold increase in the inward current (reduction current, electron flux from electrodes to bacteria) over that of the naturally occurring biofilms. 相似文献
8.
Beatriz Pelado Dr. Fawzi Abou‐Chahine Joaquín Calbo Dr. Rubén Caballero Dr. Pilar de la Cruz Dr. José M. Junquera‐Hernández Prof. Enrique Ortí Prof. Nikolai V. Tkachenko Prof. Fernando Langa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5814-5825
The role of π‐conjugated molecular bridges in through‐space and through‐bond electron transfer is studied by comparing two porphyrin–fullerene donor–acceptor (D–A) dyads. One dyad, ZnP–Ph–C60 (ZnP=zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP–EDOTV–C60, introduces an additional 3,4‐ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge‐separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP–Ph–C60 dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D–A bridge. 相似文献
9.
Tidjani Ngadi 《International journal of quantum chemistry》2000,78(4):206-211
We reconsider, in this work, the construction of the two‐dimensional (2‐D) periodic table. The two‐dimensional logarithmic Coulomb system is used to generate atomic shells for the 2‐D atoms. A q‐deformed model is developed to explain the ordering of the shells predicted by the 2‐D Madelung rule. Our model, with the value q=1.26 for the deformation parameter, reproduce very well the above rule. We also compute the key function and the address function which, together with our model for the Madelung rule, permit us to give a new format of the 2‐D periodic table. It is shown that this table is different from the one existing in the literature, and we have a new family of elements, the g family. The question of the existence of 2‐D “ions” is briefly discussed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 206–211, 2000 相似文献
10.
Amlan K. Roy 《International journal of quantum chemistry》2008,108(5):837-847
Exploratory variational pseudopotential density functional calculations are performed for the electronic properties of many‐electron systems in the 3D cartesian coordinate grid (CCG). The atom‐centered localized gaussian basis set, electronic density, and the two‐body potentials are set up in the 3D cubic box. The classical Hartree potential is calculated accurately and efficiently through a Fourier convolution technique. As a first step, simple local density functionals of homogeneous electron gas are used for the exchange‐correlation potential, while Hay‐Wadt‐type effective core potentials are employed to eliminate the core electrons. No auxiliary basis set is invoked. Preliminary illustrative calculations on total energies, individual energy components, eigenvalues, potential energy curves, ionization energies, and atomization energies of a set of 12 molecules show excellent agreement with the corresponding reference values of atom‐centered grid as well as the grid‐free calculation. Results for three atoms are also given. Combination of CCG and the convolution procedure used for classical Coulomb potential can provide reasonably accurate and reliable results for many‐electron systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
11.
A series of [2.2]paracylophane-bridged bis-triarylamine mixed-valence (MV) radical cations were analyzed by a generalized Mulliken-Hush (GMH) three-level model which takes two transitions into account: the intervalence charge transfer (IV-CT) band which is assigned to an optically induced hole transfer (HT) from one triarylamine unit to the second one and a second band associated with a triarylamine radical cation to bridge (in particular, the [2.2]paracyclophane bridge) hole transfer. From the GMH analysis, we conclude that the [2.2]paracyclophane moiety is not the limiting factor which governs the intramolecular charge transfer. AM1-CISD calculations reveal that both through-bond as well as through-space interactions of the [2.2]paracyclophane bridge play an important role for hole transfer processes. These electronic interactions are of course smaller than direct pi-conjugation, but from the order of magnitude of the couplings of the [2.2]paracyclophane MV species, we assume that this bridge is able to mediate significant through-space and through-bond interactions and that the cyclophane bridge acts more like an unsaturated spacer rather than a saturated one. From the exponential dependence of the electronic coupling V between the two triarylamine localized states on the distance r between the two redox centers, we infer that the hole transfer occurs via a superexchange mechanism. Our analysis reveals that even significantly longer pi-conjugated bridges should still mediate significant electronic interactions because the decay constant beta of a series of pi-conjugated MV species is small. 相似文献
12.
Yannan Zhou Qun Xu Tianpei Ge Xiaoli Zheng Li Zhang Pengfei Yan 《Angewandte Chemie (International ed. in English)》2020,59(8):3322-3328
In two‐dimensional (2D) amorphous nanosheets, the electron–phonon coupling triggered by localization of the electronic state as well as multiple‐scattering feature make it exhibit excellent performance in optical science. VS2 nanosheets, especially single‐layer nanosheets with controllable electronic structure and intrinsic optical properties, have rarely been reported owing to the limited preparation methods. Now, a controllable and feasible switching method is used to fabricate 2D amorphous VS2 and partial crystallized 2D VO2(D) nanosheets by altering the pressure and temperature of supercritical CO2 precisely. Thanks to the strong carrier localization and the quantum confinement, the unique 2D amorphous structures exhibit full band absorption, strong photoluminescence, and outstanding photothermal conversion efficiency. 相似文献
13.
Justifications developed for the application the free electron model to the π‐orbitals of conjugated molecules suggest that the optical properties of these molecules would be well described by a one‐dimensional free electron model with a potential chosen to reproduce the energy level spacing of the ground state occupied π‐orbitals. Such a hybrid ab initio/free electron modeling approach, where the free electron potential parameters are optimized on a molecule‐by‐molecule basis, is developed, and applied to a series of simple cyanine and oxonol dyes. The ensuing predictions for λmax, oscillator strengths, and redox properties compare well to available experimental information. Two important strengths of this approach are that no explicit calculations of the excited electronic state are required, and that the ab initio determination of the occupied π‐orbital level spacing considers all the electrons (π and σ) of the entire molecule in a specified geometry, environment, etc. This second characteristic gives the ability to efficiently model modifications of the optical properties of conjugated molecules resulting from chemical and/or physical modifications occuring within and remote to the conjugated region of the molecule. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 943–953, 2000 相似文献
14.
Dr. Jordi Poater Prof. Dr. Miquel Solà Prof. Dr. Clara Viñas Prof. Dr. Francesc Teixidor 《Angewandte Chemie (International ed. in English)》2014,53(45):12191-12195
A bridge between classical organic polycyclic aromatic hydrocarbons (PAH) and closo borohydride clusters is established by showing that they share a common origin regulated by the number of valence electrons in an electronic confined space. Application of the proposed electronic confined space analogy (ECSA) method to archetypal PAHs leads to the conclusion that the 4n+2 Wade–Mingos rule for three‐dimensional closo boranes is equivalent to the (4n+2)π Hückel rule for two‐dimensional PAHs. More importantly, use of ECSA allows design of new interesting fused closo boranes which can be a source of inspiration for synthetic chemists. 相似文献
15.
Dr. Lok Kumar Shrestha Dr. Rekha Goswami Shrestha Prof. Yusuke Yamauchi Dr. Jonathan P. Hill Dr. Toshiyuki Nishimura Prof. Kun'ichi Miyazawa Prof. Takazumi Kawai Prof. Susumu Okada Dr. Katsunori Wakabayashi Prof. Katsuhiko Ariga 《Angewandte Chemie (International ed. in English)》2015,54(3):951-955
Here we report the thermal conversion of one‐dimensional (1D) fullerene (C60) single‐crystal nanorods and nanotubes to nanoporous carbon materials with retention of the initial 1D morphology. The 1D C60 crystals are heated directly at very high temperature (up to 2000 °C) in vacuum, yielding a new family of nanoporous carbons having π‐electron conjugation within the sp2‐carbon robust frameworks. These new nanoporous carbon materials show excellent electrochemical capacitance and superior sensing properties for aromatic compounds compared to commercial activated carbons. 相似文献
16.
Jordi Poater Miquel Sol Clara Vias Francesc Teixidor 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(45):12387-12391
A bridge between classical organic polycyclic aromatic hydrocarbons (PAH) and closo borohydride clusters is established by showing that they share a common origin regulated by the number of valence electrons in an electronic confined space. Application of the proposed electronic confined space analogy (ECSA) method to archetypal PAHs leads to the conclusion that the 4n+2 Wade–Mingos rule for three‐dimensional closo boranes is equivalent to the (4n+2)π Hückel rule for two‐dimensional PAHs. More importantly, use of ECSA allows design of new interesting fused closo boranes which can be a source of inspiration for synthetic chemists. 相似文献
17.
Tian‐Nan Ye Li‐Bing Lv Prof. Xin‐Hao Li Miao Xu Prof. Jie‐Sheng Chen 《Angewandte Chemie (International ed. in English)》2014,53(27):6905-6909
Effective integration of one‐dimensional carbon nanofibers (CNF) and two‐dimensional carbon sheets into three‐dimensional (3D) conductive frameworks is essential for their practical applications as electrode materials. Herein, a novel “vein‐leaf”‐type 3D complex of carbon nanofibers with nitrogen‐doped graphene (NG) was prepared through a simple thermal condensation of urea and bacterial cellulose. During the formation of the 3D complex CNF@NG, the graphene species was tethered to CNF via carbon–carbon bonds. Such an interconnected 3D network facilitates both the electron transfer and mass diffusion for electrochemical reactions. 相似文献
18.
Christina Schubert Dr. Mateusz Wielopolski Lars‐Hendrik Mewes Dr. Gustavo de Miguel Rojas Dr. Cornelia van der Pol Dr. Kathryn C. Moss Prof. Martin R. Bryce Prof. Jacques E. Moser Prof. Timothy Clark Prof. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7575-7586
A new series of donor–bridge–acceptor (D–B–A) compounds consisting of π‐conjugated oligofluorene (oFL) bridges between a ferrocene (Fc) electron‐donor and a fullerene (C60) electron‐acceptor have been synthesized. In addition to varying the length of the bridge (i.e., mono‐ and bi‐fluorene derivatives), four different ways of linking ferrocene to the bridge have been examined. The Fc moiety is linked to oFL: 1) directly without any spacer, 2) by an ethynyl linkage, 3) by a vinylene linkage, and 4) by a p‐phenylene unit. The electronic interactions between the electroactive species have been characterized by cyclic voltammetry, absorption, fluorescence, and transient absorption spectroscopy in combination with quantum chemical calculations. The calculations reveal exceptionally close energy‐matching between the Fc and the oFL units, which results in strong electronic‐coupling. Hence, intramolecular charge‐transfer may easily occur upon exciting either the oFLs or Fcs. Photoexcitation of Fc–oFL–C60 conjugates results in transient radical‐ion‐pair states. The mode of linkage of the Fc and FL bridge has a profound effect on the photophysical properties. Whereas intramolecular charge‐separation is found to occur rather independently of the distance, the linker between Fc and oFL acts (at least in oFL) as a bottleneck and significantly impacts the intramolecular charge‐separation rates, resulting in beta values between βCS 0.08 and 0.19 Å?1. In contrast, charge recombination depends strongly on the electron‐donor–acceptor distance, but not at all on the linker. A value of βCR (0.35±0.01 Å?1) was found for all the systems studied. Oligofluorenes prove, therefore, to be excellent bridges for probing how small structural variations affect charge transport in D–B–A systems. 相似文献
19.
Prof. Dr. Zhuhua Zhang Dr. Sharmila N. Shirodkar Dr. Yang Yang Prof. Dr. Boris I. Yakobson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(48):15623-15628
Boron nanostructures are easily charged but how charge carriers affect their structural stability is unknown. We combined cluster expansion methods with first‐principles calculations to analyze the dependence of the preferred structure of two‐dimensional (2D) boron, or “borophene”, on charge doping controlled by a gate voltage. At a reasonable doping level of 3.12×1014 cm−2, the hollow hexagon concentration in the ground state of 2D boron increases to 1/7 from 1/8 in its charge‐neutral state. The numerical result for the dependence of hollow hexagon concentration on the doping level is well described by an analytical method based on an electron‐counting rule. Aside from in‐plane electronic bonding, the hybridization among out‐of‐plane boron orbitals is crucial for determining the relative stability of different sheets at a given doping level. Our results offer new insight into the stability mechanism of 2D boron and open new ways for the control of the lattice structure during formation. 相似文献
20.
Transition from a Metal‐Localized Mixed‐Valence Compound to a Fully Delocalized and Bridge‐Biased Electrophore in a Ruthenium–Amine–Ruthenium Tricenter System
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jian‐Hong Tang Dr. Jiang‐Yang Shao Yan‐Qin He Dr. Si‐Hai Wu Prof. Jiannian Yao Prof. Yu‐Wu Zhong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10341-10345
A series of cyclometalated diruthenium complexes with a redox‐active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one‐electron‐oxidized state can be either in the form of a weakly or strongly coupled mixed‐valence diruthenium complex, a fully charge‐delocalized three‐center system, or a bridge‐biased electrophore. This transition among different electronic forms was supported by electrochemistry, near‐infrared absorption, electron paramagnetic resonance, and density functional theory analysis. 相似文献