Co-reporter:Cancan Huang, Alexander V. Rudnev, Wenjing Hong and Thomas Wandlowski
Chemical Society Reviews 2015 vol. 44(Issue 4) pp:889-901
Publication Date(Web):05 Jan 2015
DOI:10.1039/C4CS00242C
Molecular electronics aims to construct functional molecular devices at the single-molecule scale. One of the major challenges is to construct a single-molecule junction and to further manipulate the charge transport through the molecular junction. Break junction techniques, including STM break junctions and mechanically controllable break junctions are considered as testbed to investigate and control the charge transport on a single-molecule scale. Moreover, additional electrochemical gating provides a unique opportunity to manipulate the energy alignment and molecular redox processes for a single-molecule junction. In this review, we start from the technical aspects of the break junction technique, then discuss the molecular structure–conductance correlation derived from break junction studies, and, finally, emphasize electrochemical gating as a promising method for the functional molecular devices.
Co-reporter:Yan Geng; Sara Sangtarash; Cancan Huang; Hatef Sadeghi; Yongchun Fu; Wenjing Hong; Thomas Wandlowski; Silvio Decurtins; Colin J. Lambert;Shi-Xia Liu
Journal of the American Chemical Society 2015 Volume 137(Issue 13) pp:4469-4476
Publication Date(Web):March 17, 2015
DOI:10.1021/jacs.5b00335
Experiments using a mechanically controlled break junction and calculations based on density functional theory demonstrate a new magic ratio rule (MRR) that captures the contribution of connectivity to the electrical conductance of graphene-like aromatic molecules. When one electrode is connected to a site i and the other is connected to a site i′ of a particular molecule, we assign the molecule a “magic integer” Mii′. Two molecules with the same aromatic core but different pairs of electrode connection sites (i,i′ and j,j′, respectively) possess different magic integers Mii′ and Mjj′. On the basis of connectivity alone, we predict that when the coupling to electrodes is weak and the Fermi energy of the electrodes lies close to the center of the HOMO–LUMO gap, the ratio of their conductances is equal to (Mii′/Mjj′)2. The MRR is exact for a tight-binding representation of a molecule and a qualitative guide for real molecules.
Co-reporter:Sara Sangtarash; Cancan Huang; Hatef Sadeghi; Gleb Sorohhov; Jürg Hauser; Thomas Wandlowski; Wenjing Hong; Silvio Decurtins; Shi-Xia Liu;Colin J. Lambert
Journal of the American Chemical Society 2015 Volume 137(Issue 35) pp:11425-11431
Publication Date(Web):August 19, 2015
DOI:10.1021/jacs.5b06558
If quantum interference patterns in the hearts of polycyclic aromatic hydrocarbons could be isolated and manipulated, then a significant step toward realizing the potential of single-molecule electronics would be achieved. Here we demonstrate experimentally and theoretically that a simple, parameter-free, analytic theory of interference patterns evaluated at the mid-point of the HOMO–LUMO gap (referred to as M-functions) correctly predicts conductance ratios of molecules with pyrene, naphthalene, anthracene, anthanthrene, or azulene hearts. M-functions provide new design strategies for identifying molecules with phase-coherent logic functions and enhancing the sensitivity of molecular-scale interferometers.
Co-reporter:Dr. Yonghai Li;Masoud Baghernejad;Al-Galiby Qusiy;Dr. David ZsoltManrique;Dr. Guanxin Zhang;Joseph Hamill;Dr. Yongchun Fu;Dr. Peter Broekmann;Dr. Wenjing Hong;Dr. Thomas Wlowski;Dr. Deqing Zhang;Dr. Colin Lambert
Angewandte Chemie International Edition 2015 Volume 54( Issue 46) pp:13586-13589
Publication Date(Web):
DOI:10.1002/anie.201506458
Abstract
We studied charge transport through core-substituted naphthalenediimide (NDI) single-molecule junctions using the electrochemical STM-based break-junction technique in combination with DFT calculations. Conductance switching among three well-defined states was demonstrated by electrochemically controlling the redox state of the pendent diimide unit of the molecule in an ionic liquid. The electrical conductances of the dianion and neutral states differ by more than one order of magnitude. The potential-dependence of the charge-transport characteristics of the NDI molecules was confirmed by DFT calculations, which account for electrochemical double-layer effects on the conductance of the NDI junctions. This study suggests that integration of a pendant redox unit with strong coupling to a molecular backbone enables the tuning of charge transport through single-molecule devices by controlling their redox states.
Co-reporter:Cancan Huang;Dr. Songjie Chen;Kristian BaruëlØrnsø;David Reber;Masoud Baghernejad;Dr. Yongchun Fu; Thomas Wlowski; Silvio Decurtins;Dr. Wenjing Hong; Kristian Sommer Thygesen;Dr. Shi-Xia Liu
Angewandte Chemie International Edition 2015 Volume 54( Issue 48) pp:14304-14307
Publication Date(Web):
DOI:10.1002/anie.201506026
Abstract
Tuning charge transport at the single-molecule level plays a crucial role in the construction of molecular electronic devices. Introduced herein is a promising and operationally simple approach to tune two distinct charge-transport pathways through a cruciform molecule. Upon in situ cleavage of triisopropylsilyl groups, complete conversion from one junction type to another is achieved with a conductance increase by more than one order of magnitude, and it is consistent with predictions from ab initio transport calculations. Although molecules are well known to conduct through different orbitals (either HOMO or LUMO), the present study represents the first experimental realization of switching between HOMO- and LUMO-dominated transport within the same molecule.
Co-reporter:Dr. Yonghai Li;Masoud Baghernejad;Al-Galiby Qusiy;Dr. David ZsoltManrique;Dr. Guanxin Zhang;Joseph Hamill;Dr. Yongchun Fu;Dr. Peter Broekmann;Dr. Wenjing Hong;Dr. Thomas Wlowski;Dr. Deqing Zhang;Dr. Colin Lambert
Angewandte Chemie 2015 Volume 127( Issue 46) pp:13790-13793
Publication Date(Web):
DOI:10.1002/ange.201506458
Abstract
We studied charge transport through core-substituted naphthalenediimide (NDI) single-molecule junctions using the electrochemical STM-based break-junction technique in combination with DFT calculations. Conductance switching among three well-defined states was demonstrated by electrochemically controlling the redox state of the pendent diimide unit of the molecule in an ionic liquid. The electrical conductances of the dianion and neutral states differ by more than one order of magnitude. The potential-dependence of the charge-transport characteristics of the NDI molecules was confirmed by DFT calculations, which account for electrochemical double-layer effects on the conductance of the NDI junctions. This study suggests that integration of a pendant redox unit with strong coupling to a molecular backbone enables the tuning of charge transport through single-molecule devices by controlling their redox states.
Co-reporter:Cancan Huang;Dr. Songjie Chen;Kristian BaruëlØrnsø;David Reber;Masoud Baghernejad;Dr. Yongchun Fu; Thomas Wlowski; Silvio Decurtins;Dr. Wenjing Hong; Kristian Sommer Thygesen;Dr. Shi-Xia Liu
Angewandte Chemie 2015 Volume 127( Issue 48) pp:14512-14515
Publication Date(Web):
DOI:10.1002/ange.201506026
Abstract
Tuning charge transport at the single-molecule level plays a crucial role in the construction of molecular electronic devices. Introduced herein is a promising and operationally simple approach to tune two distinct charge-transport pathways through a cruciform molecule. Upon in situ cleavage of triisopropylsilyl groups, complete conversion from one junction type to another is achieved with a conductance increase by more than one order of magnitude, and it is consistent with predictions from ab initio transport calculations. Although molecules are well known to conduct through different orbitals (either HOMO or LUMO), the present study represents the first experimental realization of switching between HOMO- and LUMO-dominated transport within the same molecule.
Co-reporter:Masoud Baghernejad ; Xiaotao Zhao ; Kristian Baruël Ørnsø ; Michael Füeg ; Pavel Moreno-García ; Alexander V. Rudnev ; Veerabhadrarao Kaliginedi ; Soma Vesztergom ; Cancan Huang ; Wenjing Hong ; Peter Broekmann ; Thomas Wandlowski ; Kristian S. Thygesen ;Martin R. Bryce
Journal of the American Chemical Society 2014 Volume 136(Issue 52) pp:17922-17925
Publication Date(Web):December 15, 2014
DOI:10.1021/ja510335z
Controlling charge transport through a single molecule connected to metallic electrodes remains one of the most fundamental challenges of nanoelectronics. Here we use electrochemical gating to reversibly tune the conductance of two different organic molecules, both containing anthraquinone (AQ) centers, over >1 order of magnitude. For electrode potentials outside the redox-active region, the effect of the gate is simply to shift the molecular energy levels relative to the metal Fermi level. At the redox potential, the conductance changes abruptly as the AQ unit is oxidized/reduced with an accompanying change in the conjugation pattern between linear and cross conjugation. The most significant change in conductance is observed when the electron pathway connecting the two electrodes is via the AQ unit. This is consistent with the expected occurrence of destructive quantum interference in that case. The experimental results are supported by an excellent agreement with ab initio transport calculations.
Co-reporter:Masoud Baghernejad, David Zsolt Manrique, Chen Li, Thomas Pope, Ulmas Zhumaev, Ilya Pobelov, Pavel Moreno-García, Veerabhadrarao Kaliginedi, Cancan Huang, Wenjing Hong, Colin Lambert and Thomas Wandlowski
Chemical Communications 2014 vol. 50(Issue 100) pp:15975-15978
Publication Date(Web):04 Nov 2014
DOI:10.1039/C4CC06519K
We report an electrochemical gating approach with ∼100% efficiency to tune the conductance of single-molecule 4,4′-bipyridine junctions using scanning-tunnelling-microscopy break junction technique. Density functional theory calculation suggests that electrochemical gating aligns molecular frontier orbitals relative to the electrode Fermi-level, switching the molecule from an off resonance state to “partial” resonance.
Co-reporter:Veerabhadrarao Kaliginedi, Alexander V. Rudnev, Pavel Moreno-García, Masoud Baghernejad, Cancan Huang, Wenjing Hong and Thomas Wandlowski
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 43) pp:23529-23539
Publication Date(Web):25 Sep 2014
DOI:10.1039/C4CP03605K
The understanding of the charge transport through single molecule junctions is a prerequisite for the design and building of electronic circuits based on single molecule junctions. However, reliable and robust formation of such junctions is a challenging task to achieve. In this topical review, we present a systematic investigation of the anchoring group effect on single molecule junction conductance by employing two complementary techniques, namely scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques, based on the studies published in the literature and important results from our own work. We compared conductance studies for conventional anchoring groups described earlier with the molecular junctions formed through π-interactions with the electrode surface (Au, Pt, Ag) and we also summarized recent developments in the formation of highly conducting covalent Au–C σ-bonds using oligophenyleneethynylene (OPE) and an alkane molecular backbone. Specifically, we focus on the electron transport properties of diaryloligoyne, oligophenyleneethynylene (OPE) and/or alkane molecular junctions composed of several traditional anchoring groups, (dihydrobenzo[b]thiophene (BT), 5-benzothienyl analogue (BTh), thiol (SH), pyridyl (PY), amine (NH2), cyano (CN), methyl sulphide (SMe), nitro (NO2)) and other anchoring groups at the solid/liquid interface. The qualitative and quantitative comparison of the results obtained with different anchoring groups reveals structural and mechanistic details of the different types of single molecular junctions. The results reported in this prospective may serve as a guideline for the design and synthesis of molecular systems to be used in molecule-based electronic devices.
Co-reporter:Cancan Huang, Alexander V. Rudnev, Wenjing Hong and Thomas Wandlowski
Chemical Society Reviews 2015 - vol. 44(Issue 4) pp:NaN901-901
Publication Date(Web):2015/01/05
DOI:10.1039/C4CS00242C
Molecular electronics aims to construct functional molecular devices at the single-molecule scale. One of the major challenges is to construct a single-molecule junction and to further manipulate the charge transport through the molecular junction. Break junction techniques, including STM break junctions and mechanically controllable break junctions are considered as testbed to investigate and control the charge transport on a single-molecule scale. Moreover, additional electrochemical gating provides a unique opportunity to manipulate the energy alignment and molecular redox processes for a single-molecule junction. In this review, we start from the technical aspects of the break junction technique, then discuss the molecular structure–conductance correlation derived from break junction studies, and, finally, emphasize electrochemical gating as a promising method for the functional molecular devices.
Co-reporter:Veerabhadrarao Kaliginedi, Alexander V. Rudnev, Pavel Moreno-García, Masoud Baghernejad, Cancan Huang, Wenjing Hong and Thomas Wandlowski
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 43) pp:NaN23539-23539
Publication Date(Web):2014/09/25
DOI:10.1039/C4CP03605K
The understanding of the charge transport through single molecule junctions is a prerequisite for the design and building of electronic circuits based on single molecule junctions. However, reliable and robust formation of such junctions is a challenging task to achieve. In this topical review, we present a systematic investigation of the anchoring group effect on single molecule junction conductance by employing two complementary techniques, namely scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques, based on the studies published in the literature and important results from our own work. We compared conductance studies for conventional anchoring groups described earlier with the molecular junctions formed through π-interactions with the electrode surface (Au, Pt, Ag) and we also summarized recent developments in the formation of highly conducting covalent Au–C σ-bonds using oligophenyleneethynylene (OPE) and an alkane molecular backbone. Specifically, we focus on the electron transport properties of diaryloligoyne, oligophenyleneethynylene (OPE) and/or alkane molecular junctions composed of several traditional anchoring groups, (dihydrobenzo[b]thiophene (BT), 5-benzothienyl analogue (BTh), thiol (SH), pyridyl (PY), amine (NH2), cyano (CN), methyl sulphide (SMe), nitro (NO2)) and other anchoring groups at the solid/liquid interface. The qualitative and quantitative comparison of the results obtained with different anchoring groups reveals structural and mechanistic details of the different types of single molecular junctions. The results reported in this prospective may serve as a guideline for the design and synthesis of molecular systems to be used in molecule-based electronic devices.
Co-reporter:Masoud Baghernejad, David Zsolt Manrique, Chen Li, Thomas Pope, Ulmas Zhumaev, Ilya Pobelov, Pavel Moreno-García, Veerabhadrarao Kaliginedi, Cancan Huang, Wenjing Hong, Colin Lambert and Thomas Wandlowski
Chemical Communications 2014 - vol. 50(Issue 100) pp:NaN15978-15978
Publication Date(Web):2014/11/04
DOI:10.1039/C4CC06519K
We report an electrochemical gating approach with ∼100% efficiency to tune the conductance of single-molecule 4,4′-bipyridine junctions using scanning-tunnelling-microscopy break junction technique. Density functional theory calculation suggests that electrochemical gating aligns molecular frontier orbitals relative to the electrode Fermi-level, switching the molecule from an off resonance state to “partial” resonance.
