The supramolecular structure and van der Waals interactions affect the electronic structure of ferrocenyl-alkanethiolate SAMs on gold and silver electrodes

Cao, Liang; Li, Yuan; Yang, Ming; Nerngchamnong, Nisachol; Thompson, Damien; Yu, Xiaojiang; Qi, Dongchen; Nijhuis, Christian A.

doi:10.1039/c9na00107g

Cited by 12 publications

(18 citation statements)

References 101 publications

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“…Peak IV originates from the transition to σ* of the C–H/C–S bonds, as discussed in our earlier NEXAFS results of Au–S(CH 2 ) 11 Fc SAMs. 56 The peak assignments from the periodic DFT molecule–metal calculations are generally consistent with previous assignments from gas-phase models of S–(CH 2 ) n –Fc–(CH 2 ) 13– n molecules bound to a single Au metal atom used in our previous study. 57 …”

Section: Results and Discussionsupporting

confidence: 86%

Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces

et al. 2021

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Charge transfer (CT) dynamics across metal–molecule interfaces has important implications for performance and function of molecular electronic devices. CT times, on the order of femtoseconds, can be precisely measured using synchrotron-based core-hole clock (CHC) spectroscopy, but little is known about the impact on CT times of the metal work function and the bond dipole created by metals and the anchoring group. To address this, here we measure CT dynamics across self-assembled monolayers bound by thiolate anchoring groups to Ag, Au, and Pt. The molecules have a terminal ferrocene (Fc) group connected by varying numbers of methylene units to a diphenylacetylene (DPA) wire. CT times measured using CHC with resonant photoemission spectroscopy (RPES) show that conjugated DPA wires conduct electricity faster than aliphatic carbon wires of a similar length. Shorter methylene connectors exhibit increased conjugation between Fc and DPA, facilitating CT by providing greater orbital mixing. We find nearly 10-fold increase in the CT time on Pt compared to Ag due to a larger bond dipole generated by partial electron transfer from the metal–sulfur bond to the carbon–sulfur bond, which creates an electrostatic field that impedes CT from the molecules. By fitting the RPES signal, we distinguish electrons coming from the Fe center and from cyclopentadienyl (Cp) rings. The latter shows faster CT rates because of the delocalized Cp orbitals. Our study demonstrates the fine tuning of CT rates across junctions by careful engineering of several parts of the molecule and the molecule–metal interface.

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Section: Results and Discussionsupporting

confidence: 86%

Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces

et al. 2021

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“…Organic self-assembled monolayers (SAMs) formed on semiconductor, metal or metal oxide surfaces are an integral component of molecular electronic devices, for electrical insulation, charge storage, and charge transport. − A recent series of investigations of the charge transport properties of large-area, solid-state tunnel junctions comprised of SAMs of the redox-active ferrocenylalkanethiolates (Fc(CH 2 ) n S) , or insulating n -alkanethiolates (CH 3 (CH 2 ) n S) − have sparked renewed interest in the odd–even (or parity) effect, − which refers to the alternation of a material’s structure and/or property due to an odd or even number of repeat units in the molecule. Parity effects in solid condensed phases often arise from differences in the intermolecular interactions and molecular packing.…”

Section: Introductionmentioning

confidence: 99%

Molecular Origin of the Odd–Even Effect of Macroscopic Properties of n-Alkanethiolate Self-Assembled Monolayers: Bulk or Interface?

et al. 2020

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Elucidating the influence of the monolayer interface versus bulk on the macroscopic properties (e.g., surface hydrophobicity, charge transport, and electron transfer) of organic self-assembled monolayers (SAMs) chemically anchored to metal surfaces is a challenge. This article reports the characterization of prototypical SAMs of n-alkanethiolates on gold (CH3(CH2)nSAu, n = 6-19) at the macroscopic scale by electrochemical impedance spectroscopy and contact angle goniometry, and at the molecular level, by infrared reflection absorption spectroscopy. The SAM capacitance, dielectric constant, and surface hydrophobicity exhibit dependencies on both the length (n) and parity (nodd or neven) of the polymethylene chain. The peak positions of the CH2 stretching modes indicate a progressive increase in the chain conformational order with increasing n between n = 6 and 16. SAMs of nodd have a greater degree of structural gauche defects than SAMs of neven. The peak intensities and positions of the CH3 stretching modes are chain length independent but show an odd-even alternation of the spatial orientation of the terminal CH3. The correlations between the different data trends establish that the chain length dependencies of the dielectric constant and surface hydrophobicity originate from changes in the polymethylene chain conformation (bulk), while the odd-even variation arises primarily from a difference in the chemical composition of the interface related to the terminal group orientation. These findings provide new physical insights into the structure-property relation of SAMs for the design of ultrathin film dielectrics as well as the understanding of stereostructural effects on the electrical characteristics of tunnel junctions.

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“…Note that the electronic properties of both the functional units and the electrodes, as well as the anchor groups, should be taken into consideration when choosing the number of methylene groups to control the interface coupling, thus resulting in variation of the methylene number among different systems. [ 37–39 ] In the second aspect, we found that the relative HOMO and LUMO resonance alignment among four single‐molecule junctions displayed an odd–even effect. This finding is similar to previous reports, where the structural odd–even behaviors led to electronic odd–even effects in either ferrocene−electrode coupling [ 38 ] or molecular rectification [ 40 ] of ferrocenyl‐alkanethiolate self‐assembled monolayers.…”

Section: Resultsmentioning

confidence: 91%

“…[ 37–39 ] In the second aspect, we found that the relative HOMO and LUMO resonance alignment among four single‐molecule junctions displayed an odd–even effect. This finding is similar to previous reports, where the structural odd–even behaviors led to electronic odd–even effects in either ferrocene−electrode coupling [ 38 ] or molecular rectification [ 40 ] of ferrocenyl‐alkanethiolate self‐assembled monolayers. While odd–even conductance variation was previously observed in carbon atomic wires [ 41 ] and n‐alkanes [ 42 ] when the length of the transport junction was increased, here the odd–even effect is regarding to the FMO alignment going from AM0‐DPP to AM3‐DPP.…”

Section: Resultsmentioning

confidence: 99%

Control of Unipolar/Ambipolar Transport in Single‐Molecule Transistors through Interface Engineering

Xin

Kong

Zhang

et al. 2020

Adv Elect Materials

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To realize single‐molecule field‐effect transistors, a crucial test for evaluating the integrity of single‐molecule electronics into conventional circuit architectures, remains elusive. Though interfacial effect is widely accepted to be crucially important in electronic devices, rare reports have studied fine control of the interface in single‐molecule transistors. Through molecular engineering, different numbers of methylene groups are incorporated between the diketopyrrolopyrrole (DPP) kernel and anchor groups (AMn‐DPP, n = 0−3), and how the molecule–electrode interface affects the performance of single‐molecule transistors is investigated. Both experimental and theoretical data demonstrate that p‐type charge transport dominates in AM0‐DPP and AM1‐DPP single‐molecule transistors, while AM2‐DPP and AM3‐DPP systems exhibit ambipolar field‐effect behaviors, which is attributed to the HOMO‐pinning effect in AM0‐DPP and AM1‐DPP molecular junctions. Theoretical calculations show that the parity of the methylene number results in two different connection symmetries between the DPP kernel and graphene electrodes, and thus different electronic interactions, leading to different relative molecular energy‐level alignments form those of isolated molecules, which has never been reported before. These results provide crucial information for precise control of the interfaces in molecular junctions, new insight into building multifunctional graphene–organic hybrid electronic devices, and the design of functional organic materials.

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The supramolecular structure and van der Waals interactions affect the electronic structure of ferrocenyl-alkanethiolate SAMs on gold and silver electrodes

Abstract: Understanding the influence of structural properties on the electronic structure will pave the way for optimization of charge transport properties of SAM devices.

Cited by 12 publications

References 101 publications

Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces

Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces

Molecular Origin of the Odd–Even Effect of Macroscopic Properties of n-Alkanethiolate Self-Assembled Monolayers: Bulk or Interface?

Control of Unipolar/Ambipolar Transport in Single‐Molecule Transistors through Interface Engineering

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