270 research outputs found
Correlations of Electrical Properties and Molecular Structure Measured by Junctions Incorporating Self Assembled Monolayers
No full textElectron transfer processes through organic molecules have been studied extensively i) in the last 30 years using transient spectroscopy in donor-acceptor supramolecular systems1 ii) in the last decade using an electrochemical approach in self assembled monolayers (SAMs) organized at the electrode interface. 2 We measured electron transfer rate through molecular systems as current flowing between molecules sandwiched between two metal electrodes.
Fabrication of metal-molecule-metal junction is a challenging task. We report a series of studies of electron transfer processes carried out in junctions that are based on Hg electrodes (Fig 1), Hg-SAM//SAM-M, where M is a metal surface (Au, Ag, Hg). The junctions are easy to assemble (because the mercury electrode is compliant) and compatible with SAMs incorporating organic groups having a range of structures. We used two different types of junction. 1)Two electrodes junctions are used to measure the current flowing through SAMs of different chemical structure, sandwiched between the electrodes and to correlate electron transfer rate with the chemical structure of molecules (Interfacers 1 and 2 in Fig 1).3,4,5 . When photoactive molecules are incorporate in the SAMs, the current flowing through the junction changes upon irradiation
MaECENAS: Nano-scale Optical-to-Mechanical Energy Conversion: Coupling Nano-Objects with Light-Powered Molecular Lifters
No full textWe aim to demonstrate that is possible to move vertically and horizontally nano-objects by coupling them to photoactive self assembled monolayers (SAMs) of molecular rods incorporating azo units, and to use the reversible azo SAMs light induced molecular movements to express controlled mechanical work. We have recently reported that a large area azo SAM can act as a reversible light-powered cargo lifter (Figure 1). Now, by using a vriety of techniques, we intend to determine the maximum force expressed by the azo SAMs under irradiation, by increasing the weight of the coupled nano-object. The experimental data will be interpreted by theoretical models, to estimate the effect of the environment on the strength of the molecular cargo lifter. A periodic and laterally moving interference pattern can be generated optically triggering the cis-trans isomerization of the azo SAM (Figure 2). In such an environment a nanoscale object should in principle display a lateral movement on the SAM surface
Self Assembled Monolayers organized between two Metal Surfaces. Correlation between Electrical Properties and Molecular Structure.
No full textElectron transfer processes through organic molecules have been studied extensively i) in the last 30 years using transient spectroscopy in donor-acceptor supramolecular systems1 ii) in the last decade using an electrochemical approach in self assembled monolayers (SAMs) organized at an electrode interface. 2
We report a series of studies of electron transfer processes carried out by measuring current flowing though molecules in metal-molecules-metal junctions. We used two different types of junction: a two electrodes junction and in a four electrodes junction. In the first case, we correlate electron transfer rate with the chemical structure of molecules, by measuring the current flowing through SAMs sandwiched between two electrodes (Fig 1a,b).3,4,5,6 The junctions are based on Hg electrodes: Hg-SAM//SAM-M, where M is a metal surface (Au, Ag, Hg), are easy to assemble and are compatible with SAMs incorporating organic molecules having a range of structures. When photoactive molecules are incorporated into the SAMs, the current flowing through the junction changes upon irradiation of the SAMs.
In the second type of junction (Fig 1c,d), that incorporates redox sites, the potentials of the electrodes respect to the potential of the redox center are controlled: The current flowing between the electrodes shows the behaviour of a solid state transistor
Test-beds for Molecular Electronics: Metal–Molecules–Metal Junctions Based on Hg Electrodes
No full text
Junctions based on mesoscopic Hg electrodes are used to characterize the electrical properties of the organic molecules organized in self-assembled monolayers (SAMs). The junctions M-SAM//SAM-Hg are formed by one electrode based on metals (M) such as Hg, Ag, Au, covered by a SAM, and
by a second electrode always formed by a Hg drop carrying also a SAM. The electrodes, brought together by using a micromanipulator, sandwich SAMs of different nature at the contact area (?0.7 ?m2). The high versatility of the system allows a series of both electrical and electrochemical
junctions to be assembled and characterized: i) The compliant nature of the Hg electrodes allows incorporation into the junction and measurement of the electrical behavior of a large number of molecular systems and correlation of their electronic structure to the electrical behavior; ii) by
functionalizing both electrodes with SAMs exposing different functional groups, X and Y, it is possible to compare the rate of electron transfer through different X···Y molecular interactions; iii) when the junction incorporates one of the electrode formed by a semitransparent
film of Au, it allows electrical measurements under irradiation of the sandwiched SAMs. In this case the junction behaves as a photoswitch; iv) incorporation of redox centres with low lying, easily reachable energy levels, provides electron stations as indicated by the hopping mechanism dominating
the current flow; v) electrochemical junctions incorporating redox centres by both covalent and electrostatic interactions permit control of the potential of the electrodes with respect to that of the redox state by means of an external reference electrode. Both these junctions show an electrical
behavior similar to that of conventional diodes, even though the mechanism generating the current flow is different. These systems, demonstrating high mechanical stability and reproducibility, easy assembly, and a wide variety of produced results, are convenient test-beds for molecular electronics
and represent a useful complement to physics-based experimental methods.
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Electron Transfer in a Hg‐SAM//SAM‐Hg Junction Mediated by Redox Centers
No full textCurrent affairs: The electron-transport properties of a metal-molecule-metal junction based on two contacting redoxactive self-assembled monolayers of [Ru(NH3)5(NC5H 4-4-CH2NHCO(CH2)10-SH](PF 6)2 (see picture) is described. The junction becomes conductive when the electrode potentials are adjusted to the formal potential of the redox centers and shows diode- and transistor-like characteristics analogous to those of solid-state devices
Covalently Linked Systems Containing Metal Complexes
No full textThe aim of this Chapter is to provide an overview of photoinduced electron transfer (PET) in covalently linked systems containing metal complexes. In bimetallic dyads, energy transfer (EnT) and PET are often strongly intertwined, either as competitive or as mechanistically related processes. Therefore, the discussion will include, when required, EnT results as well
Electron exchange between two electrodes mediated by two electroactive adsorbates
No full textElectrochemical junctions are used to incorporate and study teh electtron transport mediated by redox centres. Theoretical model interpret the data of the molecular transistor behavior
Gating current flowing through molecules in metal-molecules-metal junctions
No full textWe have assembled two junctions that incorporate redox sites between Hg electrodes by different interactions. In the first junction, Hg-SAM-R//R-SAM-Hg, the redox site (R) are covalently linked to each electrode in self assembled monolayers (SAM-R). In the second junction, Hg-SAM//R//SAM-Hg, the redox sites dissolved in solution are trapped by electrostatic interaction at the SAM formed at the electrodes. The current flowing through these junctions can be controlled by adjusting the potential applied at the electrodes respect to the redox potential of the species by using an electrochemical system. The current flowing in these two junctions is mediated by the redox sites through different mechanisms. In particular, the current flowing through junction Hg-SAM-R//R-SAM-Hg occurs through a self exchange mechanism between the redox sites organized at each electrode, while the current flowing through junction Hg-SAM//R//SAM-Hg is dominated by a redox- cycling mechanism. The systems described here are easy to assemble, well-characterized, yield reproducible data and make it easy to modify the electrical properties of the junctions by changing the nature of the redox centres. For these characteristics they are well suited for collecting fundamental information relevant to the fabrication of molecular switches
Controlling the Electron Transfer Mechanism in Metal-Molecules-Metal Junctions
No full textWe show how the mechanism of electron transfer through molecules can be switched between different regimes by using a simple Hg-based metal-molecules-metal junction that allows for hosting of self-assembled monolayers (SAMs) of a large variety of molecular systems. We compare here the results obtained by using two different approaches in measuring electron transfer rate. Using a two-electrode assembly we have measured I-V curves through SAMs formed by different organic molecules (alkanethiols HS(CH2)n-1CH3 (n = 8, 10, 12, 14, 16), oligophenylene thiols HS(C6H4)kH (k = 1, 2, 3), or benzylic homologs of the oligophenylene thiols HSCH2(C6H4)mH (m = 1, 2, 3). The molecules incorporated have a very large HOMO-LUMO energy separation and their orbitals cannot align with the Fermi levels of the electrodes under an applied voltage. The molecules therefore behave as insulators, and the electron transport mechanism is characterized by a through-bond tunneling process. Using an electrochemical junction we have measured I-V curves through SAMs of molecules incorporating redox sites (ruthenium pentaamine pyridine-terminated thiol [HS(CH2)10CONHCH2pyRu(NH3)5](PF6)2). The incorporated redox sites have energetically low molecular orbitals which can align with the Fermi levels of the electrodes. A four-electrode configuration of the electrochemical junction allows control of the potentials of the electrodes with respect to the redox potential of the incorporated redox-active molecules. We show that under this control of potential the electron transport mechanism can be switched to different regimes and the current flowing through the junction can be modulated
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