A new azobenzene-thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7 x 10(3) (with an average value of 1.5 x 10(3)) is reported. The "on" conductance state is clearly identified to the cis isomer of the azobenzene moiety. The high on/off ratio is explained in terms of photoinduced, configuration-related changes in the electrode-molecule interface energetics (changes in the energy position of the molecular orbitals with respect to the Fermi energy of electrodes) in addition to changes in the tunnel barrier length (length of the molecules). First principles density functional calculations demonstrate a better delocalization of the frontier orbitals as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one. Measured photoionization cross sections for the molecules in the SAM are close to the known values for azobenzene derivatives in solution.

Immobilization of an azobenzene-bithiophene compound on a gold surface leads to self-assembled monolayers with photoswitchable electrical properties.

We report on hybrid memristive devices made of a network of gold nanoparticles (10 nm diameter) functionalized by tailored 3,4-(ethylenedioxy)thiophene (TEDOT) molecules, deposited between two planar electrodes with nanometer and micrometer gaps (100 nm to 10 μm apart), and electro-polymerized in situ to form a monolayer film of conjugated polymer with embedded gold nanoparticles (AuNPs). Electrical properties of these films exhibit two interesting naphthalenethiol 8 or with 1-dodecanethiol 9 , a perylene derivative with Au nanoparticles 10 , pentacene films with embedded Au nanoparticles 11;12 . Some of these previous reports claimed, in addition to resistive switching, the observation of a Negative Differential Resistance (NDR) in the device. 3;5;6 However in these previous works, devices have a vertical sandwich structure consisting in a metal/switching layer/metal stack where the hybrid material is localized between top and bottom electrodes. In these devices two approaches were used to form the hybrid material: (i) by mixing the organic material with the nanoparticles in solution and depositing the blend by spincoating on the surface; or (ii) by evaporation of an ultra-thin metallic layer (usually 5 nm) onto the organic layer in order to form metal clusters or nanoparticles 13 . Furthermore, resistive memories and their extension to memristive systems have opened new routes toward innovative computing solutions such as logic-in-memory (implication logic with memristor) 14 , analog computing (threshold logic with memristor 15 ) or neuromorphic computing 16 .Nevertheless, to become attractive, these different approaches require a massive integration of memory elements. If crossbar integration consisting in vertical devices interconnected between metallic lines and columns has been considered as an interesting solutions, its practical realization with standard lithographic technics (i.e. top-down approaches) is facing severe limitations such as wire resistance contribution, crosstalk of memory elements during programming and sneak path during reading. One relatively unexplored solution is to rely on bottom-up approaches based on randomly assembly elements, in which memory functionalities are configured post-fabrication.This idea was initially proposed with the concept of nanocell 17;18;19 but remains in its early steps of development from a practical viewpoint and would benefit from functional and reliable hardware for its implementation.Here, we report on a hybrid organic/gold nanoparticle memory with several advances compared to the devices demonstrated until now: (i) a nanoscale -monolayer thick-planar structure: the hybrid organic/gold nanoparticle material is placed between two coplanar electrodes with characteristic distance smaller than 100 nm; (ii) a bottom-up approach for material synthesis, device fabrication and operation: redox ligands were electro-polymerized in situ (i.e. into the device) to form a monolayer of a conjugated polymer with embedded Au nanoparticles and the memory functionality is def...

Four methanofullerene derivatives, with phosphonate or sulfone groups attached to a C(60) core through a Bingel procedure, were synthesized to probe their stability upon electrolytic reduction. Derivatives 1 and 2 are the most stable upon electroreduction and do not exhibit retro-cyclopropanation reactions until more than three electrons per C(60) derivative are transferred. The cyclopropane ring is then removed and C(60)(>CH(2))(n) (n=1-3) products result from reactions of the trianion of C(60) with the solvent, CH(2)Cl(2). The situation with diphosphonate 3 or phosphonatecarboxylate 4 is dramatically different. For 3, quantitative retro-cyclopropanation occurs when 2.8 e(-) per molecule are transferred. In the case of 4, when more than two electrons per molecule are transferred, there is evidence of the reversible formation of a very stable intermediate, which is oxidized at a potential 500 mV more positive than the first fullerene-based reduction of the parent compound. Electrolysis of a simple C(70)-Bingel monoadduct (5) also exhibits the formation of a similar intermediate. On the basis of cyclic voltammetry, ESR spectroscopy, and MALDI analysis of products, the intermediate observed during the electrolysis of compounds 4 and 5 is assigned to a dimeric structure.

The synthesis of a series of bithiophenic precursors of electrogenerated conjugated polymers functionalized by bipyridine ligands is described. The precursor structure involves two polymerizable groups attached at both ends of a bipyridine ligand and fixed at an internal b-position of thiophene via an alkylsulfanyl or alkoxy spacer. Electrochemical and optical data show that the low polymerization potential resulting from the association of 3,4-ethylenedioxythiophene (EDOT) and alkylsulfanyl or alkoxy thiophene combined with the multi-site polymerization approach allows a straightforward electrosynthesis of extensively conjugated and stable functionalized polymers. On the basis of these results, iron and ruthenium complexes of these precursors have been synthesized and electropolymerized. The analysis of the electrochemical behavior of the resulting polymers shows that they exhibit the typical electrochemical signature of both the conjugated polythiophene backbone and the immobilized metal complex.{ Electronic supplementary information (ESI) available: synthetic procedures and analytical detail for all compounds. See

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Self‐assembled monolayers (SAMs) of a conjugated bithiophenic system connected to an alkanethiol chain have been deposited on gold surface. The electroactive bithiophenic system involves a 3,4‐ethylenedioxythiophene (EDOT) unit and a thiophene ring on which an alkanethiol is attached at the internal β‐position via a sulfide linkage. The analysis of the structure of the SAMs by IR spectroscopy, ellipsometry, contact angle measurement and X‐ray photoelectron spectroscopy (XPS) provides consistent results indicating compact monolayers in which the alkyl linkers are arranged in an almost vertical fashion while the bithiophenic‐conjugated systems are essentially parallel to the surface. Cyclic voltammetry shows that application of a few potential scans to SAMs immersed in a medium containing only a supporting electrolyte leads to the typical electropolymerization curves while the CV of the electrooxized monolayer exhibits a reversible cyclic voltammogram characteristic of a stable electroactive extended conjugated system. The characterization of the electropolymerized monolayers by IR spectroscopy, ellipsometry, contact angle measurement, and XPS indicates compact monolayers. The analysis of the current voltage characteristics of the monolayers by conducting AFM before and after electrooxidation shows that the enhancement of the effective conjugation resulting from electropolymerization leads to a significant increase of the transport properties.

Molecular junctions and switches are a focus of considerable current interest as possible basic components of future molecular electronic devices. [1,2] During the past decades molecular switches based on different concepts and mechanisms have been proposed, synthesized and investigated. [3] These include reversible bond breaking, [1,4,5] translocation of part of multi-components molecular assemblies, [6,7] proton transfer, [1,4,8] or reversible conformational changes of a system with geometry-dependent electronic properties. [9][10][11] The interplay of the cation-binding properties of crown-ether and conformational changes has already been investigated. Thus, Shinkai used the photoisomerization of azobenzene units inserted in crown ether systems to modulate the cation binding properties of the cavity. [12] From a different viewpoint, we have shown that the cation-binding ability of a polyether loop Accepted to 2 attached at two fixed points of an oligothiophene chain can serve as driving force to generate changes in the geometry and hence electronic properties of the conjugated system. [13] A similar approach has been previously used for the synthesis of polythiophene-based sensors [14] and more recently for the control of the intramolecular photoinduced electron transfer in crown ether bridged oligothiophenes. [15] In this context, we now report on the surface immobilization by double fixation on gold surface of a dithiol quaterthiophene 1-SH derivatized with a polyether loop (Scheme 1). In recent years we have extensively studied the structural conditions and synthetic approaches allowing the horizontal double fixation of conjugated oligothiohenes as monolayers on gold surface. [16] After an analysis of the cation complexation properties of the related acetylprotected dithiol molecule 1 in solution by UV-Vis spectroscopy and cyclic voltammetry, the preparation of monolayers by double fixation of the oligothiophene chain on gold surface will be described, the structure properties of these monolayers will be investigated using cyclic voltammetry, ellipsometry, water contact angle measurement, XPS and their electrical properties will be assessed by contacting the monolayer with a conducting eutectic GaIn drop.Finally preliminary results on the cation binding properties of the monolayer and investigations on the use of the immobilized molecule as a switchable molecular junction will be presented and possible transport mechanisms will be discussed. Scheme 1Compound 1 has been synthesized by deprotection/functionalization of the appropriately protected thiolate groups according to the already published method. [16b] The detailed synthesis of this molecule and of some parent compounds will be reported elsewhere. [17] The identity and purity of compound 1 were established by 1 H and 13 C NMR spectrometry and HR mass spectrometry giving satisfactory results (see Supporting Information). Dithiol 1-SH was prepared by reduction of the thioester groups of 1 using DIBAl-H. Monolayers were Accepted to 3 elabo...