The study of Langmuir monolayers incorporating biomimetic and bioactive substances plays an important role today in assessing the properties and quality of the molecular films for potential ...biomedical applications. Here, miscibility of binary and ternary monolayers of phospholipid (dioleoyl phosphatidylcholine, DOPC), immunosuppressant (cyclosporine A, CsA), and antioxidant (lauryl gallate, LG) of varying molar fractions was analyzed by means of the Langmuir technique coupled with a surface potential (ΔV) module at the air–water interface. The surface pressure–area per molecule (π–A) isotherms provided information on the physical state of the films at a given surface pressure, the monolayer packing and ordering, and the type and strength of intermolecular interactions. Surface potential–area (ΔV–A) isotherms revealed the molecular orientation changes at the interface upon compression. In addition, the apparent dipole moment of the monolayer-forming molecules was determined from the surface potential isotherms. The obtained results indicated that the film compression provoked subsequent changes of CsA conformation and/or orientation, conferring better affinity for the hydrocarbon environment. The mutual interactions between the components were analyzed here in terms of the excess and total Gibbs energy of mixing, whose values depended on the stoichiometry of the mixed films. The strongest attraction, thus the highest thermodynamic stability, was found for a DOPC–CsA–LG mixture with a 1:1:2 molar ratio. Based on these results, a molecular model for the organization of the molecules within the Langmuir film was proposed. Through this model, we elucidated the significant role of LG in improving the miscibility of CsA in the model DOPC membrane and thus in increasing the stability of self-assembled monolayers by noncovalent interactions, such as H-bonds and Lifshitz–van der Waals forces. The above 1:1:2 combination of three components is revealed as the most promising film composition for the modification of implant device surfaces to improve their biocompatibility. Further insight into mechanisms concerning drug–membrane interactions at the molecular level is provided, which results in great importance for biocoating design and development as well as for drug release at target sites.
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IJS, KILJ, NUK, PNG, UL, UM
The societal impact of the electronics industry is enormous—not to mention how this industry impinges on the global economy. The foreseen limits of the current technology—technical, economic, and ...sustainability issues—open the door to the search for successor technologies. In this context, molecular electronics has emerged as a promising candidate that, at least in the short-term, will not likely replace our silicon-based electronics, but improve its performance through a nascent hybrid technology. Such technology will take advantage of both the small dimensions of the molecules and new functionalities resulting from the quantum effects that govern the properties at the molecular scale. An optimization of interface engineering and integration of molecules to form densely integrated individually addressable arrays of molecules are two crucial aspects in the molecular electronics field. These challenges should be met to establish the bridge between organic functional materials and hard electronics required for the incorporation of such hybrid technology in the market. In this review, the most advanced methods for fabricating large-area molecular electronic devices are presented, highlighting their advantages and limitations. Special emphasis is focused on bottom-up methodologies for the fabrication of well-ordered and tightly-packed monolayers onto the bottom electrode, followed by a description of the top-contact deposition methods so far used.
In this work, the influence of the rigid substrate on the determination of the sample Young's modulus, the so‐called bottom‐effect artifact, is demonstrated by an atomic force microscopy ...force‐spectroscopy experiment. The nanomechanical properties of a one‐component supported lipid membrane (SLM) exhibiting areas of two different thicknesses are studied: While a standard contact mechanics model (Sneddon) provides two different elastic moduli for these two morphologies, it is shown that Garcia's bottom‐effect artifact correction yields a unique value, as expected for an intrinsic material property. Remarkably, it is demonstrated that the ratio between the contact radius (and not only the indentation) and the sample thickness is the key parameter addressing the relevance of the bottom‐effect artifact. The experimental results are validated by finite element method simulations providing a solid support to Garcia's theory. The amphiphilic nature of the investigated material is representative of several kinds of lipids, suggesting that the results have far reaching implications for determining the correct Young's modulus of SLMs. The generality of Garcia's bottom‐effect artifact correction allows its application to every kind of supported soft film.
An atomic force microscopy force‐spectroscopy experiment is designed to investigate the so‐called bottom‐effect artifact affecting the nanomechanical properties of a supported lipid bilayer. While standard contact mechanics does not compensate this artifact, a full support is provided to Garcia's theory as the proper approach to measure the correct Young's modulus of soft samples supported on rigid substrates.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Nascent molecular electronic devices based on linear 'all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of ...trimethylsilyl end groups from an oligoyne, Me
Si-(Ctriple bond, length as m-dashC)
-SiMe
(1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|Ctriple bond, length as m-dashCCtriple bond, length as m-dashCCtriple bond, length as m-dashCCtriple bond, length as m-dashCSiMe
(Au|C
SiMe
). In the second stage, treatment of Au|C
SiMe
with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|Ctriple bond, length as m-dashCCtriple bond, length as m-dashCCtriple bond, length as m-dashCCtriple bond, length as m-dashCH (Au|C
H). The reactive terminal Ctriple bond, length as m-dashC-H moiety in Au|C
H can be modified by 'click' reactions with (azidomethyl)ferrocene (N
CH
Fc) to introduce a redox probe, to give Au|C
C
N
HCH
Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C
H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures Au|C
|GNP in which the monolayer of linear, 'all-carbon' C
chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C
C
N
HCH
Fc systems and after formation of the gold top-contact electrode in Au|C
|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices Au|C
|GNP featuring 'all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.
Attaining precise control over molecular arrangements is of paramount importance for numerous applications in nanotechnology, particularly in constructing molecular templates to accurately immobilize ...target materials on surfaces. A strategic combination of supramolecular and interfacial chemistry may serve to build a well‐organized molecular network, enabling the subsequent location of target molecules on specific positions of a surface. A supramolecular complex (compound 1) comprised of a melamine unit forming hydrogen bonds with dendritic arms terminated in a coumarin unit is utilized, which readily undergoes photodimerization. The research demonstrates the formation of well‐organized Langmuir films of compound 1 which can be transferred on substrates at low surface pressures adopting a lying‐flat orientation. Upon irradiation of the pristine films at 365 nm the coumarin units undergo photo‐cross linking, leading to the formation of a compact photo‐crosslinked film. Incubation of these photo‐crosslinked films in a solution containing 1‐hexanethiol results in the withdrawal of the melamine and the chemisorption of two thiol molecules per each melamine unit. The nanopores created by the removal of the melamine core are attributed to the disruption of hydrogen bonds in compound 1 by the thiols. This precisely defined molecular network holds significant promise as a template for orchestrating the arrangement of functional materials on surfaces.
Molecular Templates: strategic combination of supramolecular chemistry and nanoarchitectonic tools to precisely guide the specific location of target molecules on surfaces.
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The compounds and complexes 1,4‐C6H4(C≡C‐cyclo‐3‐C4H3S)2 (2), trans‐Pt(C≡C‐cyclo‐3‐C4H3S)2(PEt3)2 (3), trans‐Ru(C≡C‐cyclo‐3‐C4H3S)2(dppe)2 (4; dppe=1,2‐bis(diphenylphosphino)ethane) and ...trans‐Ru(C≡C‐cyclo‐3‐C4H3S)2{P(OEt)3}4 (5) featuring the 3‐thienyl moiety as a surface contacting group for gold electrodes have been prepared, crystallographically characterised in the case of 3–5 and studied in metal|molecule|metal junctions by using both scanning tunnelling microscope break‐junction (STM‐BJ) and STM‐I(s) methods (measuring the tunnelling current (I) as a function of distance (s)). The compounds exhibit similar conductance profiles, with a low conductance feature being more readily identified by STM‐I(s) methods, and a higher feature by the STM‐BJ method. The lower conductance feature was further characterised by analysis using an unsupervised, automated multi‐parameter vector classification (MPVC) of the conductance traces. The combination of similarly structured HOMOs and non‐resonant tunnelling mechanism accounts for the remarkably similar conductance values across the chemically distinct members of the family 2–5.
Conducting alone: The single‐molecule conductance of 3‐thienyl contacted organic and organometallic complexes displays remarkable invariance, as determined by both scanning tunnelling microscope break‐junction (STM‐BJ) analysis and I(s) measurements.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Conductance across a metal|molecule|metal junction is strongly influenced by the molecule-substrate contacts, and for a given molecular structure, multiple conductance values are frequently observed ...and ascribed to distinct binding modes of the contact at each of the molecular termini. Conjugated molecules containing a trimethylsilylethynyl terminus, -C≡CSiMe(3) give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites.
Nascent molecular electronic devices, based on monolayer Langmuir–Blodgett films sandwiched between two carbonaceous electrodes, have been prepared. Tightly packed monolayers of ...4‐((4‐((4‐ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid are deposited onto a highly oriented pyrolytic graphite electrode. An amorphous carbon top contact electrode is formed on top of the monolayer from a naphthalene precursor using the focused electron beam induced deposition technique. This allows the deposition of a carbon top‐contact electrode with well‐defined shape, thickness, and precise positioning on the film with nm resolution. These results represent a substantial step toward the realization of integrated molecular electronic devices based on monolayers and carbon electrodes.
All‐carbon electrode molecular electronic devices comprising a Langmuir–Blodgett monolayer of an organic “molecular wire” sandwiched between two carbonaceous electrodes are fabricated. The bottom electrode is highly oriented pyrolytic graphite and the top contact electrode is deposited with nm precision over the position and shape by focused electron beam induced deposition to give “all‐carbon” electrode molecular electronic devices.
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The design and synthesis of Aviram–Ratner‐type molecular rectifiers, featuring an anilino‐substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ‐spacer ...bicyclo2.2.2octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X‐ray analysis. The photophysical properties of the TTF‐BCO‐exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir–Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current–voltage (I–V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I–V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.
Aviram–Ratner mechanism of rectification: A molecular dyad, closely resembling the original design by Aviram and Ratner, featuring a strong donor (TTF), separated by a rigid insulating σ‐spacer from a strong extended TCNQ acceptor (exTCNQ), has been designed, synthesized, and fully characterized. Langmuir–Blodgett films were prepared and showed the asymmetric current–voltage (I–V) curve characteristic for rectification, whereas control compounds containing the TTF but not the exTCNQ unit or featuring the exTCNQ acceptor moiety but lacking the TTF donor showed symmetric I–V curves.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Future applications of single‐molecular and large‐surface area molecular devices require a thorough understanding and control of molecular junctions, interfacial phenomena, and intermolecular ...interactions. In this contribution the concept of single‐molecule junction and host‐guest complexation to sheath a benchmark molecular wire–namely 4,4′‐(1,4‐phenylenebis(ethyne‐2,1‐diyl))dianiline – with an insulating cage, pillar5arene 1,4‐diethoxy‐2‐ethyl‐5‐methylbenzene is presented. The insertion of one guest molecular wire into one host pillar5arene is probed by 1H‐NMR (nuclear magnetic resonance), whilst the self‐assembly capabilities of the amine‐terminated molecular wire remain intact after complexation as demonstrated by XPS (X‐ray photoelectron spectroscopy) and AFM (atomic force microscopy). Encapsulation of the molecular wire prevents the formation of π‐ π stacked dimers and permits the determination of the true single molecule conductance with increased accuracy and confidence, as demonstrated here by using the STM–BJ technique (scanning tunneling microscopy– break junction). This strategy opens new avenues in the control of single‐molecule properties and demonstrates the pillararenes capabilities for the future construction of arrays of encapsulated single‐molecule functional units in large‐surface area devices.
Encapsulation of molecular wires: determination of ‘true’ single molecule conductance // formation of large area molecular devices composed of extended arrays of single‐molecules.
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