In this work, we have linked the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo-/thermoswitch and the boron subphthalocyanine (BsubPc) fluorophore via an axial oligo(phenyleneethynylene) bridging unit into new DHA-BsubPc conjugates. The objectives were to elucidate the influence of BsubPc on the DHA/VHF switching reactions and the influence of DHA/VHF on the BsubPc fluorescence in these conjugates for which the entire axial substituent connected to boron comprises one large, conjugated scaffold. We present the synthesis and properties of DHA-BsubPc conjugates with varying peripheral substituents on the BsubPc core, being either unsubstituted (H(12)BsubPc) or partially fluorinated (F(6)BsubPc). Fluorination of the BsubPc core provided a remarkable increase in the reversibility of the DHA-VHF interconversions promoted by light and heat, respectively, and accompanied by on/off switching of the BsubPc fluorescence. Synthetically, the units were connected using Sonogashira coupling reactions of suitable acetylenic building blocks.

The ultimate goal of molecular electronics is to achieve practical applications. For approaching the target, we have successfully fabricated solid-state junctions based on oligo(phenylene ethynylene)s (OPEs) and cruciform OPEs with extended tetrathiafulvalene (TTF) (OPE3 and OPE3-TTF) self-assembled monolayers (SAMs) with a diamine anchoring group. SAMs were confined in micropores with gold substrates to ensure well-defined device surface areas. The transport properties were conducted on a double-junction layout, which the rGO films used for top contacts and interconnects between adjacent SAMs. The solid-state devices based on OPE3-TTF SAMs showed the expected higher conductance under ambient conditions because of the incorporation of a TTF moiety. The two devices displayed varying degrees of temperature dependence with decreasing temperature, which resulted from the cross-conjugated OPE3-TTF molecule exhibiting quantum interference while the linear-conjugated OPE3 molecule did not. This study shows the temperature dependence of the electrical properties of molecular devices based on cruciform OPEs, further enriching the research results of functional molecular devices.

Graphene‐derived materials are attractive components in conductive inks for printed and flexible electronics. Here, the authors report a facile and scalable synthesis of mildly oxidized graphite and its formulation into screen‐printable inks. The screen‐printed electrodes exhibit sheet‐resistance below 1 Ω/sq after rolling‐compression, with a compressed film thickness of ≈3 μm and line‐width resolution below 100 μm. The method, described herein, can be used without the need for substrate‐limiting post‐printing treatments, such as high‐temperature annealing, photonic annealing, or chemical reduction. The approach is applicable to any arbitrary and heat‐sensitive substrate, including plastic and paper, and is both highly cost‐effective and suitable for roll‐to‐roll printing of a wide range of devices.

A central goal in molecular electronics is to understand charge transport properties of single molecules and their ensembles. This fundamental knowledge may ultimately pave the way for electronic components constructed from tailor-made molecular building-blocks that can overcome some limits of conventional silicon-based microelectronics. The formation of robust and reproducible contact between molecule and electrode is a key challenge. At the single-molecule level, we have recently explored the use of parallel self-assembly strategies towards the formation of multiple single-molecule junctions, wherein the molecule-electrode interface is controlled with atomic precision [1]. However, the use of self-assembled monolayers (SAMs) offer a complementary approach for fabricating molecular electronic devices that are more amenable to device integration and up-scaling [2]. The presentation will highlight recent progress from our group on the fabrication and characterization of large-area molecular electronic devices employing chemically derived graphene as a soft contact-interface to the molecules. The graphene material serves a dual purpose in that it protects the underlying monolayer from filamentary damage when evaporating a metal top electrode, while itself functioning as a transparent, conducting electrode. The resulting solid-state devices are robust, permanent and can accommodate a diverse range of functional molecular layers, including e.g. photo-, redoxand bias-switches [2,3], as well as a range of molecular binding groups. Further advancement in the chemical fabrication and processing of the graphene material has recently enabled reliable measurements of our devices at cryogenic temperatures and facilitated the measurement of inelastic electron tunneling spectroscopy (IETS) [4,5].

Electron transport phenomena in molecular monolayers are complex and potentially different from those of single molecules because of, for example, molecule-molecule interactions. Unfortunately, access to detailed mechanistic investigations of molecular monolayer junctions at ultralow temperatures is typically hampered by the narrow range of operating temperatures for most large-area device platforms. Here, we present a highly optimized chemically derived graphene material with a near temperature-independent conductance profile. Using this material as a conducting interlayer electrode in solid-state molecular electronic devices, we show robust and reliable large-area molecular junction operation at temperatures ranging from room temperature to below 1 K, and we demonstrate the ability to measure inelastic electron tunneling spectroscopy of a conjugated molecular monolayer at cryogenic temperatures.

Vapor deposition of metals has long been the primary method for making contact with organic molecules in electronic devices in a fast and scalable manner. However, direct metal evaporation has proven to be the primary cause of device failure in solid-state molecular devices due to the degradation of the self-assembled molecular monolayers. The introduction of a protective interlayer between the molecular monolayer and the evaporated top electrode greatly improves the yield of working devices but at the cost of an increased internal contact resistance that depends on the nature of the interlayer and its interface with both organic molecules and metal top electrode. In the present work, we investigate the performance of a single layered graphene oxide as an atomically thin interlayer in solid-state molecular devices. We show that a single layered graphene oxide sheet is sufficient to protect an organic monolayer of alkane thiols from metal-induced degradation and short-circuiting. Remarkably, and despite graphene oxide being an insulating material, the contact resistance in our devices with a graphene oxide as a protective interlayer is similar to that of pure metal/molecule/metal junctions. We interpret this observation as graphene oxide effectively becoming part of the top electrode. The graphene oxide monolayer is thus a very promising candidate as a protective interlayer in solid-state molecular devices.

Using diamine as anchoring group, the self-assembled monolayers (SAMs) based on oligo(phenylene-ethynylene)s (OPEs) and cruciform OPEs with an extended tetrathiafulvalene (TTF) (OPE3 and OPE3-TTF) were successfully formed on the Au substrate. The uniformity and stability of SAMs were confirmed through cyclic voltammetry (CV) and electrochemical reductive desorption. The investigation of transport properties of SAMs was achieved by conducting-probe atomic force microscopy (CP-AFM) with both Au and Pt tips. The results indicated that the conductance of OPE3-TTF was 17 and 46 times that of OPE3 for Au and Pt tips, respectively. Theoretical calculations are qualitatively consistent with the experimental results, suggesting that the diamine as anchoring group has a great potential in molecular electronics.

This paper describes tunneling junctions comprising self-assembled monolayers that can be converted between resistor and diode functionality in-place. The rectification ratio is affected by the hydration of densely packed carboxylic acid groups at the interface between the top-contact and the monolayer. We studied this process by treatment with water and a water scavenger using three different top-contacts, eutectic Ga-In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO), demonstrating that the phenomena is molecular in nature and is not platform-speciffc. We propose a mechanism in which the tunneling junctions convert to diode behavior through the lowering of the LUMO, which is suffcient to bring it close to resonance at positive bias, potentially assisted by a Stark shift. This shift in energy is supported by calculations and a change in polarization observed by X-ray photoelectron spectroscopy and Kelvin probe measurements. We demonstrate light-driven modulation using spiropyran as a photoacid, suggesting that any chemical process that is coupled to the release of small molecules that can tightly bind carboxylic acid groups can be used as an external stimulus to modulate rectification. The ability to convert a tunneling junction reversibly between a diode and a resistor via an effect that is intrinsic to the molecules in the junction extends the possible applications of Molecular Electronics to reconfigurable circuits and other new functionalities that do not have direct analogs in conventional semiconductor devices.

The +6 oxidation state of iron generally exists in the form of ferrate(VI) with high redox potential and environmentally friendly nature. Although ferrate(VI) has been known for over a century, its chemistry is still limited to the solvent-based reactions that suffers from the insolubility/instability of this oxidant and the environmental issues caused by hazardous solvents. Herein, we explore the solvent-free reactivity of ferrate(VI) under mechanical milling, revealing that its strong oxidizing power is accessible in the "dry" solid state towards a broad variety of substrates, for example, aromatic alcohols/aldehydes and carbon nanotubes. More significantly, solvent-free mechanochemistry also reshapes the oxidizing ability of ferrate(VI) due to the underlying solvent-free effect and the promotive mechanical actions. This study opens up a new chemistry of ferrate(VI) with promising application in green oxidative transformation of both organic and inorganic substrates.

In processive catalysis, a catalyst binds to a substrate and remains bound while performing several consecutive reactions, as exemplified by DNA polymerases. Processivity is essential in Nature, and is often mediated by a clamp-like structure that physically tethers the catalyst to its (polymeric) template. In the case of the bacteriophage T4 replisome, a dedicated clamp protein acts as a processivity mediator by encircling DNA and subsequently recruiting its polymerase. We used this DNA-binding clamp to construct a bio-hybrid rotaxane catalyst. To this end, the clamp was conjugated to a chemical catalyst with sequence-specific oxidation behaviour. The resulting catalytic clamp could be loaded onto a DNA plasmid, and its catalytic activity was visualised using an AFM-based method that detects and spatially locates oxidised sites in DNA. It was found that both the catalytic processivity and the sliding direction of the rotaxane catalyst can be influenced by varying experimental conditions. Toroidal processive enzymes, i.e. enzymes that are able to thread onto biopolymers and to perform stepwise reactions along the polymer chain, are among the most fascinating tools involved in the clockwork machinery of life. Processive catalysis is ubiquitous in Nature and contrasts the nontemplated distributive catalysis, which is the most common mode of operation for both

The use of graphene materials as conductive inks for flexible and transparent electronics is promising, but challenged by the need for stabilizers, specialized organic solvents, and/or high temperature annealing, severely limiting performance or compatibility with substrates and printing techniques. Here, the development of a scalable water‐based graphene oxide ink is reported that can be screen‐printed on flexible plastic substrates and subsequently reduced using a 1:1 mixture of trifluoroacetic acid and hydroiodic acid, thereby creating an electric circuit. The reduced prints exhibit low sheet resistance of 327 Ω sq−1 for thin semitransparent layers with 37% transmittance. This methodology with postprinting chemical reduction outperforms high temperature annealing, thereby eliminating the need for such a step, which is incompatible with flexible plastic substrates. The strategy relies on low cost, industrially compatible chemicals and can be scaled up for low cost manufacture of roll‐to‐roll printed electronics.

Graphene oxide (GO) is an interesting material that has the potential for a wide range of applications. Critical for these applications are the type of oxygen bond and its spatial distribution on the individual GO sheets. This distribution is not yet well understood. Few techniques offer a resolution high enough to unambiguously identify oxygen configuration. We used a new, label free spectroscopic technique to map oxygen bonding on GO, with spatial resolution of nanometres and high chemical specificity. AFM-IR, atomic force microscopy coupled with infrared spectroscopy, overcomes conventional IR diffraction limits, producing IR spectra from specific points as well as chemical maps that are coupled to topography. We have directly observed oxygen bonding preferentially on areas where graphene is folded, in discrete domains and on edges of GO. From these observations, we propose an updated structural model for GO, with CO on its edge and plane, which confirms parts of earlier proposed models. The results have interesting implications. Determining atomic position and configuration from precise imaging offers the possibility to link nanoscale structure and composition with material function, paving the way for targeted tethering of ions, polymers and biomaterials.

The structure of graphene oxide (GO) is a matter of discussion. While established GO models are based on functional groups attached to the carbon framework, another frequently used model claims that GO consists of two components, a slightly oxidized graphene core and highly oxidized molecular species, oxidative debris (OD), adsorbed on it. Those adsorbents are claimed to be the origin for optical properties of GO. Here, we examine this model by preparing GO with a low degree of functionalization, combining it with OD and studying the optical properties of both components and their combination in an artificial two-component system. The analyses of absorption and emission spectra as well as lifetime measurements reveal that properties of the combined system are distinctly different from those of GO. That confirms structural models of GO as a separate oxygenated hexagonal carbon framework with optical properties governed by its internal structure rather than the presence of OD. Understanding the structure of GO allows further reliable interpretation of its optical and electronic properties and enables controlled processing of GO.

The formation, characterization, and purification of well-defined stoichiometric clusters of metallic nanoparticles, particularly in the form of dimers or trimers, are important and formidable challenges in nanoscience. Here we show that flow cytometry can be used as a high-throughput method to determine the relative distribution of oligomeric clusters of molecularly linked gold nanoparticles in bulk solution at the single-particle level with good statistics. This unique information would be near impossible to obtain using traditional characterization techniques. The flow cytometric approach is utilized to provide fast feedback for the synthesis optimization of the complex reaction between citrate-stabilized gold nanoparticles and bi-functional molecular wires with dithiocarbamate anchoring groups. Finally, we demonstrate that flow cytometry can be used to significantly increase the proportion of AuNP dimers from an oligomer-rich polydisperse sample by size-selective sorting.

2D materials heterostructures are built by vertical stacking of solution‐processed reduced graphene oxide (rGO) film and few‐layer MoS2. The Raman and photoluminescence of the MoS2/rGO heterostructures show more significant peak shift compared to individual MoS2 or rGO film. The field‐effect transistors (FETs) based on such MoS2/rGO heterostructures show ambipolar behavior in the dark but n‐type behavior under illumination. This phenomenon provides a way to investigate the charge transport in valence band of MoS2. Due to charge separation caused by built‐in potential at MoS2/rGO interface, the recombination of photoexcited electron–hole pairs is effectively suppressed, leading to high photoresponsivity (≈2.4 × 104 A W−1) and photogain (≈4.7 × 104) of the MoS2/rGO heterostructures in ambient air with modulation of gate bias and drain–source bias.

Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO–LUMO energy gaps. OPE3, OPE3–DTF, and OPE3–tetrathiafulvalene (TTF) can form good self‐assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe–atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3–TTF > OPE3–DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero‐bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.

Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable 'planar' manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.