Metal–organic frameworks (MOFs) containing redox active linkers have led to hybrid compounds exhibiting high electrical conductivity, which enables their use in applications in electronics and ...electrocatalysis. While many computational studies predict two-dimensional (2D) MOFs to be metallic, the majority of experiments show decreasing conductivity on cooling, indicative of a gap in the electronic band structure. To date, only a handful of MOFs have been reported that exhibit increased electrical conductivity upon cooling indicative of a metallic character, which highlights the need for a better understanding of the origin of the conductivity. A 2D MOF containing iron bis(dithiolene) motifs was recently reported to exhibit semiconducting behavior with record carrier mobility. Herein, we report that high crystallinity and the elimination of guest species results in an iron 2,3,6,7,10,11-tripheylenehexathiolate (THT) MOF, FeTHT, exhibiting a complex transition from semiconducting to metallic upon cooling, similar to what was shown for the analogous CoTHT. Remarkably, exposing the FeTHT to air significantly influences the semiconducting-to-metallic transition temperature (100 to 300 K) and ultimately results in a material showing metallic-like character at, and above, room temperature. This study indicates these materials can tolerate a substantial degree of doping that ultimately results in charge delocalization and metallic-like conductivity, an important step toward enabling their use in chemiresistive sensing and optoelectronics.
Single-molecule one-dimensional topological insulator (1D TI) is a class of molecular wires that exhibit increasing conductance with wire length. This unique trend is due to the coupling between the ...two low-lying topological edge states of 1D TIs described by the Su–Schrieffer–Heeger model. In principle, this quantum phenomenon within 1D TIs can be utilized to achieve long-range gating in molecular conductors. Here, we study electron transport through a single-edge state of doubly oxidized oligophenylene bis(triarylamine) to understand the effect of the edge state coupling on conductance. We find that conductance is elevated by approximately 1 order of magnitude compared to a control molecule with the same conductance pathway. Density function theory calculations further support that the increase in conductance is due to the interaction between the edge states of 1D TIs. This work demonstrates a new gating paradigm in molecular electronics, while also providing a deeper understanding of how edge states interact and affect electron transport within 1D TIs.
As social media platforms continue to grow in popularity, there is an increasing need for science outreach teams to bring STEM content to the virtual landscape. Here, we highlight the use of ...short-form videos on our TikTok channel@IvyLeagueScienceas a new way to approach science outreach. Through a combination of content production and data analytics, we were able to build an online platform with >150k followers, 3.6 million likes, and 18 million views. By bringing science to social media, we engage with students across the world, allowing them to experience science-based content. In this case study, we hope to encourage other scientific outreach teams to employ social media as a means of increasing visibility of scientists and STEM careers.
Coherent tunneling electron transport through molecular wires has been theoretically established as a temperature-independent process. Although several experimental studies have shown counter ...examples, robust models to describe this temperature dependence have not been thoroughly developed. Here, we demonstrate that dynamic molecular structures lead to temperature-dependent conductance within coherent tunneling regime. Using a custom-built variable-temperature scanning tunneling microscopy break-junction instrument, we find that oligonphenylenes exhibit clear temperature-dependent conductance. Our calculations reveal that thermally activated dihedral rotations allow these molecular wires to have a higher probability of being in a planar conformation. As the tunneling occurs primarily through π-orbitals, enhanced coplanarization substantially increases the time-averaged tunneling probability. These calculations are consistent with the observation that more rotational pivot points in longer molecular wires leads to larger temperature-dependence on conductance. These findings reveal that molecular conductance within coherent and off-resonant electron transport regimes can be controlled by manipulating dynamic molecular structure.
Here, we describe the synthesis of the hexameric macrocyclic aniline (MA6), which spontaneously assembles into coaxially conductive organic wires in its oxidized and acidified emeraldine salt (ES) ...form. Electrical measurements reveal that ES-MA6 exhibits high electrical conductivity (7.5 × 10–2 S·cm–1) and that this conductivity is acid–base responsive. Single-crystal X-ray crystallography reveals that ES-MA6 assembles into well-defined trimeric units that then stack into nanotubes with regular channels, providing a potential route to synthetic nanotubes that are leveraged for ion or small molecule transport. Ultraviolet–visible–near-infrared absorbance spectroscopy and electron paramagnetic spectroscopy showcase the interconversion between acidic (conductive) and basic (insulating) forms of these macrocycles and how charge carriers are formed through protonation, giving rise to the experimentally observed high electrical conductivity.
We advance the chemistry of apical chlorine substitution in the 2D superatomic semiconductor Re6Se8Cl2 to build functional and atomically precise monolayers on the surface of the 2D superatomic ...Re6Se8 substrate. We create a functional monolayer by installing surface (2,2′-bipyridine)-4-sulfide (Sbpy) groups that chelate to catalytically active metal complexes. Through this reaction chemistry, we can create monolayers where we can control the distribution of catalytic sites. As a demonstration, we create highly active electrocatalysts for the oxygen evolution reaction using monolayers of cobalt(acetylacetonate)2bipyridine. We can further produce a series of catalysts by incorporating organic spacers in the functional monolayers. The structure and flexibility of the surface linkers can affect the catalytic performance, possibly by tuning the coupling between the functional monolayer and the superatomic substrate. These studies establish that the Re6Se8 sheet behaves as a chemical pegboard: a surface amenable to geometrically and chemically well-defined modification to yield functional monolayers, in this case catalytically active, that are atomically precise. This is an effective method to generate diverse families of functional nanomaterials.
Conjugated molecular wires of rhenium bipyridine complexes were grown on flexible, lightweight, carbon-cloth electrodes through reductive diazonium electropolymerization. CO2 electrolysis studies ...reveal rapid (k cat ∼ 40 s–1) and selective (Faradaic efficiency >99%) conversion to CO with turnover numbers (TON) per rhenium site reaching ∼290 000 and catalytic currents (i cat) > 10 mA/cm2. This represents over an 80-fold increase in activity relative to our prior graphite systems and an ∼25-fold increase relative to the highest-performing immobilized rhenium bipyridine catalyst to date under analogous electrolysis conditions while maintaining prolonged activity. The high activity of these electrodes is explained by a mechanism initiated via electrochemical charging of the π-conjugated backbone followed by anion dissociation, CO2 coordination, and protonation. As numerous metal-bipyridine complexes are known for a broad scope of electrocatalytic transformations, these integrated carbon-cloth devices are anticipated to serve as a platform for future studies.
The solar-driven conversion of CO2 to value-added products provides a promising route for solar energy storage and atmospheric CO2 remediation. In this report, a variety of supporting electrode ...materials were successfully modified with a 2,2′-bipyridine-5,5′-bis(diazonium) rhenium complex through a surface-localized electropolymerization method. Physical characterization of the resulting multilayer films confirms that the coordination environments of the rhenium bipyridine tricarbonyl sites are preserved upon immobilization and that the polymerized catalyst moieties exhibit long-range structural order with uniform film growth. UV–vis studies reveal additional absorption bands in the visible region for the polymeric films that are not present in the analogous rhenium bipyridine complexes. Electrochemical studies with modified graphite rod electrodes show that the electrocatalytic activity of these films increases with catalyst loading up to an optimal value, beyond which electron and mass transport through the material become rate-limiting. Electrocatalytic studies performed at −2.25 V vs Fc/Fc+ for 2 h reveal CO production with faradaic efficiencies and turnover numbers up to 99% and 3606, respectively. Photocatalytic studies of the modified TiO2 devices demonstrate enhanced activity at low catalyst loadings, with turnover numbers up to 70 during 5 h of irradiation.
PDF
