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Titanium dioxide (TiO2) is an exceptional compound with unique optical properties, which have been intensively used for applications in photocatalysis. Recent studies show that Cu5 atomic quantum clusters (AQCs) could facilitate visible light absorption and enhance the photocatalytic properties of rutile TiO2 by creating mid-gap states. In this work, to move the theory of these catalysts closer to the experiment, we investigate the electronic structures of Cu5 adsorbed on a perfect and reduced rutile TiO2 surface in the absence and presence of silicate SiO32− ions, which are introduced for the purification of Cu5 AQCs. Encouragingly, our DFT simulations predict that the presence of SiO32− does not reduce the gap states of the Cu5@TiO2 composite and could even enhance them by shifting more states into the band gap. Our results also demonstrate that the polarons created by oxygen vacancies (Ov) and Cu5 coexist within the band gap of TiO2. Indeed an Ov behaves like a negative gate on the electronic states located on the AQCs, thereby shifting states out of the valence band into the band gap, which could lead to enhanced photocatalytic performance. [ABSTRACT FROM AUTHOR]

Sorting out organic molecules with high thermopower is essential for understanding molecular thermoelectrics. The intermolecular coupling offers a unique chance to enhance the thermopower by tuning the bandgap structure of molecular devices, but the investigation of intermolecular coupling in bulk materials remains challenging. Herein, we investigated the thermopower of diketopyrrolopyrrole (DPP) cored single-molecule junctions with different coupling strengths by varying the packing density of the self-assembled monolayers (SAM) using a customized scanning tunneling microscope break junction (STM-BJ) technique. We found that the thermopower of DPP molecules could be enhanced up to one order of magnitude with increasing packing density, suggesting that the thermopower increases with larger neighboring intermolecular interactions. The combined density functional theory (DFT) calculations revealed that the closely-packed configuration brings stronger intermolecular coupling and then reduces the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, leading to an enhanced thermopower. Our findings offer a new strategy for developing organic thermoelectric devices with high thermopower.

Transcribing quantum effects from lower to higher dimensions is a complex yet intriguing area of research. Coulomb blockade (CB), a fundamental quantum phenomenon, is commonly observed in low-dimensional materials like quantum dots (QDs) at extremely low temperatures. This behavior shows promise for the development of high-performance memory and thermoelectric devices. However, when transitioning to larger dimensions, such as arrays at room temperature, the CB effect is hindered by thermal fluctuations and structural inconsistencies. This study presents a thorough examination of electron transport through PbS QDs using a blend of experimental and theoretical methods. By creating a sizable parallel array of QDs immobilized on self-assembled monolayers (SAMs) and employing single-layer graphene (SLG) as the top electrode, we were able to maintain the CB effect at room temperature on a device scale. Additionally, a device with a top gate structure was designed to precisely regulate the energetic position of quantum states in relation to the Fermi level of the electrode. By utilizing ultra-small QDs (typically 2 nm in size), we successfully sustained the CB effect at room temperature. To investigate the impact of structural uncertainties, we combined density-functional theory and quantum transport theory to comprehensively analyze the quantum transport properties of QDs bound with SAMs across various facets. This enabled us to establish a correlation between these structural variations and the experimental data distribution. [ABSTRACT FROM AUTHOR]

In the cross‐plane single‐molecule junctions, the correlation between molecular aromaticity and conductance remained puzzling. Cross‐plane break junction (XPBJ) provides new insight into understanding the role of aromaticity and conjugation to molecules on charge transport through the planar molecules. In this work, we investigated the modulation of cross‐plane charge transport in pyrene derivatives by hydrogenation and substituents based on the XPBJ method that differs from those used in‐plane transport. We measured the electrical conductance of the hydrogenated derivatives of the pyrenes and found that hydrogenation reduces conductance, and the fully hydrogenated molecule has the lowest conductance. Conductance of pyrene derivatives increased after substitution by both electron‐donating and electron‐withdrawing groups. By calculating, the trend in decreased conductance of hydrogenated pyrene was found to be consistent with the change in aromaticity. Electron‐withdrawing substituents reduce the aromaticity of the molecule and narrow the HOMO‐LUMO gap, while electron‐donating groups increase the aromaticity but also narrow the gap. Our work reveals the potential of fine‐tuning the structure of the pyrene molecule to control the cross‐plane charge transport through the single‐molecule junctions. [ABSTRACT FROM AUTHOR]

There are several binding groups used within molecular electronics for anchoring molecules to metal electrodes (e.g., R−SMe, R−NH2, R−CS2−, R−S−). However, some anchoring groups that bind strongly to electrodes have poor/unknown stability, some have weak electrode coupling, while for some their binding motifs are not well defined. Further binding groups are required to aid molecular design and to achieve a suitable balance in performance across a range of properties. We present an in‐depth investigation into the use of carbodithioate esters as contact groups for single‐molecule conductance measurements, using scanning tunnelling microscopy break junction measurements (STM‐BJ) and detailed surface spectroscopic analysis. We demonstrate that the methyl carbodithioate ester acts as an effective contact for gold electrodes in STM‐BJ measurements. Surface enhanced Raman measurements demonstrate that the C=S functionality remains intact when adsorbed on to gold nanoparticles. A gold(I) complex was also synthesised showing a stable C=S→AuI interaction from the ester. Comparison with a benzyl thiomethyl ether demonstrates that the C=S moiety significantly contributes to charge transport in single‐molecule junctions. The overall performance of the CS2Me group demonstrates it should be used more extensively and has strong potential for the fabrication of larger area devices with long‐term stability. [ABSTRACT FROM AUTHOR]

This study highlights a novel strategy for tuning the electrical conductance of single molecules by cross linking the molecules to form a dimer. By studying the electrical conductance of dimers formed by cross linking OPE monomers, we demonstrate that the appearance of destructive or constructive quantum interference in cross-linked OPE-based dimers is independent of the nature of the molecular cross link. Instead, the type of the interference is controlled by the connectivity to external electrodes and is determined by the presence or otherwise of meta-connected phenyl rings in the transport path. This is expected to be an important design feature, when synthesising molecules with cross links of different stiffnesses for thermoelectric energy harvesting, since it shows that the stiffness (and hence phonon transport properties) can be tuned without affecting the nature of the electronic quantum interference. [ABSTRACT FROM AUTHOR]

Organic thin films composed of highly ordered molecular arrays hold tremendous potential for thermoelectric energy harvesting. In comparison to metal–thiolate arrays formed through covalent bonding, molecular arrays bound to graphene substrates via non-covalent interactions exhibit superior thermoelectric behavior. Recent studies have explored the thermoelectric properties of non-conjugated junctions utilizing graphene as a substrate. However, for energy-harvesting purposes, conjugated oligo-aromatic molecules with narrower HOMO–LUMO gaps are more desirable. The step-wise assembly strategy, which involves using a zinc-centered porphyrin to form a footpad first and subsequently binding the molecular backbones to the regularly arranged zinc centers in the footpad, has been reported as an effective approach for growing conjugated molecular backbone arrays, with minimal intermolecular effects on various types of substrates. In this study, we employ this strategy to fabricate aromatic molecular arrays on graphene substrates. Initially, a zinc-centered porphyrin layer is immobilized onto the graphene substrate through π–π stacking interactions. Subsequently, a conjugated pyridine backbone is coordinated to the zinc tetraphenylporphyrin (ZnTPP). Due to the substantial footprint of ZnTPP, this sequential assembly method effectively separates the molecular backbones and prevents smearing of the density of states arising from intermolecular interactions. Consequently, a significant enhancement in thermopower is achieved. Our findings present a novel approach for designing high-efficiency thermoelectric materials, resulting in a Seebeck coefficient of approximately 51 μV K−1. This value surpasses the majority of reported Seebeck coefficients for organic molecular junctions. [ABSTRACT FROM AUTHOR]

Quantum interference (QI) plays a crucial role in determining the charge transport in molecular devices. In this work, the efficient modulation of QI in meta‐phenylene ethylene oligomer molecular devices by a double N‐substitution strategy is demonstrated. By altering the positions of two N atoms in the central ring with respect to the connecting sites, the molecular conductance can be tuned by more than one order of magnitude. Theoretical analysis, including magic ratio theory, orbital rule, and transmission simulations, reveals how the two N atoms synergistically modulate the molecule conductance between destructive QI and constructive QI states. Remarkably, addition of a second N atom does not simple reinforce the effect of the first; in contrast, it may completely cancel the effect of the first. Understanding the complex electronic interplay between the two N atoms in double N‐substituted molecules paves a path toward utilization of heterocyclic aromatic hydrocarbons in molecular electronics. [ABSTRACT FROM AUTHOR]

Correction for 'Tuning the electrical conductance of oligo(phenylene-ethynylene) derivatives-PbS quantum-dot bilayers' by Ali Ismael et al., J. Mater. Chem. C, 2024, 12, 14004–14012, https://doi.org/10.1039/D4TC00478G. [ABSTRACT FROM AUTHOR]

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