Single‐molecule junctions and self‐assembled monolayer junctions are attractive architectures for thermoelectric devices. However, given the poor thermoelectric performance of organic molecules ...investigated so far, molecules characterized by high conductance and Seebeck coefficient values are desired to be explored. Metal complexes are promising possible active components of high‐performance thermoelectric devices given that metal‐ligand combinations and functions can be made to vary to modulate the transmission functions, thus strongly influencing conductance and Seebeck coefficient. In this concept article are described recent studies wherein thermoelectric measurements were conducted on metal complex junctions. Furthermore, the potential for the use of the junctions in thermoelectric devices is discussed.
Molecular junctions, which are composed of metal electrode‐molecule‐metal electrode structures, are attractive components of thermoelectric devices. In this Concept article, we discuss recent thermoelectric studies on metal complex junctions. Furthermore, the potential utility of functional metal complex junctions for thermoelectric devices is also described.
The vibration-based electret generators (EGs) for energy harvesting have been extensively studied because they can obtain electrical energy from ambient vibrations. EGs exhibit a sandwich structure ...of electrodes surrounding an air gap and an electret, which is a dielectric material with a quasi-permanent electrical charge or dipole polarisation. Various charging processes have been developed because the surface charge density (σ) of the electret determines the output power of the device. However, such processes are considered to constitute a key productivity-limiting factor from the mass production viewpoint, making their simplification or elimination a highly desired objective. Herein, a model EG that does not require any charging process by utilising the spontaneous orientation polarisation of 1,3,5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi) is demonstrated. The surface potential (V
) of an evaporated TPBi film has reached 30.2 V at a film thickness of 500 nm without using a charging process. The estimated σ of 1.7 mC m
is comparable with that obtained using a conventional polymer-based electret after charging. Furthermore, V
is considerably stable in environmental conditions; thus, TPBi can be considered to be "self-assembled" electret (SAE). Application of SAE leads to developing an EG without requiring the charging process.
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•Single-molecule conductance of MMM (metal–molecule-metal) junctions consisting of mono- and oligo-nuclear trans-Ru(phosphine)4-acetylide linkages has been summarized and compared ...with relevant organic junctions.•Single-molecule conductance mainly obtained by the STM-BJ (break junction) technique has been interpreted in terms of DFT and DFT-NEGF (non-equilibrium Green function) calculations, which have revealed that energy alignment between the molecules and electrodes is the key for higher conductance.•By tuning the components of the organoruthenium junctions long range carrier transport up to ∼ 4 nm with 10−2G0 level conductance has been achieved.
MMM (metal–molecule-metal) junction exhibiting wire-like functions is an essential component of molecular circuit/electronics. Herein reviewed are recent advances in the study of single molecule conductance behavior of MMM junctions based on carbon-rich organometallics, with a particular focus on the mono- and oligo-nuclear, linear trans-Ru(phosphine)4-acetylide linkages. The conductance of MMM junctions determined by the STM-BJ (scanning tunneling microscopy-break junction) method has drastically improved by energy alignment between the wire part and the electrodes by tuning the components of the organometallic wire part (e.g. metal, ligand, organic linker, and anchor). The efficient energy alignment of carbon-rich organometallic systems arises from (i) the contribution of the metal d-electrons being higher in energy than the 2 s- and 2p-electrons used for purely organic junctions and much closer to the d-electron levels of metal electrodes and (ii) covalent interactions not only between anchor and electrode but also between metal and organic linker. As a result, the excellent long range carrier transport up to ∼ 4 nm with 10−2 G0 level conductance has been achieved. Conductance behavior of MMM junctions has been successfully interpreted in terms of transmission spectra obtained by the hybrid DFT-NEGF (non-equilibrium Green function) calculations.
•Alcohol oxidase of a fungus Pyricularia oryzae (PoAlcOX) contains a WSC domain.•Deletion of the WSC domain does not affect oxidation of alcohols by PoAlcOX.•PoAlcOX binds to xylans and fungal ...chitin/β-1,3-glucan.•Deletion of the WSC domain results in loss of the carbohydrate-binding property.
The cell wall integrity and stress response component (WSC) domain was first described in the Wsc-family protein of the yeast Saccharomyces cerevisiae, and later found in diverse eukaryotic organisms. Due solely to their presence in the Wsc-family proteins working as a plasma membrane sensor for surface stress and in a fungal β-1,3-exoglucanse, WSC domains have been presumed to possess carbohydrate-binding property without any experimental evidence. Aiming at elucidation of function(s) of WSC domains, we characterized a WSC domain-containing alcohol oxidase from the rice blast pathogen Pyricularia oryzae (PoAlcOX). Recombinant PoAlcOX produced with Pichia pastoris showed alcohol oxidase activity toward a wide range of substrates including two aliphatic alcohols, a branched-chain alcohol, a diol, and a polyol. Deletion of the WSC domain virtually unaffected oxidation of these substrates by PoAlcOX, indicating that the domain makes no contribution to the catalytic activity. In analogy to some carbohydrate-binding modules, we inferred that the WSC domain plays a role in protein anchoring, and evaluated binding capability of PoAlcOX to a set of polysaccharide components of fungal and plant cell walls. This revealed that PoAlcOX binds to xylans and fungal chitin/β-1,3-glucan in the WSC domain-dependent manner, demonstrating for the first time the carbohydrate-binding property of the domain. Additionally, we provide evidence that PoAlcOX immobilized on birch wood xylan retains the catalytic activity. Overall, the data we collected suggest that the role of the WSC domain of PoAlcOX is not recognition of substrates but attaching the enzyme to plant and/or fungal cell wall.
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•Redox chemistry of mono- and di-nuclear radical species of Fe and Ru.•Difference of location of the radical center, on the metal centers or on the ligand.•Delocalized dinuclear ...species may work as molecular wire.
Redox chemistry of d6 iron(II) and ruthenium(II) complexes has been studied extensively due to the interesting reactivity of mononuclear radical species and the charge-delocalized properties of dinuclear mixed-valence (MV) complexes. In particular, organometallic dinuclear MV systems show long-range charge-delocalized behavior, and their properties can be modified by the choice of the metal (M) and the bridging ligand (BL). Here we review mono- and di-nuclear radical species having CP2M and CPM(dppe) fragments (CP = η5-C5H5 or η5-C5Me5; M = Fe, Ru) as the redox centers. Although the Fe and Ru species are frequently isostructural, the electronic structures of them are considerably different. Radical center tends to localize rather on the metal center and the ligand part in the Fe and Ru complexes, respectively. For mononuclear species, the Ru complexes exhibit reactivity at the ligand to undergo radical coupling, whereas the Fe complexes may stay as monomeric radical species. For dinuclear complexes, the radical center of mixed-valence diiron species rather localizes on the metal center, while that of the diruthenium analogues tends to localize on the BL. The difference could be ascribed to reorganization caused by the electron transfer, and the extent of the contribution of the BL-localized state can be estimated by the difference between the νmax values for an Fe complex and its Ru derivative (Δνmax(Ru-Fe)).
Spontaneous orientation polarization (SOP) of amorphous organic semiconducting films has attracted much attention because of its frequent observation in common organic light-emitting diodes (OLEDs) ...and potential influences on the device properties of OLEDs. On the other hand, the formation mechanism of SOP has been controversial for a long time, ever since its discovery in 2002. Recently, the formation mechanism of SOP was explained in terms of the surface equilibration mechanism of vapor-deposited glasses, and the understanding of SOP has progressed significantly. Based on the improved understanding, some active control methods of SOP have been demonstrated and further influences on the device performance of OLEDs were revealed, suggesting that higher efficiency can be achieved by managing SOP properly. Furthermore, some applications of SOP have also been proposed, such as a self-assembled electret and a tool for evaluating materials properties. In this paper, recent progress in the understanding of SOP and its applications to devices are reviewed.
•Recent progress in understanding of spontaneous orientation polarization (SOP) in organic semiconducting films is reviewed.•Formation mechanism and active control methods of SOP are discussed.•Influences of SOP on the device performance of organic light-emitting diodes are discussed.•Applications of SOP are introduced.
To explore new cavity functions, we herein employed cis‐trans stereoisomers with a N=N, C=C, or C=N unit as guest indicators for a polyaromatic capsule. Thanks to the rigid, spherical cavity with a ...diameter of ∼1 nm, azobenzene and stilbene derivatives are quantitatively encapsulated by the capsule with 100 % cis‐selectivity in water. The isomerization of the cis‐azo compound is suppressed against heat and light in the cavity, due to the confinement effect. Furthermore, C,N‐diphenyl imine derivatives are quantitatively encapsulated by the capsule in water and adopt an otherwise unstable cis‐form. The polyaromatic cavity suppresses the hydrolysis of the imines in water, even at elevated temperature, due to the shielding effect. Accordingly, the properties of the cis‐trans isomers could be largely altered through supramolecular manipulation.
Thanks to a polyaromatic capsule, an azobenzene derivative is quantitatively encapsulated by the spherical cavity with 100 % cis‐selectivity. The cis‐to‐trans isomerization is suppressed against heat and light due to the confined cavity effect. C,N‐diphenyl imines are also encapsulated by the capsule and adopt an otherwise unstable cis‐form. The cavity suppresses their hydrolysis in water due to the shielding effect.
Recent developments of single‐molecule conductance measurements allow us to understand fundamental conducting properties of molecular wires. While a wide variety of organic molecular wires have been ...studied so far, inorganic and organometallic molecular wires have received much less attention. However, molecular wires with transition‐metal atoms show interesting features and functions distinct from those of organic wires. These properties originate mainly from metal–ligand dπ–pπ interactions and metal–metal d–d interactions. Thanks to the rich combination of metal atoms and supporting ligands, frontier orbital energies of the molecular wires can be finely tuned to lead to highly conducting molecular wires. Moreover, the unique electronic structures of metal complexes are susceptible to subtle environmental changes, leading to potential functional molecular devices. This article reviews recent advances in the single‐molecule conductance study of inorganic and organometallic molecular wires.
Recent developments for single‐molecule conductance measurements allow to access fundamental properties of molecular wires in metal–molecule–metal junctions. This Concept article presents a review of advances in recent single molecule conductance studies with metal complexes.
Anisotropic contraction of a spherical polyaromatic capsule was demonstrated through simple meta-to-ortho modification of the bent polyaromatic ligands. The resultant capsule, composed of two metal ...ions and four ortho-substituted ligands, possesses a spheroidal cavity (1.1 nm × 1.5 nm × 1.5 nm) fully encircled by a polyaromatic framework. One large planar or bowl-shaped molecule (e.g., porphine or sumanene) is quantitatively bound by the capsule, in which the cavity-induced compression effect causes the acceleration of the bowl-to-bowl inversion of sumanene. Temperature-dependent 1H NMR analysis revealed that the activation energy of the inversion decreases greatly (ΔG ⧧ = −2.8 kcal mol–1 at 318 K) upon encapsulation, whereas the opposite effect was observed in the spherical cavity of the previous polyaromatic capsule.
Herein, we report the synthesis and electrochemical and photophysical properties of aromatic hydrocarbons having one or two dimesitylborylethynyl peripherals. The mono‐ (1) and diboryl compounds (2), ...readily prepared by nucleophilic substitution reaction, are fairly stable to air and moisture in the solid state. The inserted ethynediyl (C≡C) spacer cancels the steric hindrance between the bulky dimesitylboryl groups and aromatic rings, leading to effective π conjugation over the B−C≡C−Ar linkages, as revealed by cyclic voltammetry. Despite the small structural differences, the photophysical properties of the benzene, naphthalene, and anthracene derivatives are different. Virtually no emission was observed from the benzene derivatives, whereas the anthracene derivatives emitted with high quantum yields both in solution and in the solid state. Notably, the naphthalene derivatives showed aggregation‐induced emission behavior. Unlike the common sterically congested triarylborane derivatives reported so far, the anthracene derivatives showed π–π*‐type absorption and emission bands, which derive from efficient intramolecular orbital interactions between the boron centers and anthracene moieties, as supported by DFT calculations. As a result, the dimesitylborylethynyl substituents effectively lower the LUMO levels of the aromatic hydrocarbon parts, whereas the HOMO levels are almost unaffected, thereby leading to materials with controllable HOMO–LUMO gaps.
Spaced out! Aromatic hydrocarbons having one or two dimesitylborylethynyl peripherals show rich photophysical and electrochemical properties. Unlike common sterically congested triarylboranes, the inserted ethynediyl spacer cancels the steric hindrance between the bulky dimesitylboryl groups and aromatic rings, leading to effective π conjugation over the B−C≡C−Ar linkages. Despite the small structural differences, the benzene, naphthalene, and anthracene derivatives show distinct photophysical behaviors (see scheme).
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