Chemical pressure-induced PtIII-I Mott-Hubbard nanowire, [Pt(en)2I](Asp-Cn)2·H2O (13 ≤ n), detected via polarized infrared spectroscopy.

The electronic states of iodo-bridged platinum nanowire complexes have been studied using polarized FT-IR spectroscopy. The N-H symmetrical stretching mode was found to be highly sensitive to the electronic states, distinguishing mixed-valence (MV) and averaged-valence (AV) states. The first Pt(III) nanowire complexes have been realized by the chemical pressures of the counter-anions.

Asymmetrically Functionalized Electron-Deficient π-Conjugated System for Printed Single-Crystalline Organic Electronics.

Large-area single-crystalline thin films of n-type organic semiconductors (OSCs) fabricated via solution-processed techniques are urgently demanded for high-end electronics. However, the lack of molecular designs that concomitantly offer excellent charge-carrier transport, solution-processability, and chemical/thermal robustness for n-type OSCs limits the understanding of fundamental charge-transport properties and impedes the realization of large-area electronics. The benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) π-electron system with phenethyl substituents (PhC2 -BQQDI) demonstrates high electron mobility and robustness but its strong aggregation results in unsatisfactory solubility and solution-processability. In this work, an asymmetric molecular design approach is reported that harnesses the favorable charge transport of PhC2 -BQQDI, while introducing alkyl chains to improve the solubility and solution-processability. An effective synthetic strategy is developed to obtain the target asymmetric BQQDI (PhC2 -BQQDI-Cn ). Interestingly, linear alkyl chains of PhC2 -BQQDI-Cn (n = 5-7) exhibit an unusual molecular mimicry geometry with a gauche conformation and resilience to dynamic disorders. Asymmetric PhC2 -BQQDI-C5 demonstrates excellent electron mobility and centimeter-scale continuous single-crystalline thin films, which are two orders of magnitude larger than that of PhC2 -BQQDI, allowing for the investigation of electron transport anisotropy and applicable electronics.

Dual-radical-based molecular anisotropy and synergy effect of semi-conductivity and valence tautomerization in a photoswitchable coordination polymer.

Organic radicals are widely used as linkers or ligands to synthesize molecular magnetic materials. However, studies regarding the molecular anisotropies of radical-based magnetic materials and their multifunctionalities are rare. Herein, a photoisomerizable diarylethene ligand was used to form {[CoIII(3,5-DTSQ·-)(3,5-DTCat2-)]2(6F-DAE-py2)}·3CH3CN·H2O (o-1·3CH3CN·H2O, 6F-DAE-py2 = 1,2-bis(2-methyl-5-(4-pyridyl)-3-thienyl)perfluorocyclopentene), a valence-tautomeric (VT) coordination polymer. We directly observed dual radicals for a single crystal using high-field/-frequency (∼13.3 T and ∼360 GHz) electron paramagnetic resonance (EPR) spectroscopy along the c-axis, which was further confirmed by angle-dependent Q-band EPR spectroscopy. Moreover, a conductive anomaly close to the VT transition temperature was observed only when probes were attached at the ab plane of the single crystal, indicative of synergy between valence tautomerism and conductivity. Structural anisotropy studies and density functional theory (DFT) calculations revealed that this synergy is due to electron transfer associated with valence tautomerism. This study presents the first example of dual-radical-based molecular anisotropy and charge-transfer-induced conductive anisotropy in a photoswitchable coordination polymer.

Individual and synergetic charge transport properties at the solid and electrolyte interfaces of a single ultrathin single crystal of organic semiconductors.

The chemical structures and morphologies of organic semiconductors (OSCs) and gate dielectrics have been widely investigated to improve the electrical performances of organic thin-film transistors (OTFTs) because the charge transport therein is a phenomenon at the semiconductor-dielectric interfaces. Here, solid and ionic gel gate dielectrics were adopted on the lower and upper surfaces, respectively, of a single, two molecule-thick single crystals of p-type OSCs to study the charge transport properties at individual interfaces between the morphologically compatible OSC surface and different gate dielectrics. Using the four-probe method, the solid and ionic gel interfaces were found to exhibit hole mobilities of 9.3 and 2.2 cm2 V-1 s-1, respectively, which revealed the crucial impact of the gate dielectric materials on the interfacial charge transport. Interestingly, when gate biases are applied through both dielectrics, i.e., under the solid/ionic gel dual-gate transistor operation, the hole mobility at the solid gate interface is improved up to 14.7 cm2 V-1 s-1, which is 1.5 times greater than that assessed without the ionic gel gate. This improvement can be attributed to the electric double layer formed at the ionic gel/uniform crystal surface, which provides a close-to-ideal charge transport interface through dramatic trap-filling. Therefore, the present dual-gate transistor technique will be promising for investigating the intrinsic charge-transport capabilities of OSCs.

Crown ether salt-doped ladder-type conducting polymers for air-stable n-type thermoelectric materials.

Thermoelectric energy harvesters based on p- and n-type organic semiconductors are in high demand, while the air stability of n-type devices has long been a challenge. Here, we demonstrate that supramolecular salt-functionalized n-doped ladder-type conducting polymers exhibit excellent stability in the presence of dry air.

Electron-Deficient Benzo[de]isoquinolino[1,8-gh]quinoline Diamide π-Electron Systems.

Synthetically versatile electron-deficient π-electron systems are urgently needed for organic electronics, yet their design and synthesis are challenging due to the low reactivity from large electron affinities. In this work, we report a benzo[de]isoquinolino[1,8-gh]quinoline diamide (BQQDA) π-electron system. The electron-rich condensed amide as opposed to the generally-employed imide provides a suitable electronic feature for chemical versatility to tailor the BQQDA π-electron system for various electronic applications. We demonstrate an effective synthetic method to furnish the target BQQDA parent structure, and highly selective functionalization can be performed on bay positions of the π-skeleton. In addition, thionation of BQQDA can be accomplished under mild conditions. Fine-tuning of fundamental properties and supramolecular packing motifs are achieved via chemical modifications, and the cyanated BQQDA organic semiconductor demonstrates a high air-stable electron-carrier mobility.

Myeloid cell-specific ablation of Runx2 gene exacerbates post-infarct cardiac remodeling.

Runt-related transcription factor 2 (Runx2), a regulator of osteoblast differentiation, is pathologically involved in vascular calcification; however, the significance of Runx2 in cardiac homeostasis remains unclear. Here, we investigated the roles of Runx2 in cardiac remodeling after myocardial infarction (MI). The expression of Runx2 mRNA and protein was upregulated in murine hearts after MI. Runx2 was expressed in heart-infiltrating myeloid cells, especially in macrophages, at the border zone of post-infarct myocardium. To analyze the biological functions of Runx2 in cardiac remodeling, myeloid cell-specific Runx2 deficient (CKO) mice were exposed to MI. After MI, ventricular weight/tibia length ratio was increased in CKO mice, concomitant with severe cardiac dysfunction. Cardiac fibrosis was exacerbated in CKO mice, consistent with the upregulation of collagen 1a1 expression. Mechanistically, immunohistochemical analysis using anti-CD31 antibody showed that capillary density was decreased in CKO mice. Additionally, conditioned culture media of myeloid cells from Runx2 deficient mice exposed to MI induced the tube formation of vascular endothelial cells to a lesser extent than those from control mice. RNA-sequence showed that the expression of pro-angiogenic or anti-angiogenic factors was altered in macrophages from Runx2-deficient mice. Collectively, Runx2+ myeloid cells infiltrate into post-infarct myocardium and prevent adverse cardiac remodeling, at least partially, by regulating endothelial cell function.

Mixed-Orbital Charge Transport in N-Shaped Benzene- and Pyrazine-Fused Organic Semiconductors.

The hole-carrier transport of organic semiconductors is widely known to occur via intermolecular orbital overlaps of the highest occupied molecular orbitals (HOMO), though the effect of other occupied molecular orbitals on charge transport is rarely investigated. In this work, we first demonstrate evidence of a mixed-orbital charge transport concept in the high-performance N-shaped decyl-dinaphtho[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (C10-DNBDT-NW), where electronic couplings of the second HOMO (SHOMO) and third HOMO (THOMO) also contribute to the charge transport. We then present the molecular design of an N-shaped bis(naphtho[2',3':4,5]thieno)[2,3-b:2',3'-e]pyrazine (BNTP) π-electron system to induce more pronounced mixed-orbital charge transport by incorporating the pyrazine moiety. An effective synthetic strategy for the pyrazine-fused extended π-electron system is developed. With substituent engineering, the favorable two-dimensional herringbone assembly can be obtained with BNTP, and the decylphenyl-substituted BNTP (C10Ph-BNTP) demonstrates large electronic couplings involving the HOMO, SHOMO, and THOMO in the herringbone assembly. C10Ph-BNTP further shows enhanced mixed-orbital charge transport when the electronic couplings of all three occupied molecular orbitals are taken into consideration, which results in a high hole mobility up to 9.6 cm2 V-1 s-1 in single-crystal thin-film organic field-effect transistors. The present study provides insights into the contribution of HOMO, SHOMO, and THOMO to the mixed-orbital charge transport of organic semiconductors.

Macro- and atomic-scale observations of a one-dimensional heterojunction in a nickel and palladium nanowire complex.

The creation of low-dimensional heterostructures for intelligent devices is a challenging research topic; however, macro- and atomic-scale connections in one-dimensional (1D) electronic systems have not been achieved yet. Herein, we synthesize a heterostructure comprising a 1D Mott insulator [Ni(chxn)2Br]Br2 (1; chxn = 1R-2R-diaminocyclohexane) and a 1D Peierls or charge-density-wave insulator [Pd(chxn)2Br]Br2 (2) using stepwise electrochemical growth. It can be considered as the first example of electrochemical liquid-phase epitaxy applied to molecular-based heterostructures with a macroscopic scale. Moreover, atomic-resolution scanning tunneling microscopy images reveal a modulation of the electronic state in the heterojunction region with a length of five metal atoms (~ 2.5 nm), that is a direct evidence for the atomic-scale connection of 1 and 2. This is the first time that the heterojunction in the 1D chains has been shown and examined experimentally at macro- and atomic-scale. This study thus serves as proof of concept for heterojunctions in 1D electronic systems.

Thermally induced electron-hole dissociation dynamics in quasi-one-dimensional bromo-bridged palladium(III) Mott-insulator [Pd(en)2Br](Suc-Cn)2·H2O (Cn-Y = dialkylsulfosuccinate; n = 5 and 6).

Current-voltage characteristics and dielectric properties were studied in bromo-bridged one-dimensional compounds, [Pd(en)2Br](Suc-C5)2·H2O, exhibiting mixed-valence and averaged valence (MV-AV) phase transition. In the AV phase, clear nonlinear current-voltage characteristics were observed. This phenomenon was explained by the thermally induced electron-hole separation assisted by an electric field. This mechanism was supported by the dielectric properties of [Pd(en)2Br](Suc-Cn)2·H2O (n = 5 and 6).

Nitrogen-Containing Perylene Diimides: Molecular Design, Robust Aggregated Structures, and Advances in n-Type Organic Semiconductors.

ConspectusOrganic semiconductors (OSCs) have attracted much attention because of their potential applications for flexible and printed electronic devices and thus have been extensively investigated in a variety of research fields, such as organic chemistry, solid-state physics, and device physics and engineering. Organic thin-film transistors (OTFTs), a class of OSC-based devices, have been expected to be an alternative of silicon-based metal oxide semiconductor field-effect transistors (MOSFETs), which is the indispensable element for most of the current electronic devices. However, the noncovalently aggregated, van der Waals solid nature of the OSCs, by contrast to covalently bound silicon, conventionally exhibits lower carrier mobilities, limiting the practical applications of OTFTs. In particular, electron-transporting (i.e., n-type) OSCs lag behind their hole-transporting (p-type) counterparts in carrier mobility and ambient stability as OTFTs. This is primarily because of the difficulty in achieving compatibility between the aggregated structure exhibiting excellent carrier mobility and that with enough electron affinity. Recent understandings of carrier transport in OSCs explain that large and two-dimensionally isotropic transfer integrals coupled with small fluctuations are crucial for high carrier mobilities. In addition, from a practical point of view, the compatibility with practical device processes is highly required. Rational molecular design principles, therefore, are still demanded for developing OSCs and OTFTs toward high-end device applications.Herein, we will show our recent progress in the development of n-type OSCs with the key π-electron core (π-core) of benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) on the basis of single-crystal OTFT technologies and the band-transport model enabled by two-dimensional molecular packing arrangements. The critical point is the introduction of electronegative nitrogen atoms into the π-core: the nitrogen atoms in BQQDI not only deepen the molecular orbital energies but also allow hydrogen-bonding-like attractive intermolecular interactions to control the aggregated structures, unlike the conventional role of the nitrogen introduced into OSCs only for the former role. Hence, the BQQDI analogues exhibit air-stable OTFT behavior and two-dimensional brickwork packing structures. Specifically, phenethyl-substituted analogue (PhC2-BQQDI) has been shown as the first principal BQQDI-based material, demonstrating solution-processable thin-film single crystals, fewer anisotropic transfer integrals, and an effective suppression of molecular motions, leading to band-like electron-transport properties and stress-durable n-channel OTFT performances, in conjunction with the support of computational calculations. Insights into more fundamental points of view have been found by side-chain derivatization and OTFT studies on polycrystalline and single-crystal films. We hope that this Account provides readers with new strategies for designing high-performance OSCs by two-dimensional control of the aggregated structures.

Strong and Atmospherically Stable Dicationic Oxidative Dopant.

Increasing the doping level of semiconducting polymer using strong dopants is essential for achieving good electrical conductivity. As for p-dopant, raising the electron affinity of a neutral compound through the dense introduction of electron-withdrawing group has always been the predominant strategy to achieve strong dopant. However, this simple and intuitive strategy faces extendibility, accessibility, and stability issues for further development. Herein, the use of dicationic state of tetraaryl benzidine (TAB2+ ) in conjunction with bis(trifluoromethylsulfonyl)imide anion (TFSI- ) as a strong and atmospherically stable p-dopant (TAB-2TFSI), for which the concept is hinted from a rapid and spontaneous dimerization of radical cation dopant, is demonstrated. TAB-2TFSI possesses a large redox potential such that it would have deteriorated when in contact with H2 O. However, no trace of degradation after 1 year of storage under atmospheric conditions is observed. When doping the state-of-the-art semiconducting polymer with TAB-2TFSI, a high doping level together with significantly enhanced crystallinity is achieved which led to an electrical conductivity as high as 656 S cm-1 . The concept of utilizing charged molecule as a dopant is highly versatile and will potentially accelerate the development of a strong yet stable dopant.

Role of Perfluorophenyl Group in the Side Chain of Small-Molecule n-Type Organic Semiconductors in Stress Stability of Single-Crystal Transistors.

Operational stability, such as long-term ambient durability and bias stress stability, is one of the most significant parameters in organic thin-film transistors (OTFTs). The understanding of such stabilities has been mainly devoted to energy levels of frontier orbitals, thin-film morphologies, and device configuration involving gate dielectrics and electrodes, whereas the roles of molecular and aggregated structural features in device stability are seldom discussed. In this Letter, we report a remarkable enhancement of operational stability, especially bias stress, of n-channel single-crystal OTFTs derived from a replacement of phenyl with perfluorophenyl groups in the side chain. Because of the several-molecule-thick single-crystal nature employed for the OTFTs, the crystal-surface properties are thought to be critical, where the surface structure composed of perfluorophenyl moieties could suppress interactions between environmental species and field-induced carriers owing to increased hydrophobicity and steric protection of π-conjugated units.

Surface Doping of Organic Single-Crystal Semiconductors to Produce Strain-Sensitive Conductive Nanosheets.

A highly periodic electrostatic potential, even though established in van der Waals bonded organic crystals, is essential for the realization of a coherent band electron system. While impurity doping is an effective chemical operation that can precisely tune the energy of an electronic system, it always faces an unavoidable difficulty in molecular crystals because the introduction of a relatively high density of dopants inevitably destroys the highly ordered molecular framework. In striking contrast, a versatile strategy is presented to create coherent 2D electronic carriers at the surface of organic semiconductor crystals with their precise molecular structures preserved perfectly. The formation of an assembly of redox-active molecular dopants via a simple one-shot solution process on a molecularly flat crystalline surface allows efficient chemical doping and results in a relatively high carrier density of 1013 cm-2 at room temperature. Structural and magnetotransport analyses comprehensively reveal that excellent carrier transport and piezoresistive effects can be obtained that are similar to those in bulk crystals.

Electronic excitation spectra of organic semiconductor/ionic liquid interface by electrochemical attenuated total reflectance spectroscopy.

The interface of organic semiconductor films is of particular importance with respect to various electrochemical devices such as transistors and solar cells. In this study, we developed a new spectroscopic system, namely electrochemical attenuated total reflectance ultraviolet (EC-ATR-UV) spectroscopy, which can access the interfacial area. Ionic liquid-gated organic field-effect transistors (IL-gated OFETs) were successfully fabricated on the ATR prism. Spectral changes of the organic semiconductor were then investigated in relation to the gate voltage application and IL species, and the magnitude of spectral changes was found to correlate positively with the drain current. Additionally, the Stark shifts of not only the organic semiconductor, but also of the IL on the organic semiconductor films were detected. This new method can be applied to other electrochemical devices such as organic thin film solar cells, in which the interfacial region is crucial to their functioning.

Approaching isotropic charge transport of n-type organic semiconductors with bulky substituents.

Benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) is an n-type organic semiconductor that has shown unique multi-fold intermolecular hydrogen-bonding interactions, leading to aggregated structures with excellent charge transports and electron mobility properties. However, the strong intermolecular anchoring of BQQDI presents challenges for fine-tuning the molecular assembly and improving the semiconducting properties. Herein, we report the design and synthesis of two BQQDI derivatives with phenyl- and cyclohexyl substituents (Ph-BQQDI and Cy6-BQQDI), where the two organic semiconductors show distinct molecular assemblies and degrees of intermolecular orbital overlaps. In addition, the difference in their packing motifs leads to strikingly different band structures that give rise to contrasting charge-transport capabilities. More specifically, Cy6-BQQDI bearing bulky substituents exhibits isotropic intermolecular orbital overlaps resulting in equal averaged transfer integrals in both π-π stacking directions, even when dynamic disorders are taken into account; whereas Ph-BQQDI exhibits anisotropic averaged transfer integrals in these directions. As a result, Cy6-BQQDI shows excellent device performances in both single-crystalline and polycrystalline thin-film organic field-effect transistors up to 2.3 and 1.0 cm2 V-1 s-1, respectively.

Coherent Electron Transport in Air-Stable, Printed Single-Crystal Organic Semiconductor and Application to Megahertz Transistors.

Organic semiconductors (OSCs) have attracted growing attention for optoelectronic applications such as field-effect transistors (FETs), and coherent (or band-like) carrier transport properties in OSC single crystals (SCs) have been of interest as they can lead to high carrier mobilities. Recently, such p-type OSC SCs compatible with a printing technology have been used to achieve high-speed FETs; therefore, developments of n-type counterparts may be promising for realizing high-speed complementary organic circuits. Herein, coherent electron transport properties in a printed SC of a state-of-the-art, air-stable n-type OSC, PhC2 -BQQDI, by means of variable-temperature gated Hall effect measurements and X-ray single-crystal diffraction analyses in conjunction with band structure calculations, are reported. Furthermore, the SC FET is tested for high-speed operations, which obtains a cutoff frequency of 4.3 MHz at an operation voltage of 20 V in air. Thus, PhC2 -BQQDI is shown as a new candidate for practical applications of SC-based, organic complementary devices.

Alkyl-Substituted Selenium-Bridged V-Shaped Organic Semiconductors Exhibiting High Hole Mobility and Unusual Aggregation Behavior.

Toward the development of high-performance organic semiconductors (OSCs), carrier mobility is the most important requirement for next-generation OSC-based electronics. The strategy is that OSCs consisting of a highly extended π-electron core exhibit two-dimensional (2D) aggregated structures to offer effective charge transport. However, such OSCs, in general, show poor solubility in common organic solvents, resulting in limited solution processability. This is a critical trade-off between the development of OSCs with simultaneous high carrier mobility and suitable solubility. To address this issue, herein, five-membered ring-fused selenium-bridged V-shaped binaphthalene with decyl substituents (C10-DNS-VW) is developed and synthesized by an efficient method. C10-DNS-VW exhibits significantly high solubility for solution processes. Notably, C10-DNS-VW forms a one-dimensional π-stacked packing motif (1D motif) and a 2D herringbone (HB) packing motif (2D motif), depending on the crystal growth condition. On the other hand, the fabrication of thin films by means of both solution process and vacuum deposition techniques forms only the 2D HB motif. External stress tests such as heating and exposure to solvent vapor indicated that 1D and 2D motifs could be synergistically induced by the total balance of intermolecular interactions. Finally, the single-crystalline films of C10-DNS-VW by solution process exhibit carrier mobility up to 11 cm2 V-1 s-1 with suitable transistor stability under ambient conditions for more than two months, indicating that C10-DNS-VW is one of the most promising candidates for breaking the trade-off in the field of solution-processed technologies.

Robust, high-performance n-type organic semiconductors.

Organic semiconductors (OSCs) are important active materials for the fabrication of next-generation organic-based electronics. However, the development of n-type OSCs lags behind that of p-type OSCs in terms of charge-carrier mobility and environmental stability. This is due to the absence of molecular designs that satisfy the requirements. The present study describes the design and synthesis of n-type OSCs based on challenging molecular features involving a π-electron core containing electronegative N atoms and substituents. The unique π-electron system simultaneously reinforces both electronic and structural interactions. The current n-type OSCs exhibit high electron mobilities with high reliability, atmospheric stability, and robustness against environmental and heat stresses and are superior to other existing n-type OSCs. This molecular design represents a rational strategy for the development of high-end organic-based electronics.

Damage-free Metal Electrode Transfer to Monolayer Organic Single Crystalline Thin Films.

Solution-processed organic thin film transistors (OTFTs) are an essential building block for next-generation printed electronic devices. Organic semiconductors (OSCs) that can spontaneously form a molecular assembly play a vital role in the fabrication of OTFTs. OTFT fabrication processes consist of sequential deposition of functional layers, which inherently brings significant difficulties in realizing ideal properties because underlayers are likely to be damaged by application of subsequent layers. These difficulties are particularly prominent when forming metal contact electrodes directly on an OSC surface, due to thermal damage during vacuum evaporation and the effect of solvents during subsequent photolithography. In this work, we demonstrate a simple and facile technique to transfer contact electrodes to ultrathin OSC films and form an ideal metal/OSC interface. Photolithographically defined metal electrodes are transferred and laminated using a polymeric bilayer thin film. One layer is a thick sacrificial polymer film that makes the overall film easier to handle and is water-soluble for dissolution later. The other is a thin buffer film that helps the template adhere to a substrate electrostatically. The present technique does not induce any fatal damage in the substrate OSC layers, which leads to successful fabrication of OTFTs composed of monolayer OSC films with a mobility of higher than 10 cm2 V-1 s-1, a subthreshold swing of less than 100 mV decade-1, and a low contact resistance of 175 Ω⋅cm. The reproducibility of efficient contact fabrication was confirmed by the operation of a 10 × 10 array of monolayer OTFTs. The technique developed here constitutes a key step forward not only for practical OTFT fabrication but also potentially for all existing vertically stacked organic devices, such as light-emitting diodes and solar cells.