Toshihiro Okamoto

The University of Tokyo | Todai · Department of Advanced Materials Science

We report a facile synthetic protocol for preparation of dinaphtho[2,3-b:2',3'-d]furan () derivatives. derivatives showed high emissive behaviour in solid. A solution-crystallized transistor based on alkylated derivatives showed an excellent carrier mobility of up to 1.3 cm(2) V(-1) s(-1), thereby proving to be a new solution-processable active org...

V-shaped organic semiconductors are designed and synthesized via a large-scale applicable synthetic route. On page 6392, Jun Takeya, Toshihiro Okamoto and co-workers describe solution-crystallized films based on such molecules and demonstrate that they have high-performance transistor properties with maximum mobilities of up to 9.5 cm(2) V(-1) s(-1...

We report a novel solution-crystallization method to grow two-dimensional platelet-shaped single-crystals of well-known insoluble organic semiconductors via thermal conversion of their precursor molecules dissolved in ionic liquids (ILs). By optimizing conditions of the crystal growth regarding physical properties of ILs such as density and viscosi...

V-shaped organic semiconductors have been designed and synthesized via a large-scale applicable synthetic route. Solution-crystallized films based on such molecules have demonstrated high-performance transistor properties with maximum mobilities of up to 9.5 cm(2) V(-1) s(-1) as well as pronounced thermal durability of up to 150 °C inherent in the...

Molecular doping: The standard model for molecular p-doping of organic semiconductors (OSCs) assumes integer charge transfer between OSC and dopant. This is in contrast to an alternative model based on intermolecular complex formation instead. By systematically varying the acceptor strength it was possible to discriminate the two models. The latter...

Organic semiconductors (OSCs) with π-electron skeletons (π-cores) have garnered significant attention. The development of innovative molecules with high carrier mobility necessitates strategic molecular design. One critical property affecting the carrier mobility of π-conjugated OSCs is the molecular arrangement, particularly the two-dimensional (2...

We present the herringbone structure search (HSS) method to predict the crystal structures of organic semiconductors from molecular structural formulas. The charge transport efficiency of small-molecule organic semiconductors is governed by molecular packing, often in a two-dimensional herringbone structure. This method predicts crystal structures...

[8]Thienophenacene analogues offer excellent single-crystal platforms for hole transport owing to their characteristic molecular orbitals and sufficiently small effective masses.

The crystal structure of organic semiconductors is an important factor that dominates various electronic properties, including charge transport properties. However, compared with the crystal structures of inorganic semiconductors, those of organic semiconductors are difficult to determine by powder x-ray diffraction (PXRD) analysis. Our proposed ma...

Owing to the growing global increase in electronic and electrical waste (e‐waste), significant challenges arise regarding the proper disposal of electronic devices. One potential solution that has gained attention is the development of disposable electronics, in which all components are designed to be for safe and environmentally friendly disposal....

This paper reports that specific attractive intermolecular interactions between side-chain substituents can be useful for enhancing charge-carrier mobility in organic semiconductors owing to the suppression of molecular motions.

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 lim...

Organic semiconductors with distinct molecular properties and large carrier mobilities are constantly developed in attempt to produce highly‐efficient electronic materials. Recently, designer molecules with unique structural modifications have been expressly developed to suppress molecular motions in the solid state that arise from low‐energy phono...

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...

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...

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 o...

Organic thin-film transistors (OTFTs) are promising building blocks for low cost, low-environmental load, and lightweight electronic devices. Carbon-based conductors can be potentially used as TFT electrodes. However, a concern is that the carbon electrode is unsuitable for carrier injection into organic semiconductors due to the difficulty in prec...

Organic thin-film transistors (OTFTs) are promising building blocks of flexible printable electronic devices. Similar to inorganic FETs, OTFTs are heterostructures consisting of metals, insulators, and semiconductors, in which nanoscale interfaces between different components should be precisely engineered. However, OTFTs use noble metals, such as...

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 o...

Molecular design strategy of the π‐electron core is of importance to enhance the organic semiconducting performance. In this study, diphenanthro[1,2‐b:2′,1′‐d]thiophene (DPT) as a new zigzag‐shaped sulfur‐bridged π‐electron core and its phenyl‐substituted derivative (Ph–DPT) exhibiting unique orbital configurations are reported. The DPT derivatives...

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 concep...

Functionalization of π-conjugated compounds is an important strategy to tune electronic states and aggregated structures, leading to development of high-performance organic optoelectronic materials ranging from small molecules to conjugated polymers. Regioselective functionalization can be particularly striking for highly ordered aggregated structu...

Organic 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 clas...

To clarify the limiting factor of carrier transport in organic molecular semiconductors, we performed charge modulation spectroscopy of a field-effect transistor with a 3,11-didecyldinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (C10-DNBDT-NW) single crystal, which showed a hole-carrier mobility of 8.4 cm² V⁻¹ s⁻¹ at 295 K. The terahertz ab...

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 cha...

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...

A highly conductive metallic gas that is quantum mechanically confined at a solid-state interface is an ideal platform to explore non-trivial electronic states that are otherwise inaccessible in bulk materials. Although two-dimensional electron gases have been realized in conventional semiconductor interfaces, examples of two-dimensional hole gases...

A desymmetrization strategy has been devised in the design of molecular cylinders to maximize the dissymmetry factor relevant to circularly polarized light. Although the highest dissymmetry factor of organic molecules was previously achieved with a chiral belt‐persistent cycloarylene having magnetic and electric transition dipole moments in paralle...

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 l...

Desymmetrization of chiral cylindrical cycloarylenes ought to be beneficial to maximize the dissymmetry factor g via reduction of the electric dipole moment μ. An ideal D2 molecule has been synthesized by cross-coupling macrocyclization of two different arylene panels. Twists in biaryl linkages, however, enlarged an orthogonal component of μ, and t...

Self-organization in π-conjugated polymers gives rise to a highly ordered lamellar structure, in which inter-chain stacking spontaneously forms two-dimensional conjugated sheets. This multi-layer stacked nature of semicrystalline polymers allows the inclusion of various functional molecules. In particular, redox-triggered ion-intercalation is an id...

Thin‐film devices are typically fabricated through a bottom‐up approach, wherein the constituents are deposited sequentially from the bottom to top layer. This method requires the precise management of the heterointerfaces, which leads to complicated integration issues particularly in solution‐processed organic thin‐film transistors (OTFTs). This l...

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 an...

Molecular assembly is a crucial factor for charge transports in organic semiconductors (OSCs), and molecularly flexible alkyl chain substitution is a key design feature for achieving desired molecular assemblies. However, the high degree of freedom of alkyl chains leads to molecular fluctuations that are detrimental to OSC performances. Stabilizati...

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...

In organic molecular semiconductors (OSCs), fluctuation of transfer integrals originating from thermally induced molecular vibrations is suggested to cause large scatterings of carriers, and to be a most important factor for the suppression of their carrier mobility. The intrinsic carrier mobility under such a fluctuation of transfer integrals is c...

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 tech...

Variation of aggregated structures driven by side chains is a crucial issue in organic semiconductors (OSCs) for achieving high carrier mobility and device durability. In this work, phenylalkyl side chains composed of a rigid terminal phenyl group and a flexible alkyl linker were studied based on a state-of-the-art n-type ?-electron system, 3,4,9,1...

A highly conductive metallic gas that is quantum mechanically confined at a solid-state interface is an ideal platform to explore nontrivial electronic states that are otherwise inaccessible in bulk materials. Although two-dimensional electron gas (2DEG) has been realized in conventional semiconductor interfaces, examples of two-dimensional hole ga...

Self-organization in π-conjugated polymers gives rise to a highly ordered lamellar structure, in which inter-chain stacking spontaneously forms two-dimensional conjugated sheets. This multi-layer stacked nature of semicrystalline polymers results not only in effective charge transport, but also allows the inclusion of various functional molecules a...

Towards the development of high-performance small molecule-based organic semiconductors with high carrier mobility and high thermal durability, strategic and systematic investigations are needed for not only molecular design of π-electron cores and substituents but also fundamental and structural analyses. Here, we focus on the sulphur-containing V...

Benzo[ de ]isoquinolino[1,8- gh ]quinolinetetracarboxylic diimide (BQQDI) n-type organic semiconductors demonstrate unique multi-fold intermolecular hydrogen-bonding interactions that lead to excellent aggregated structures, charge transports, and electron mobility. However, the robust intermolecular anchoring of BQQDI presents challenges for furth...

Transistors, the most important logic elements, are maintained under dynamic influence during circuit operations. Practically, circuit design protocols and frequency responsibility should stem from a perfect agreement between the static and dynamic properties. However, despite remarkable improvements in mobility for organic semiconductors, the corr...

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,...

Deposition of metallic electrodes on a semiconductor medium is an indispensable factor in governing carrier injection, and a metal/semiconductor contact that can be formed via solution process is highly desired in printed electronics. However, fine‐patterning the solution processes of metallic electrodes without damaging the excellent electronic pr...

Bent-shaped p-type organic semiconductors (OSCs) have demonstrated high hole-carrier mobilities and thermal durability for practical electronic applications, among which, the V-shaped thieno[3,2-f:4,5-f’]bis[1]benzothiophene (TBBT–V) π-electron core shows excellent electronic features for hole transports, and the fused terminal thiophene units allo...

Organic field-effect transistors (OFETs) have attracted great attention as key elements in Internet-of-Thing (IoT) devices due to their advantages of low cost and mass producibility made possible by printing technology. Such devices require organic semiconductors (OSCs) that intrinsically possess high carrier mobility and air stability. In addition...

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 pre...

Significant progress has been made in both molecular design and fundamental scientific understanding of organic semiconductors (OSCs) in recent years. Suitable charge-carrier mobilities (µ) have been obtained by many high-performance OSCs (µ > 10 cm2 V 1 s 1), but drawbacks remain, including low solution processability and poor thermal durability....

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...

Prediction of material properties of newly designed molecules is a long-term goal in organic electronics. In general, it is a difficult problem, because the material properties are dominated by the unknown packing structure. We present a practical method to obtain charge transport properties of organic single crystals, without use of experimental s...

Although high carrier mobility organic field‐effect transistors (OFETs) are required for high‐speed device applications, improving the carrier mobility alone does not lead to high‐speed operation. Because the cut‐off frequency is determined predominantly by the total resistance and parasitic capacitance of a transistor, it is necessary to miniaturi...

Arranging molecules into highly symmetric, topological crystal structures has been recognized as the best approach to functionalize electronic properties in molecular crystals, where the constituent molecules have been assumed to be rigid in shape. Here, in striking contrast, we demonstrate that the molecules in a monolayer organic crystal can unde...

Significance Organic thin film transistors (OTFTs) are promising building blocks in next-generation electronic devices due to the compatibility with the solution process of organic semiconductors (OSCs). Generally, OTFT processes inevitably face the serious issue that the available substrates are limited to those that are solution-process compatibl...

Building on significant developments in materials science and printing technologies, organic semiconductors (OSCs) promise an ideal platform for the production of printed electronic circuits. However, whether their unique solution-processing capability can facilitate the reliable mass manufacture of integrated circuits with reasonable areal coverag...

In microcrystal samples of the prototypical organic molecular semiconductors rubrene and C10-DNTT (2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene), we measured spectra of complex optical conductivity caused by photocarriers with optical-pump terahertz-probe spectroscopy. We analyzed the σ̃ω spectra using the Drude-Smith model and evalua...

The efficiency with which polymeric semiconductors can be chemically doped—and the charge carrier densities that can thereby be achieved—is determined primarily by the electrochemical redox potential between the π-conjugated polymer and the dopant species1,2. Thus, matching the electron affinity of one with the ionization potential of the other can...

In this paper, the molecular design of the first deep-lowest unoccupied molecular orbital (LUMO) level diimide π-electron core, benzo[c]thiophene diimide (BTDI), as a novel n-type organic semiconductor was determined. An original synthetic sequence was devised to obtain the target cyclohexyl-BTDI (Cy6-BTDI) derivative. Cy6-BTDI demonstrated complet...

The development of organic semiconductors (OSCs) applicable to organic field-effect transistors is crucial to printed and flexible electronics. OSCs must meet several prerequisites: 1) high chemical stability, 2) charge carrier mobility exceeding 10 cm2/Vs, 3) appropriate solubility, and 4) high thermal durability. The author and collaborators deve...

Bis[1]benzothieno[5,4-d:5′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (BBTBDT-2) and its phenyl-substituted derivative were successfully synthesized and characterized. From DFT calculations, highest occupied molecular orbitals (HOMOs) of both compounds are well delocalized and large orbital coefficients exist on sulfur atoms. Single-crystal X-ray analysi...

Terahertz Raman spectroscopy was performed on high-mobility organic single-crystal semiconductors, by which the phonon energy at the Gamma point was qualified as a function of external uniaxial strain. The observation of peak shifts in Raman modes under uniaxial strain revealed that application of an external strain can effectively tune the intermo...

Organic semiconductors are of scientific and technological interest due to their potential in printable and flexible electronic applications such as organic field‐effect transistors (OFETs), organic light‐emitting diodes (OLEDs), and organic photovoltaic cells (OPVs). The functions of organic semiconductors are generated by intermolecular charge tr...