Cyclobuteno[60]fullerenes as efficient n-type organic semiconductors

Cyclobuteno[3,4:1,2][60]fullerenes have been prepared in a straightforward manner by a simple reaction between [60]fullerene and readily available allenoates or alkynoates as organic reagents under basic and mild conditions. The chemical structure of the new modified fullerenes has been determined by standard spectroscopic techniques and confirmed by X-Ray diffraction analysis. Some of these new fullerene derivatives exhibit a remarkable intrinsic electron mobility – determined by using flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements – which surpasses that of the well-known PCBM, thus behavi ng as promising n-type organic semiconductors

Repeat protein scaffolds: ordering photo- and electroactive molecules in solution and solid state

The precise control over the organization of photoactive components at the nanoscale is one of the main challenges for the generation of new and sophisticated macroscopically ordered materials with enhanced properties. In this work we present a novel bioinspired approach using protein-based building blocks for the arrangement of photo and electroactive porphyrin derivatives. We used a designed repeat protein scaffold with demonstrated unique features that allow for the control of their structure, functionality, and assembly. Our designed domains act as exact biomolecular templates to organize porphyrin molecules at the required distance. The hybrid conjugates retain the structure and assembly properties of the protein scaffold and display the spectroscopic features of orderly aggregated porphyrins along the protein structure. Finally,we achieved a solid ordered bio-organic hybrid thin film with anisotropic photoconductivity

Ubiquitous organic molecule-based free-standing nanowires with ultra-high aspect ratios

ごくありふれた有機分子からナノ細線をつくり立たせて埋めつくす --立体電子回路や超高感度センサーへ--. 京都大学プレスリリース. 2021-06-30.The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems

Protein-directed crystalline 2D fullerene assemblies

Water soluble 2D crystalline monolayers of fullerenes grow on planar assemblies of engineered consensus tetratricopeptide repeat proteins. Designed fullerene-coordinating tyrosine clamps on the protein introduce specific fullerene binding sites, which facilitate fullerene nucleation. Through reciprocal interactions between the components, the hybrid material assembles into two-dimensional 2 nm thick structures with crystalline order, that conduct photo-generated charges. Thus, the protein-fullerene hybrid material is a demonstration of the developments toward functional materials with protein-based precision control of functional elements

Unraveling unprecedented charge carrier mobility through structure property relationship of four isomers of didodecyl[1]benzothieno[3,2-b][1]benzothiophene

Since the dawn of organic electronics in the 1970’s, academic and industrial research efforts have led to dramatic improvements of the solubility, stability, and electronic properties of organic semiconductors (OSCs).[1, 2] The common benchmark to characterize the electrical performances of OSCs is their charge carrier mobility μ (cm2 V–1 s–1), defined as the drift velocity of the charge carrier (cm s–1) per unit of applied electric field (V cm–1). Reaching high mobilities in OSCs is highly desirable as it allows faster operation of transistors and energy savings by reduced calculation times.[2, 3] However, OSCs performances (conventional values usually range from 1 to 10 cm2 V–1 s–1, with highest values obtained with single-crystal devices mostly exempt of structural defects) are still not comparable to that of state-of-the-art inorganic semiconductors (e.g. metal oxides with µ = 20-50 cm2 V–1 s–1 and polycrystalline silicon with µ > 100 cm2 V–1 s–1) thereby hampering important potential technological applications such as flexible organic light-emitting diode (OLED) displays and wearable electronics.[3, 4

<論文・報告>Development of Low-temperature Microwave-based Measurement Systems Evaluating Local-scale Charge Carrier Mobility at Interfaces

本研究論文は，ELCAS 専修コース物性物理化学分野の研究成果をまとめたもので，この一部の成果を含む内容が，ACS Omega 誌（2017, 2, 164?170, http://pubs.acs.org/doi/abs/10.1021/acsomega.6b00428）に2017年1月20日付で掲載された．原著は英文のみで，閲覧は誰でも可能（オープンアクセス）である．Charge carrier mobility is one of the most important physical properties for evaluating semiconductor performance. In this study, we employed field-induced time-resolved microwave conductivity (FITRMC) method featuring contactless evaluation of intrinsic carrier mobility, instead of the widely used field-effect transistor (FET) approach. In order to analyze the electronic properties of the semiconducting materials, temperature control is a significant subject. In this study, we have addressed to develop the variable-temperature (VT) FITRMC system. Graphene and pentacene were selected as target materials and each of them was evaluated at ?70~22°C using the FI-TRMC method under the flow of cooled N2 gas. The single-layer graphene and vapor-deposited pentacene on a poly(methylmethacrylate) layer showed negative and positive correlations between temperature and hole mobility, respectively. This observation strongly agrees with the proposed conduction mechanisms; i.e., the band model was most likely operated for the single-layer graphene while the hopping conduction dominated the pentacene. From the Arrhenius plots, the activation energy of pentacene was estimated at 92 meV, which agrees with that previously reported for typical organic semiconductors. These results indicate the reliability of our VT FI-TRMC system. 半導体性能を評価する重要な指標として，電荷移動度が挙げられる．これを測定する従来のField Effect Transistor（FET）法に対し，本研究では絶縁体- 対象材料界面での局所的な電荷輸送特性の選択的評価が可能なField-Induced Time-ResolvedMicrowaveConductivity（FITRMC）法を用いた．材料の電子物性を調べるにあたり，温度の制御は新たな知見を得るのに重要な要素である．そこで今回は，材料にグラフェンとペンタセンを使用し，?70℃~室温においてそれぞれの電荷輸送機構を解析することで，温度可変FI-TRMC法の確立を目指した．電荷輸送機構は，グラフェンはバンド伝導，ペンタセンはホッピング伝導であることが知られている．測定装置の空洞共振器付近を断熱材で覆い，その中を液体窒素で冷やした窒素ガスをフローさせるシステムを今回新たに構築し，試料の移動度の温度依存性を調べたところ，グラフェン素子では温度上昇に伴い正孔移動度の減少が確認され，ペンタセンではその逆の傾向を示すことから，それぞれ提唱されているバンドおよびホッピング伝導機構を支持した．ペンタセンに関しては，実験データから92 meV という活性化エネルギー値を算出し，既報の有機半導体の値に近いことを確認した．これらの結果は，本研究で開拓した温度可変FI-TRMC 法が低温実験法として信頼できることを支持している

Highly Efficient Solid-State Intra-Track Polymerization of Ethynyl-Substituted Spirobifluorenes Triggered by Swift Heavy Ion Irradiations

Acetylenes are the first monomer to polymerize by the energy deposited by ionizing radiations. Herein we report an extremely efficient solid state polymerization of ethynyl-substituted 9,9\u27-spirobi[9H-fluorene]s (SBFs) via a unique nano-fabrication technique referred to as Single Particle Trigged Linear Polymerization (STLiP) initiated by high energy charged particles. The resulted nanowires of polymerized/crosslinked SBFs show a gradual transformation from flexible to rigid rod-like with an increase in the reaction efficiency mediated by the ethynyl substitution. The overall efficiency of initiation/propagation/crosslinking reactions is remarkably high even in comparison with the primary yield of ionization events in the radiation chemical processes, marking up to G > 80 (100 eV)^-1, which is suggestive of efficient chain reactions in the propagation steps. The present results demonstrate efficient solid-state polymerization reactions, which are neither topochemical polymerization reactions nor acid/base catalyzed reactions, expand the versatility of STLiP technique to fabricate 1D nanomaterials based on a variety of organic compounds

Assembled Structures of Anion-Responsive π‑Systems Tunable by Alkyl/Perfluoroalkyl Segments in Peripheral Side Chains

Anion-responsive π-conjugated molecules carrying semifluoroalkyl chains were newly synthesized to examine the self-assembling features and resulting electronic properties of these molecules and of ion-pairing complexes formed when combined with a planar cation salt. Although these compounds self-organize into columnar mesophases similar to that of their hydrocarbon analog, in both the charge-free and charge-based states, the fluorous moieties appended to the π-conjugated units change the detailed phase-transition profiles and improve the thermal stability of the ion-pairing complexes. The length of the fluoroalkyl chains at the termini strongly affects the charge carrier mobility through the one-dimensionally arranged π-conjugated motifs, giving highly mobile charge carriers with extremely high intrinsic mobility of 1.1 cm² V^–1 s^–1 as a maximum value