高エネルギー荷電粒子による固相重合反応と機能性ナノ材料の創製に関する研究

京都大学新制・課程博士博士(工学)甲第24585号工博第5091号新制||工||1975(附属図書館)京都大学大学院工学研究科分子工学専攻(主査)教授 関 修平, 教授 梶 弘典, 教授 SIVANIAH Easan学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

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

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

Conjugated Nanowire Sensors via High-Energy Single-Particle-Induced Linear Polymerization of 9,9\u27-Spirobi[9H‑fluorene] Derivatives

Nanostructures composed of conjugated polymers or π-conjugated molecules provide sensing platforms with large specific surface areas. One of the feasible approaches to accessing such nanostructured miniaturized sensors with ultrahigh sensitivity is to develop a network of organic nanowires with optical/electronic properties that can measure signals upon interacting with the analytes at their surfaces. In this work, organic nanowires with controlled number density and uniform length were fabricated by one-dimensional solid-state polymerization of 9,9\u27-spirobi[9H-fluorene] (SBF) derivatives triggered by high-energy single particles. SBF was chosen as a conjugated molecular motif with the interplay of high density of π-electrons, high solubility, and uniform solid-state structures, allowing us to fabricate sensing platforms via solution processing. The as-deposited energy density in linear polymerization nanospace was theoretically analyzed by a collision model, interpreting nanowire sizes at subnanometer levels. The substitution of bromine atoms was confirmed to be effective not only for the higher collision probability of the incident particles but also for the remarkable increase in radiolytic neutral radical yield via C−Br cleavages or electron-dissociative attachments onto the bromine atoms. The fluorescence spectra of SBF-based nanowires were different from those of SBF derivatives due to extended bond formation as a result of polymerization reactions. Fluorescence was quenched by the addition of nitrobenzene, indicating the potential use of our nanowires for fluorometric sensing applications. Microwave-based conductivity measurements revealed that the SBF-based nanowires exhibited charge carrier transport property upon photoexcitation, and that the conductivity was changed upon treatment with nitrobenzene vapors. The presented strategy of bromination of aromatic rings for efficient fabrication of controlled nanowire networks with favorable fluorescent and charge transport properties of nanowires advances the development of nanostructured sensing systems

Donor/Acceptor Segregated π‑Stacking Arrays by Use of Shish-Kebab-Type Polymeric Backbones: Highly Conductive Discotic Blends of Phthalocyaninatopolysiloxanes and Perylenediimides

Construction of large-area electron donor–acceptor (D–A) interfaces and hole/electron pathways is important for photoconducting and photovoltaic functions. Although blends of D- and A-type discotic π-systems have a possibility to realize one-dimensional charge carrier pathways as well as heterointerfaces, D–A segregated structures are difficult to develop by self-assembly because they are entropically unfavored structures. Here we report the use of shish-kebab-type hole-transporting discotic columns fixed by a self-threading polysiloxane chain and approach to such segregated nanostructures. Electron-donor/acceptor blends of soluble phthalocyaninato­polysiloxanes (Poly-SiPcs) and perylenedicarboximides (PDIs) were prepared, and their photoconductive property was investigated. Although <b>Poly-SiPc1</b> shows a photoinduced charge separation with <b>PDI1</b> analogous to the corresponding monomeric phthalocyanines (<b>SiPc1</b> and <b>H</b>_<b>2</b><b>Pc1</b>), the <b>Poly-SiPc1</b>/<b>PDI1</b> system displays a remarkably larger photoconductivity than <b>SiPc1/PDI1</b> and <b>H</b>_<b>2</b><b>Pc1</b>/<b>PDI1</b>, which mostly results from the presence of hole-transporting pathways with the mobility μ_h,1D ∼ 0.1 cm² V^–1 s^–1 in <b>Poly-SiPc1</b> along the polysiloxane covalent bonds even upon mixing with <b>PDI1</b>. When π-stackable <b>PDI2</b> is used instead of <b>PDI1</b>, X-ray diffraction analysis disclosed obvious signs of π-stacking periodicities for both Pc and PDI planes in the mixture, indicating the presence of donor–acceptor segregated domains of columnar structures. As a result, photoexcitation of <b>Poly-SiPc1</b>/<b>PDI2</b> generates highly mobile holes and electrons, leading to the observation of a much larger conductivity

Porphyrin Nanowire Bundles for Efficient Photoconductivity, Photoemission, and Generation of Singlet Oxygens toward Photodynamic Therapy

Energy released from an accelerated high-energy single/cluster particle triggers solid-state polymerization and cross-linking reactions of porphyrin-based π-conjugated monomers within a nanometer-scaled one-dimensional spatial area along the ion trajectory, resulting in the formation of an insoluble nanowire with a precise diameter and length. The nanowires are isolated by the development process—immersion of the irradiated film in organic solvents—and their shape and geometry are clearly characterized by atomic force microscopy. The obtained nanowire bundles, reflecting precisely the number of incident particles, show characteristic absorption spectra originating from porphyrin chromophores without significant degradation of the molecular cores. These porphyrin-based nanowires can be further functionalized into metallocomplexes by immersing the nanowires into solutions containing metal ion sources. The remarkable finding on the monomer structural parameters is that terminal alkyne groups are preferentially reacted and thus highly effective as a monomer structure for the present single particle-triggered linear polymerization method. The porphyrin-based nanowires show much higher photoconductivity than the precursor porphyrin films and enhanced fluorescence on silver nanoparticle layers via surface plasmon resonance. The porphyrin nanowires serve as photosensitizers mediating the generation of singlet oxygens, which is attractive for the use as a controlled nanosystem toward photocatalysis and photodynamic therapy

Ubiquitous Organic Molecule-based Free-standing Nanowires with Ultra-high Aspect Ratios

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 this decade. 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 device integration; however, the steep increase in the number of surfaces and their interaction in 3D nanospace make it hard to integrate nanostructures with aspect ratios over ~10. We report herein a unique technique to produce uniform free-standing 1D nanostructures with extremely high aspect ratios over 100, borrowing from technology developed for cancer radiotherapy with high-energy charged particles. Along the straight trajectory of particles penetrating the condensed phase of a variety of sublimable organic molecules, 1D nanowires were formed with single-nm thickness and perfectly controlled length. An all-dry process was developed to isolate the nanowire plexus, and hetero-junction structures could be facilely built into the nanowires by the new technique. Coaxial extension of nanowires by a chemical process allowed us to freely design the nanowires both in axial and radial directions

Observation of a Critical Charge Mode in a Strange Metal

Quantum electronic matter has long been understood in terms of two limiting behaviors of electrons: one of delocalized metallic states, and the other of localized magnetic states. Understanding the strange metallic behavior which develops at the brink of localization demands new probes of the underlying electronic charge dynamics. Using a state-of-the-art technique, synchrotron-radiation-based Mossbauer spectroscopy, we have studied the longitudinal charge fluctuations of the strange metal phase of beta-YbAlB4 as a function of temperature and pressure. We find that the usual single absorption peak in the Fermi-liquid regime splits into two peaks upon entering the critical regime. This spectrum is naturally interpreted as a single nuclear transition, modulated by nearby electronic valence fluctuations whose long time-scales are further enhanced, due to the formation of charged polarons. Our results represent a direct observation of critical charge fluctuations as a new signature of strange metals

ANGPTL2 activity in cardiac pathologies accelerates heart failure by perturbing cardiac function and energy metabolism

A cardioprotective response that alters ventricular contractility or promotes cardiomyocyte enlargement occurs with increased workload in conditions such as hypertension. When that response is excessive, pathological cardiac remodelling occurs, which can progress to heart failure, a leading cause of death worldwide. Mechanisms underlying this response are not fully understood. Here, we report that expression of angiopoietin-like protein 2 (ANGPTL2) increases in pathologically-remodeled hearts of mice and humans, while decreased cardiac ANGPTL2 expression occurs in physiological cardiac remodelling induced by endurance training in mice. Mice overexpressing ANGPTL2 in heart show cardiac dysfunction caused by both inactivation of AKT and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a signalling and decreased myocardial energy metabolism. Conversely, Angptl2 knockout mice exhibit increased left ventricular contractility and upregulated AKT-SERCA2a signalling and energy metabolism. Finally, ANGPTL2-knockdown in mice subjected to pressure overload ameliorates cardiac dysfunction. Overall, these studies suggest that therapeutic ANGPTL2 suppression could antagonize development of heart failure