|
内容記述 |
Studies on π-electronic molecules have been one of the important subjects in<br />organic electronics and optoelectronics. Introduction of metal modules to conjugated<br />molecules plays an important role in expanding the diversity of supramolecular self-<br />assembly. For example, properties of metal ions such as magnetism, redox, and<br />photochemical activities may be transcribed on the supramolecules. This thesis<br />reports a general strategy for the integration of metal species to π-electronic<br />compounds via conjugation. It demonstrates the first synthesis of conjugated<br />multinuclear metallo complexes and their assemblies to form two-dimensional<br />molecular tapes and sheets with unique electronic and photo functionalities. In<br />relation to these hole-transporting supermolecules, this thesis reports a new kind of n-<br />type conducting molecules with robust thermal stability, high processability, and large<br />electron mobility. These unique properties are unprecedented and highly correlated<br />with their well-defined supramolecular architectures.<br /> Along this line, I reports the development of novel functional macromolecules<br />via topological design, by focusing on the creation of a new class two-dimensional<br />polymers and the finding of light-harvesting effect of conjugated microporous<br />polymers. Exploration of functional macromolecules is one of the interesting and<br />central topics in chemistry, physics, and molecular science. Especially, π-electronic<br />macromolecules are indispensable in molecular devices such as biosensors, light-<br />emitting diodes, and plastic solar cells. Their capabilities of triggering emission,<br />photoinduced energy/electron transfers, and charge carrier transportation are key<br />factors that vitalize device performance. Various 1D conjugated polymers have been<br />developed for these purposes, while the molecular design of 3D conjugated polymers<br />has led to unique dendritic scaffolds for cascade energy transduction. To access 2D<br />polymeric architecture, elaborate modifications of 1D conjugated polymers have led<br /> to findings of 2D anisotropic monolayers and thin films by SAM, LB, and LBL<br /> techniques. Clearly, a covalent 2D polymer assures a robust and shape-persistent<br />polymer network with permanent order in its building blocks. Synthesis of such<br />covalent 2D polymers has been heavily pursed since they are expected to open<br />entirely new vistas for future science and technology. However, the existence of<br /> covalent 2D polymers has not yet been proved and the development of a realistic way<br />to create such polymers remains a major challenge. This thesis describes the first<br /> example of the synthesis of a covalent two-dimensional (2D) conjugated polymer,<br />which is a completely new class of polymer.<br /> As summarized in the above, my thesis consists of the design, synthesis, and<br />functional exploration of supermolecules and macromolecules, with an emphasis on<br />the development of novel π-electronic nanoarchitectures.<br /><br /><b>(1)The Noncovalent Assembly of Benzene-Bridged Metallosalphen Dimer:<br />Photoconductive Tapes with Large Carrier Mobility and Spatially Distinctive<br />Conduction Anisotropy<br /></b> In photoconduction, photo-generated charge carriers move to electrodes and<br/>produce electric current. Studies on such photo-responsive molecules have been an<br />important part of progress in the field of solar energy conversion. Single crystals of<br />certain π-conjugated molecules, <i>e.g.,</i> arenes, have been reported to become<br />photoconductive as a result of exciton migration and charge separation at the<br />molecule-electrode interface. However, small arenes absorb photons only in the<br />ultraviolet region, while large arenes with absorption bands extending to the visible<br />region require complicated synthesis along with tedious purification and are difficult<br />to process. Moreover, the undesirable photoinduced dimerization and bleaching of<br />arenes deter their application to optoelectronics. During a study on the assembly of<br />conjugated multinuclear metallocomplexes, I serendipitously discovered that these π-<br />electronic metallo-conjugates are photo-responsive, robust against irradiation and may<br />avoid the above drawbacks.In the first part, I describes a newly synthesized benzene-<br />bridged metallosalphen dimer tailored with alphatic chains, which is demonstrated for<br />the solution-processed assembly of a π-electronic tape. The tape is unique in that it<br />shows a large intrinsic carrier mobility, is spatially anisotropic in conduction, forms<br /><i>p-</i> or </i>n-</i>type semiconductors tunable upon doping. I emphasizes that the tape is highly<br />responsive to visible light irradiation, triggers prominent photocurrent generation,<br />shows on/off ratios as high as 9.0 × 10<sup>4</sup> and is capable of repeated on-off switching<br />without deterioration. Molecular design of bridged dinuclear metallocomplexes has<br />led to the findings of unusual physical properties and utilities such as catalysts,<br />mimicry for biological enzymes, molecular magnets, building blocks for coordination<br />polymers and MOFs. However, photo functions have been unexplored to date.<br /><br /><b>(2) Noncovalently Netted, Photoconductive Sheets with Extremely High Carrier<br />Mobility and Conduction Anisotropy from Triphenylene-Fused Metal Trigon<br />Conjugates<br /></b> Studies on conjugated molecules have been one of the central subjects in organic<br/>electronics and optoelectronics. Introduction of metal modules to conjugated<br />molecules plays an important role in expanding the diversity of supramolecular self-<br />assembly. For example, properties of metal ions such as magnetism, redox, and<br />photochemical activities may be transcribed on the supramolecules. In this context,<br />triphenylene, a typical conjugated planar molecule, is an intriguing motif for such a<br />purpose due to its utility in supramolecular assembly. However, up to date, metal-<br />containing triphenylene derivatives have been limited to only thio-ligated bismuth and<br />silver crystalline solids. In relation to the first part, here, I reports the first example of<br />triphenylene-fused metal trigon conjugates, where multinuclear metal sites are<br />connected to one another via conjugation with triphenylene core. The metal trigon<br />upon self-assembly forms well-defined 2D sheet, which harvests a wide range of<br />photons, converts them to bright emission, and allows exciton migration. Moreover, <br />the 2D sheet is semiconducting with a high carrier mobility and capable of repetitive<br /> on-off current switching at room temperature. The noncovalent 2D sheet is<br /> photoconductive to exhibit a quick response to visible light irradiation with large<br />on/off ratio. Spatial anisotropy in conductivity reveals that the sheet assembly favors a<br />conduction path perpendicular to the stacked sheets other than the one along the sheet<br />planes. These characters are unique and clearly originate from the highly ordered<br />molecular structure of the noncovalent sheet assembly.<br /><br /><b>(3）Pyrene-Fused Phenazine Bisimides as Robust, Solution Processable and<br />Chemically Addressable n-Channel Organic Semiconductors<br /></b> Organic semiconductors have attracted great interests in relation to their utilities<br />in optoelectronics and molecular electronics. In contrast to rich varieties of <i>p-</i>type<br />semiconductor, <i>n-</i>type organic semiconductor has been very limited in numbers to<br />certain electron-withdrawing π-conjugation systems including perfluorinated aromatic<br />compounds, heteroaromatic compounds, and fullerene derivatives. Due to electronic<br />deficient nature, n-type organic semiconductors are usually unstable and air sensitive<br />in conducting condition. Recently, bisimides with aromatic cores such as anthracene,<br />naphthalene, perylene, and tetrathiafulvalene moieties have been reported to function<br />as n-type semiconductor, which allows supramolecular self-assembly upon tailoring<br />at bisimide terminals with alkyl chains to fabricate various nanostructured devices.<br />Very recently, phenazine compounds have been demonstrated to be <i>n-</i>type<br />semiconductor with high carrier mobility due to the presence of electron-withdrawing<br />imine units. In this part, I report a molecular system combining three structural<br />parameters (1) bisimide terminals, (2) phenazine linkages, and (3) an extended π-<br />conjugation pyrene core, <i>i.e.,</i> pyrene-fused phenazine bisimide as a novel <i>n-</i>type<br />organic semiconductor. I highlights that such a topological design allows a multiple<br />combination of high thermal and air stability, ordered crystalline packing together<br />with facile solution processability. Moreover, protonation of phenazine units leads to<br />the generation of quadruple cationic bisimide, thus converting the conjugated neutral<br />skeleton to positively charged backbone. We found that bisimide and cationic<br />bisimide are n-type semiconducting with the largest charge carrier mobility of 4.1<br />cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup> and capable of stable repetitive on/off current switching in ambient<br />condition.<br /><br /><b>(4) Synthesis of Covalent Two-Dimensional Polymers Using a Topological Approach</b><br /> Conjugated polymers are commonly used for a wide variety of applications.<br />Extensive research has led to the realization of one-dimensional linear and three-<br />dimensional hyperbranched and dendritic conjugated polymers. Despite tremendous<br />efforts, a fully-characterized covalent two-dimensional conjugated polymer has not<br />yet been achieved and its creation remains a substantial challenge. In this part I<br />reports the synthesis of a two-dimensional conjugated poly(para-phenylene), by<br />covalently 'knitting' one-dimensional linear conjugated chains, based on a specific<br />topological two-dimensional cross-coupling polycondensation reaction. This 2D<br />polymer is crystalline and consists of flat square sheets with very clear and smooth<br />edges. It holds extremely dense interwoven longitudinal and latitudinal straight chains<br />of 6.6 × 10<sup>6</sup> cubic micrometer and possesses persistent, long-range, periodic<br />repeating-unit order. Electronic experiments and transient conductivity measurements<br />predict that two-dimensional conjugated polymers would exhibit completely novel<br />properties when used in molecular electronics and optoelectronics.<br /><br /><b>(5) Light-Harvesting Conjugated Microporous Polymers: Spatial Confinement<br />and Inner Surface-Interfered Energy Transduction</b><br /> Conjugated microporous polymers (CMPs) are amorphous polymers with<br />conjugated framework and inherent three-dimensional porous structure. Owing to their<br />unique pore sizes which could be tuned through molecular design, CMPs serve<br />as a bridge between zeolites and MOFs/COFs. However, most studies to date have <br />mainly focused on the gas storage and separation properties. I envisioned that the<br />highly dense π-electronic components of CMPs framework could serve as antennae<br />for collecting photons, while the well-defined inner pores could embed and spatially<br />confine energy-accepting counterparts, thus leading to the fabrication of a<br />supramolecular system for energy transduction mediated by the large inner surface of<br />CMPs. In the last part of this thesis, the author reports the first example of light-<br />harvesting CMPs, which consist of microporous polyphenylene framework as<br />antennae and coumarin 6 noncovalently encapsulated within the pore as energy-<br />accepting pool. The CMP-based light-harvesting system not only allows the creation<br />of a novel noncovalent energy donor-acceptor array but much importantly makes it<br />possible a directional pinpoint energy transfer from the framework to the energy<br />converter. These characters together with a large inner surface facilitate the energy<br />transduction process and result in an almost 100% energy transfer quantum eficiency.<br />These unique properties constitue an important step to the utility of CMPs in sensing<br />and optoelectronics.<br /> Exploration of functional supramolecular and macromolecular nanoarchitectures<br />is a subject that has a high probability to lead to the development of new materials. In<br />summary, the author has developed a series of novel π-electronic supermolecules and<br />macromolecules. The author designed and synthesized a series of new π-electronic<br />multinuclear metallo conjugates and n-type conjugated molecules and succeeded in<br />the construction of π-electronic two-dimensional assemblies. By using topological<br />molecular design, a new class of polymers, i.e., covalent two-dimensional polymer<br />was created. By exploration of the porous channel, a novel light-harvesting antenna<br />based on conjugated microporous polymers was established. These π-electronic<br />organic architectures show unique photo and electrical functions that clearly originate<br />from their highly ordered structures and thus open a new way to molecular<br />optoelectronics and electronics. |
要旨・審査要旨 (663.7 kB)
