京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19740号 / 工博第4195号 / 新制||工||1647(附属図書館) / 32776 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 阿部 竜, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21789号 / 工博第4606号 / 新制||工||1717(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 田中 庸裕, 教授 佐藤 啓文, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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This dissertation research work focuses on the investigation of novel donor-acceptor systems elucidating their photochemical properties, anion binding, and their potential application in the development of artificial photosynthetic systems. The explored systems are based on oxoporphyrinogen (OxPs), porphyrins, fullerene, and boron dipyrromethene (BODIPY) based donor-acceptor systems. The photochemical properties of novel molecular systems were elucidated using UV-vis spectroscopy, fluorescence spectroscopy, electrochemical methods, computational calculations, and ultrafast transient absorption spectroscopy. A novel BODIPY-oxoporphyrinogen dyad which is able to bind with fluoride anion promoting the excited state ultrafast electron and energy transfer events mimicking the primary events in natural photosynthesis was introduced. Further, self-assembly of supramolecular complexes based on oxoporphyrinogens, fullerene, and different zinc porphyrin dimers was explored. The formed self-assembled complexes have shown photoinduced electron transfer. A novel push-pull supramolecular construct based on the spiro-locked N-heterocycle-fused zinc porphyrin was studied. The excited state charge separation and stabilization of this push-pull system was enhanced by the complexation with fluoride anion. Also, the effect of BODIPY functionalization and linkers on the electron transfer properties of a series of carbazole–BODIPY and phenothiazine-BODIPY dyads were investigated. These findings are important to develop advanced and efficient BODIPY-based donor-acceptor systems for efficient light harvesting applications. The entire study aims to expand our understanding of these systems and contribute towards the advancement of sustainable energy technologies.

Biomimetic catalysis is an important research field, as a better understanding of nature´s powerful toolbox for the conversion of molecules can lead to technological progress. [FeFe]-hydrogenases are very efficient catalysts for hydrogen production. These enzymes play a crucial role in the metabolism of green algae and certain cyanobacteria. Their active site consists of a diiron complex that is embedded in an interactive protein matrix. In this thesis, two pathways for mimicking the outer coordination sphere effects resulting from the protein matrix are explored. The first is the construction of model complexes containing phosphine ligands that are coordinated to the iron center as well as covalently linked to the bridging ligand of the complex. The effect of such linkers is an increased energy barrier for the rotation of the Fe(CO2)(PL3)-subunit, which potentially could stabilize a terminal hydride that is an important intermediate in the proton reduction cycle. The second pathway follows the incorporation of [FeFe]-hydrogenase active site model complexes into metal-organic frameworks (MOFs). Resulting MOF-catalysts exhibit increased photocatalytic activity compared to homogenous references due to a stabilizing effect on catalytic intermediates by the surrounding framework. Catalyst accessibility within the MOF and the influence of the framework on chemical reactivity are examined in the work presented. Furthermore, an initial step towards application of MOF-catalysts in a device was made by interfacing them with electrodes. The work of this thesis highlights strategies for the improvement of biomimetic model catalysts and the knowledge gained can be transferred to other systems mimicking the function of enzymes.

Doctor of Philosophy / Department of Chemistry / Stefan Bossmann / Tris-homoleptic ruthenium(II)-quaterpyridyl and quaterpyridinium complexes, with +8 and +14 charge were synthesized by utilizing high pressure reaction pathway. These complexes have diameters ranging from 1.82 to 4.55 nm according to the molecular modeling calculations. These ruthenium complexes are highly luminescent and contain long excited state life times. The novel ruthenium(II)-quaterpyridinium complexes exhibit superior reactivity as sensitizer-relay-assemblies (SRA‟s) in sacrificial systems for water and carbon dioxide reductions, while harvesting the ultraviolet- and most of the visible fraction of the incident solar spectrum. Ru(II)-quaterpyridinium complexes and Pd/TiO2 catalysts were successfully used as the catalytic system for the photo catalytic reduction of water and carbon dioxide to hydrogen and methane respectively. Phosphonate-tethered Ru(II)-quaterpyridinium complexes were synthesized from Ru(II)-tris-quaterpyridyl complexes. These complexes form stable adhesive layers on indium tin oxide (ITO) electrodes. A series of differential pulse voltammetry experiments were carried out to measure the ground state and excited state redox potentials of all the Ru(II)quaterpyridinium complexes. The reductive potentials obtained were compared with the reductive potentials of CO2 to CH4 and H2O to H2 reductions. The measurements obtained from the experiments confirmed that it is possible to thermodynamically oxidize water and reduce CO2 by using phosphonate-tethered Ru(II)-quaterpyridinium complexes. These complexes are successfully utilized as prototypes for mycobacterial channel blockers. The Ru(II) complexes show distinct changes in their luminescence spectra when bound to the porin MspA from M. smegmatis, which is a non-pathogenic relative of M. tuberculosis. By using HPLC, we have determined binding constants of the Ru(II)-complexes to MspA in phosphate buffer (0.05 M, pH = 6.8) ranging from 5.2 x 109 M-1 (Ru-C2) to 1.8 x 109 M-1 (Ru-C4). Our findings indicate that channel blocking is a promising treatment strategy for mycobacterial infections. Poly-N-isopropyl-acrylamide/acetic acid copolymers were synthesized and characterized by elemental analysis and gel permeation chromatography. The average composition of the copolymers determined from CHN analysis is in excellent correlation with the feed composition indicating that the radical polymerization process is indeed statistical. Crosslinking of individual polymer chains permitted the generation of ultraflat layers on Mica surfaces by a simple spin-casting procedure, which are able to host the mycobacterial channel protein MspA, while retaining its channel function.

<p>Artificial systems involving water oxidation and solar cells are promising ways for the conversion of solar energy into fuels and electricity. These systems usually consist of a photosensitizer, an electron donor and / or an electron acceptor. This thesis deals with the synthesis and photoinduced electron transfer of several donor-sensitizer-acceptor supramolecular systems.</p><p>The first part of this thesis describes the synthesis and properties of two novel dinuclear ruthenium complexes as electron donors to mimic the donor side reaction of Photosystem II. These two Ru₂ complexes were then covalently linked to ruthenium trisbipyridine and the properties of the resulting trinuclear complexes were studied by cyclic voltammetry and transient absorption spectroscopy.</p><p>The second part presents the synthesis and photoinduced electron transfer of covalently linked donor-sensitizer supramolecular systems in the presence of TiO₂ as electron acceptors. Electron donors are tyrosine, phenol and their derivatives, and dinuclear ruthenium complexes. Intramolecular electron transfer from the donor to the oxidized sensitizer was observed by transient absorption spectroscopy after light excitation of the Ru(bpy)₃²⁺ moiety. The potential applications of Ru₂-based electron donors in artificial systems for water oxidation and solar cells are discussed.</p><p>In the final part, the photoinduced interfacial electron transfer in the systems based on carotenoids and TiO₂ is studied. Carotenoids are shown to act as both sensitizers and electron donors, which could be used in artificial systems to mimic the electron transfer chain in natural photosynthesis.</p>

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