Refine
Has Fulltext
- yes (25)
Is part of the Bibliography
- yes (25) (remove)
Year of publication
Document Type
- Doctoral Thesis (25)
Keywords
- Flüssigkristall (4)
- Chemistry (2)
- Chromophor (2)
- Columnare Phase (2)
- Diamant (2)
- Dyade (2)
- Flüssigkristalle (2)
- Fotokatalyse (2)
- Fullerene (2)
- Knochenzement (2)
- Liquid Crystals (2)
- Mesogen (2)
- Nanosegregation (2)
- Raumfüllung (2)
- Squaraine (2)
- Sternmesogene (2)
- Thermotroper Flüssigkristall (2)
- A-D-A dyes (1)
- Alkaloid (1)
- Alkaloide (1)
- Amino Acids (1)
- Aminosäuren (1)
- Ancistrocladaceae (1)
- Ancistrocladus (1)
- Anthracenderivate (1)
- Anthrachinonderivate (1)
- Anti-infectious activity (1)
- Antiausterity activity (1)
- Aromaten (1)
- Aromatic Systems (1)
- Artificial photosynthesis (1)
- Beschichtung (1)
- Bioisosterie (1)
- Bodipy (1)
- Bor (1)
- Boron (1)
- Boron Chemistry (1)
- Borverbindungen (1)
- Borylencarbonyle (1)
- Borylene (1)
- C/Si-Austausch (1)
- CVD-Diamant (1)
- Calciumhydroxid (1)
- Calciumphosphat (1)
- Calciumphosphate (1)
- Calciumphosphatzemente (1)
- Carbenes (1)
- Carbon Nanotube (1)
- Catalysis (1)
- Ceramic polymer composite (1)
- Chelatbildner (1)
- Congo (1)
- Detonationsdiamant (1)
- Dimer (1)
- Dimere (1)
- Dipolare Cycloaddition (1)
- Distickstoff (1)
- Distickstoff Aktivierung (1)
- Distickstoff Spaltung (1)
- Donor-Akzeptor-Dyaden (1)
- Dual setting system (1)
- Dyad (1)
- Dünne Schicht (1)
- Elektronentransfer (1)
- Endorezeptor (1)
- Energieaufnahme (1)
- Energy Transfer (1)
- Evaporation-Induced Self-Assembly (1)
- Excitons (1)
- Exziton (1)
- Festphasenpeptidsynthese (1)
- Fluorescence (1)
- Fluoreszenz (1)
- Fotovoltaik (1)
- Freiraumfüllung (1)
- Fulleren (1)
- Fulleren-Netzwerk (1)
- Funktionalisierung <Chemie> (1)
- Germanium (1)
- Halbleiter (1)
- Hekate (1)
- Heterosolarzelle (1)
- Hexaarylbenzene (1)
- Hydrogel (1)
- Immobilisiertes Enzym (1)
- Implantat (1)
- Iridium-Photosensibilisator (1)
- Isolation (1)
- Isolierung (1)
- Isolierung <Chemie> (1)
- J-Aggregate (1)
- Katalysatorimmobilisierung (1)
- Knochenkleber (1)
- Knochenwachs (1)
- Kohlenmonoxid (1)
- Kohlenstoff-Nanoröhre (1)
- Kohlenstoffmonoxid (1)
- Kohlenstoffnanozwiebel (1)
- Kolloid / Lösung <Chemie> (1)
- Kongo (1)
- Krebs <Medizin> (1)
- Ligand design (1)
- Liquid Crystal (1)
- Lumineszenz (1)
- Magnesiumphosphate (1)
- Maiglöckchen (1)
- Merocyanine (1)
- Nanodiamant (1)
- Nanopartikel (1)
- Naphthylisochinolinalkaloide (1)
- Naphthylisoquinolin (1)
- Naphthylisoquinoline (1)
- Natural Products (1)
- Nematische Phase (1)
- Organic Chemistry (1)
- Organische Chemie (1)
- Organokatalyse (1)
- Pancreatic cancer (1)
- Perylenbisimide (1)
- Perylenderivate (1)
- Perylene Bisimide (1)
- Perylene Bisimides (1)
- Phosphorescence (1)
- Photosensibilisator (1)
- Phthalocyanin (1)
- Porphyrin (1)
- Protonenreduktion (1)
- Pyrenderivate (1)
- Pyrene (1)
- Rhodium (1)
- Riechstoff (1)
- Ruthenium-Photosensibilisator (1)
- Rutheniumkomplexe (1)
- Selbstorganisation (1)
- Sila-Substitution (1)
- Silicium (1)
- Siliciumorganische Verbindungen (1)
- Solid Phase Peptide Synthesis (1)
- Sonogashira (1)
- Sonogashira coupling (1)
- Sonogashira-Hagihara-Reaktion (1)
- Space filling (1)
- Sternmesogen (1)
- Structural elucidation (1)
- Strukturaufklärung (1)
- Supramolekül (1)
- Synthesediamant (1)
- Transition Metals (1)
- V-förmige Mesogene (1)
- V-shaped mesogens (1)
- Verbundwerkstoff (1)
- Verdunstung (1)
- Wasserstofferzeugung (1)
- Wirt-Gast-Mesogen (1)
- Zinn (1)
- [FeFe] hydrogenase mimic (1)
- [FeFe]-Hydrogenase Imitator (1)
- antibacterial (1)
- antibakteriell (1)
- biaxial nematogens (1)
- biaxiale Nematogene (1)
- bioisosterism (1)
- board-shaped mesogens (1)
- bohrbar (1)
- bone adhesive (1)
- bone wax (1)
- bourgeonal (1)
- brettförmige Mesogene (1)
- cAAC (1)
- calciumhydroxide (1)
- coating (1)
- damascone (1)
- drillable (1)
- dual abbindend (1)
- dual setting (1)
- dyad (1)
- dyads (1)
- dünner Filme (1)
- endoreceptor (1)
- fullerene network (1)
- galaxolide (1)
- galbanone (1)
- host-guest mesogen (1)
- implant (1)
- iridium photosensitizer (1)
- lilial (1)
- merocyanines (1)
- n-type semiconductors (1)
- nanodiamond (1)
- nanosegregation (1)
- niedervalente Borverbindungen (1)
- organic solar cells (1)
- premixed (1)
- proton reduction (1)
- präfabriziert (1)
- ruthenium photosensitizer (1)
- space filling (1)
- star mesogen (1)
- thin film (1)
- verdunstungsinduzierter Selbstanordnung (1)
- Übergangsmetall (1)
- Übergangsmetallkomplexe (1)
Institute
Sonstige beteiligte Institutionen
Synthese und Charakterisierung neuartiger Silicium-, Germanium- und zinnorganischer Riechstoffe
(2014)
Aufbauend auf dem Konzept der C/Si-Bioisosterie beschreibt die vorliegende Arbeit die Synthese und Charakterisierung siliciumhaltiger Derivate der Riechstoffe Galaxolide, Lilial, Bourgeonal, 5,7,7-Trimethyl-4-methylenoctanal und α-Galbanone sowie Beiträge zur Synthese eines silicium¬haltigen Derivats von δ-Damascone. Basierend auf der C/Ge- und C/Sn-Bioisosterie wurden zudem die Germa- und Stanna-Analoga von Lilial und Bourgeonal synthetisiert. Die entsprechenden Zielverbindungen sowie alle isolierten Zwischenstufen wurden durch NMR-Spektroskopie (1H, 11B, 13C, 15N, 29Si, 119Sn) und Elementaranalyse (C, H, N) charakterisiert. In einigen Fällen erfolgte zusätzlich eine Charakterisierung durch Einkristall-Röntgenstrukturanalyse oder Infrarot-Spektroskopie.
This thesis established the fabrication of organic solar cells of DA dye donors and fullerene acceptors under ambient conditions in our laboratory, however, with reduced power conversion efficiencies compared to inert conditions. It was shown that moisture had the strongest impact on the stability and reproducibility of the solar cells. Therefore, utilization of robust materials, inverted device architectures and fast fabrication/characterization are recommended if processing takes place in air. Furthermore, the dyad concept was successfully explored in merocyanine dye-fullerene dyads and power conversion efficiencies of up to 1.14 % and 1.59 % were measured under ambient and inert conditions, respectively. It was determined that the major drawback in comparison to comparable BHJ devices was the inability of the dyad molecules to undergo phase separation. Finally, two series of small molecules were designed in order to obtain electron transport materials, using the acceptor-core-acceptor motive. By variation of the acceptor units especially the LUMO levels could be lowered effectively. Investigation of the compounds in organic thin film transistors helped to identify promising molecules with electron transport properties. Electron transport mobilities of up to 7.3 × 10−2 cm2 V−1 s−1 (ADA2b) and 1.39 × 10−2 cm2 V−1 s−1 (AπA1b) were measured in air for the ADA and AπA dyes, respectively. Investigation of selected molecules in organic solar cells proved that these molecules work as active layer components, even though power conversion efficiencies cannot compete with fullerene based devices yet. Thus, this thesis shows new possibilities that might help to develop and design small molecules as substitutes for fullerene acceptors.
Herein described is the discovery of three novel types of dimeric naphthylisoquinoline alkaloids, named mbandakamines, cyclombandakamines, and spirombandakamines. They were found in the leaves of a botanically as yet unidentified, potentially new Ancistrocladus species, collected in the rainforest of the Democratic Republic of the Congo (DRC). Mbandakamines showed an exceptional 6′,1′′-coupling, in the peri-position neighboring one of the outer axes, leading to an extremely high steric hindrance at the central axis, and to U-turn-like molecular shape, which – different from all other dimeric NIQs, whose basic structures are all quite linear – brings three of the four bicyclic ring systems in close proximity to each other. This created an unprecedented follow-up chemistry, involving ring closure reactions, leading to two further, structurally even more intriguing subclasses, the cyclo- and the spirombandakamines, displaying eight stereogenic elements (the highest total number ever found in naphthylisoquinoline alkaloids). The metabolites exhibited pronounced antiplasmodial and antitrypanosomal activities. Likewise reported in this doctoral thesis are the isolation and structural elucidation of naphthylisoquinoline alkaloids from two further potentially new Ancistrocladus species from DRC. Some of these metabolites have shown pronounced antiausterity activities against human pancreatic cancer PANC-1 cells.
Calcium phosphate cements (CPC) represent valuable synthetic bone grafts, as they are self-setting, biocompatible, osteoconductive and in their composition similar to the inorganic phase of human bone. Due to their long shelf-life, neutral setting and since water is sufficient for setting, hydroxyapatite (HA) forming cements are processed in different paste formulations. Those comprise dual setting, Ca2+ binding and premixed cement systems. With dual setting formulations, both dissolution and precipitation of the cement raw powder occur simultaneously to the polymerization of water-soluble monomers to form a hydrogel. Chelating agents are able to form complexes with Ca2+ released from the raw powder. Premixed systems mostly contain the raw powder of the cement and a non-aqueous binder liquid which delays the setting reaction until application in the moist physiological environment. In the present work, two of those reaction mechanisms allowed the development of HA based cement applications.
Drillable cements are of high clinical interest, as the quality of screw and plate osteosynthesis techniques can be improved by cement augmentation. A drillable, dual setting composite from HA and a poly(2-hydroxyethyl methacrylate) hydrogel was analyzed with respect to the influence of monomer content and powder-to-liquid ratio on setting kinetics and mechanical outcome. While the conversion to HA and crystal growth were constantly confined with increased monomer amount, a minimum concentration of 50 % was required to see impressive ameliorations including a low bending modulus and high fracture energy at improved bending strength. Increasing the liquid amount enabled injection of the paste as well as drilling after 10 min of pre-setting.
While classic bone wax formulations have drawbacks such as infection, inflammation, hindered osteogenesis and a lack of biodegradability, the as-presented premixed formulation is believed to exhibit outmatching properties. It consisted of HA raw powders and a non-aqueous, but water-miscible carrier liquid from poly(ethylene glycol) (PEG). The bone wax was proved to be cohesive and malleable, it withstood blood pressure conditions and among deposition in an aqueous environment, PEG was exchanged such that porous, nanocrystalline HA was formed. Incorporation of a model antibiotic proved the suitability of the novel bone wax formulation for drug release purposes.
Prefabricated laminates from premixed carbonated apatite forming cement and poly(ε-caprolactone) fiber mats with defined pore architecture were presented as a potential approach for the treatment of 2-dimensional, curved cranial defects. They are flexible until application and were produced in a layer-by-layer approach from both components such that the polymer scaffold prevents the cement from flowing. It was demonstrated that solution electrospinning with a patterned collector for the fabrication of perforated fiber mats was suitable, as high fiber volume contents in combination with an appropriate interface enabled the successful fabrication of mechanically reinforced laminates. Mild immersion of the scaffolds under alkaline conditions additionally improved the interphase followed by an increase in bending-strength.
Since few years, magnesium phosphate cements (MPC) have attracted increasing attention for bone replacement. Compared to CPC, MPC exhibit a higher degradation potential and high early strength and they release biologically valuable Mg2+. However, common systems offer some challenges while using them in non-classic cement formulations such as the need for foreign ion supply, the potential acidity of the reaction or the fast setting kinetics. Here, it was possible to develop a chelate-setting MPC paste with a broad spectrum of potential applications.
The general mechanism of the novel setting principle was tested in a proof-of-principle manner. The cement paste consisted of farringtonite with differently concentrated phytic acid solution for chelate formation with Mg2+ from the raw powder. Adjusting the phytic acid content and adding a magnesium oxide as setting regulator to compensate its retarding effect resulted in drillable formulations. Additionally, there is a strong clinical demand for well working bone adhesives especially in a moist environment. Mostly the existing formulations are non-biodegradable. Ex vivo adhesion of the above presented MPC under wet conditions on bone demonstrated over a course of 7 d shear strengths of 0.8 MPa. Further, the hardened cement specimens showed a mass loss of 2 wt.% within 24 d in an aqueous environment and released about 0.17 mg/g of osteogenic Mg2+ per day. Together with the demonstrated cytocompatibility towards human fetal osteoblasts, this cement system showed promising characteristics in terms of degradable biocements with special application purposes.
Einfach Lewis-Basen stabilisierte Borylene wurden durch Reduktion in situ hergestellt und in Gegenwart von Kohlenstoffmonoxid oder Distickstoff umgesetzt. Die entstandenen Verbindungen wurden mittels NMR-, ESR-, UV/Vis- und IR-Spektroskopie sowie Einkristallröntgenstrukturanalyse charakterisiert. Im Zuge dessen konnten für die erhaltenen Spezies Eigenschaften ermittelt werden, die denen analoger Übergangsmetallkomplexe ähneln. Ferner konnten die zugrundeliegenden mechanistischen Vorgänge der Reaktionen durch gezielte Variation der Reaktionsparameter aufgeklärt werden. Zudem wurden Redoxverhalten und Reaktivitäten der isolierten Produkte in weiterführenden Studien näher untersucht.
Thus, the main focus of this thesis was to generate and investigate new one-dimensional LC PBI J-aggregates of an entirely new PBI organization with the transition dipole moments of the chromophores arranged parallel to the columnar axis and in slipped pi-pi stacking fashion to form highly fluorescent J-aggregates. Towards this goal, the tetra-bay substituted PBI 4c bearing free NH functional groups at the imide positions and four dendrons with branched ethylhexyl alkoxy chains at the meta-position of the phenoxy spacer (Figure 8.1a) was synthesized and compared to a literature known reference PBI 1. The mesogenic dendrons ensure LC character of the dye, which was confirmed by POM, DSC and extensive X-ray analysis. Furthermore, the sterically demanding bay-substituents prevent the cofacial assembly of the chromophores and force the dyes into a slipped pi-stacked order with the main transition dipole moments of the dyes oriented parallel to the columnar axis. X-ray analysis revealed that PBI 4c assembles into columnar triple-stranded helices consisting of side-to-side stacked molecules, which organize into a Colh phase (Figure 8.1b). FT-IR experiments of a thin film and aggregates in MCH solution confirmed the formation of H-bonds between the imide moieties. Temperature-dependent investigations furthermore proved a reversible formation of H-bonds and polarized FT-IR experiments finally gave evidence for the direction of the H-bonds along the shearing respective the columnar axis (Figure 8.1c). This was additionally verified by polarized UV-Vis absorption studies of aligned thin films. The changes in the UV-Vis absorption spectra of concentration- and temperature-dependent experiments in MCH are in agreement with the formation of J-aggregates and could be fitted to a nucleation-elongation growth mechanism. Remarkably, fluorescence spectroscopy studies revealed highly emissive aggregates in solution. These various spectroscopic techniques proved the utilization of directional noncovalent forces like hydrogen-bonding and pi-pi interactions in a cooperative manner forcing the PBI molecules in an unprecedented organization of a slipped pi-stacked arrangement with the orientation of the molecular axis and the respective transition dipole moments parallel to the columns of the LC phase. By the group of Dietrich the formation of exciton-polaritons in imprinted LC pillar microcavities as consequent use of the LC 4c was reported for the first time.In the second part of this thesis the hierarchical organization of LC PBIs into defined single-, double-, triple- and quadruple-stranded J-aggregates within crystalline and columnar LC phases, partially arranged in helical supramolecular structures in dependence of the molecular design was demonstrated. This was achieved via the preparation of a library of twelve molecules PBI 3-6(a-c) (Figure 8.2a) that was synthesized by varying the substitution position of the dendrons at the phenoxy-spacer from ortho to meta or para and by introducing an additional methyl group in ortho-position. Also the length and shape of the alkoxy chains was changed. Consequently, the impact of the sterical demand of the bay substituents concerning their phase properties, molecular arrangement and exciton coupling was investigated. POM, DSC and X-ray studies revealed the formation of only crystalline phase for the ortho-substituted PBIs 3a-c, whereas the other derivatives generated SC or LC phases. The main focus was the series with the n-C12-alkoxy chains. For the corresponding PBIs 4-6b columnar LC phases were confirmed. Retrostructural analysis by modelling and simulations gave indications for a single stranded organization for PBI 3b, a double-stranded helix for PBI 6b, a triple-stranded helical arrangement for PBI 5b and a quadruple-stranded helix for PBI 4b (Figure 8.2b-d). For all four derivatives the same molecular orientation within the columns as for PBI 4c was proven by polarized FT-IR and UV-Vis absorption studies in aligned thin films. The organization in helices of different number of strands in the Cr and LC phases of PBI 3b, 4b, 5b and 6b offered a unique possibility to elucidate the influence of particular packing arrangements on dye aggregate interactions with light. In particular, it can be investigated how exciton coupling of the dyes’ transition dipole moments and fluorescence properties are affected. In this context, the spectroscopic properties were investigated in thin film, which revealed a strong bathochromic shift of the absorption maxima compared to the monomers in solution in dependence on the number of strands for PBIs 4-6b in contrast to PBI 3b (Figure 8.2e). The same tendency was observed for the respective aggregates in MCH solution. The spectral changes obtained during concentration- and temperature-dependent UV-Vis absorption studies verified the formation of J-aggregates in MCH solution and solid state. The respective aggregates are highly likely formed via a nucleation-elongation growth mechanism. Appliance of Kasha’s exciton theory on the supramolecular aggregates revealed different contributions of H- and J-type coupling for the oligo-stranded helices. Under these considerations, it delivered an explanation for the absorption and fluorescence properties of the assemblies and declares the “best” J-aggregate for the double stranded arrangement of PBI 6b with purely negative couplings among neighbour molecules and a quantum yield above 74 % of the aggregates in MCH solution. With this H-bonded PBI-based library approach of twelve derivatives it could be shown how molecular engineering of perylene bisimide dyes can be used to design defined, complex supramolecular assemblies with unprecedented packing patterns and concomitant intriguing spectroscopic properties.
So far, the formation of defined liquid crystalline supramolecular structures of tetra-bay substituted PBIs by double H-bonding between free imide moieties and pi-pi interactions between the chromophores was demonstrated. The impact of the H-bonds on the molecular arrangement was investigated in the next part of this thesis. In this regard, PBIs 7 and 8 bearing a methyl or cyclohexyl group at the imide position (Figure 8.3a) were synthesized and compared to PBI 4c. The soft character of the solid state for PBIs 7 and 8 was confirmed by POM, DSC and X-ray analysis. The X-ray studies further revealed for both PBIs a change of the molecular assembly towards helical columnar structures of conventional pi-stacked chromophores (Figure 8.3b) when the directed H-bonds cannot contribute as noncovalent interactions to the assembly formation. Temperature-dependent UV-Vis absorption studies demonstrated the importance of H-bonding in MCH solution in the way that the formation of J-aggregates as for PBI 4c could not be observed for the imide substituted molecules. In the next step, the spectroscopic properties in thin film were investigated. For PBI 7 a J-type band and fluorescence spectra with an enlarged Stokes shift and increased fluorescence lifetime of 11.4 ns, compared to PBI 4c, was obtained, suggesting the generation of excimer type emission by considering the assumed conventional stacking of rotational displaced molecules from X-ray analysis. With polarized UV-Vis absorption experiments the orientation of the molecules perpendicular to the shearing direction and subsequently to the columnar axis was confirmed. These diverse investigations clearly demonstrated the imperative of H-bonds for stable, defined, LC J-aggregates with the transition dipole moments parallel to the columnar axis. With PBIs 7 and 8 it is impressively shown how small changes in the molecular structure influence the molecular arrangement dependent on the cooperation of non-covalent interactions like H-bonding and pi-pi stacking.
In the last part of this thesis the generation of two-dimensional LC arrangements is presented. Since tetra-bay substituted PBIs lead always to twisted cores preventing lamellar arrangement, here 1,7-disubstitution and the simultaneous retention of the free imide positions was chosen to generate LC lamellar phases of PBIs 9a, 9b and 10 (Figure 8.4a). This molecular design was expected to form planar perylene cores that can strongly interact by pi-pi stacking and H-bonding. POM, DSC and X-ray investigations of the compounds suggest lamellar LC phases for PBIs 9a and 9b and a soft phase for PBI 10. In this regard, the goal of the formation of LC lamellar phase of PBIs could be attained. The change from dendrons with n-C12-alkoxy chains to large fork-like mesogens like in 9b clearly changed the phase properties. PBI 9b exhibits the lowest clearing point, high phase stability, least viscosity, easy shearability at room temperature and phase transitions between lamellar and Colh phases dependent on temperature. The formation of H-bonds parallel to the layers was demonstrated by polarized FT-IR experiments for all three PBIs. Concentration-dependent UV-Vis absorption studies revealed the formation of a J-type aggregate, which seems to exhibit an overall two-dimensional structure. With STM investigations the formation of lamellar structures from drop-casted 9a and 10 solutions in 1-phenyloctane on HOPG surface could be observed. Figure 8.4b illustrates a schematic possible arrangement of the molecules in the layers (here exemplarily demonstrated for PBI 9a), which has to be further confirmed by modelling and simulations. Unfortunately, fluorescence investigations of the thin films revealed non- or only slightly emissive LC states, which make them negligible for photonic applications. Nevertheless, the synthesized and analyzed compounds might be an inspiration for further investigations on the path to two-dimensional exciton transport for photonic devices.
This thesis investigates different ligand designs for Ru(II) complexes and the activity of the complexes as photosensitizer (PS) in photocatalytic hydrogen evolution. The catalytic system typically contains a catalyst, a sacrificial electron donor (SED) and a PS, which needs to exhibit strong absorption and luminescence, as well as reversible redox behavior. Electron-withdrawing pyridine substituents on the terpyridine metal ion receptor result in an increase of excited-state lifetime and quantum yield (Φ = 74*10-5; τ = 3.8 ns) and lead to complex III-C1 exhibiting activity as PS. While the turn-over frequency (TOFmax) and turn-over number (TON) are relatively low (TOFmax = 57 mmolH2 molPS-1 min-1; TON(44 h) = 134 mmolH2 molPS-1), the catalytic system is long-lived, losing only 20% of its activity over the course of 12 days. Interestingly, the heteroleptic design in III-C1 proves to be beneficial for the performance as PS, despite III-C1 having comparable photophysical and electrochemical properties as the homoleptic complex IV-C2 (TOFmax = 35 mmolH2 molPS-1 min-1; TON(24 h) = 14 mmolH2 molPS-1). Reductive quenching of the excited PS by the SED is identified as rate-limiting step in both cases.
Hence, the ligands are designed to be more electron-accepting either via N-methylation of the peripheral pyridine substituents or introduction of a pyrimidine ring in the metal ion receptor, leading to increased excited-state lifetimes (τ = 9–40 ns) and luminescence quantum yields (Φ = 40–400*10-5). However, the more electron-accepting character of the ligands also results in anodically shifted reduction potentials, leading to a lack of driving force for the electron transfer from the reduced PS to the catalyst. Hence, this electron transfer step is found to be a limiting factor to the overall performance of the PS. While higher TOFmax in hydrogen evolution experiments are observed for pyrimidine-containing PS (TOFmax = 300–715 mmolH2 molPS-1 min-1), the longevity for these systems is reduced with half-life times of 2–6 h.
Expansion of the pyrimidine-containing ligands to dinuclear complexes yields a stronger absorptivity (ε = 100–135*103 L mol-1 cm-1), increased luminescence (τ = 90–125 ns, Φ = 210–350*10-5) and can also result in higher TOFmax given sufficient driving force for electron transfer to the catalyst (TOFmax = 1500 mmolH2 molPS-1 min-1). When comparing complexes with similar driving forces, stronger luminescence is reflected in a higher TOFmax. Besides thermodynamic considerations, kinetic effects and electron transfer efficiency are assumed to impact the observed activity in hydrogen evolution. In summary, this work shows that targeted ligand design can make the previously disregarded group of Ru(II) complexes with tridentate ligands attractive candidates for use as PS in photocatalytic hydrogen evolution.
The purpose of the present work was, in the first part, to investigate the potential of iron-based metal complexes in catalytic borylation reactions with alkyl halides as substrates and B2pin2 as the borylation reagent. Moreover, extended studies of the recently reported, copper mediated borylation reactions of aryl halides were performed, including the screening of substrates and alkoxy bases as well as ligand-screening. Investigations were undertaken on the role of Cu-nanoparticles, which might be involved in this catalytic reaction. Furthermore, Cu-phosphine complexes were synthesized as precursors, but attempts to isolate Cu-boryl species which are intermediates in the proposed catalytic cycle were unsuccessful, although 11B NMR evidence for a Cu-boryl complex was obtained.
In the second part of this work, the alternative, Lewis-acidic diboron(4) compound bis(ethylene glycolato)diboron (B2eg2) was synthesized to compare its reactivity with the reactivity of other diboron(4) compounds (e.g. B2neop2, B2cat2, B2pin2 and B2(NMe2)4). Therefore, reactions of B2eg2 with different Lewis-bases, such as NHCs and phosphines, were performed to investigate the possible formation of sp2-sp3 or sp3-sp3 adducts and ring-expansion reactions (RERs).
The aim was to obtain a better general insight into the reactivity of diboron(4) compounds with Lewis-bases because they are both used as reactants in transition metal-catalyzed and metal-free borylation reactions. Understanding the B–B bond activation process promoted by Lewis-bases provides a new perspective on the reaction pathways available for various borylation reactions.
Herstellung und Charakterisierung kolloidaler Lösungen diamantbasierter und verwandter Materialien
(2022)
In der vorliegenden Publikation wurden stabile kolloidale Lösungen aus CVD-Diamant, Detonationsdiamant sowie artverwandten Materialien hergestellt und charakterisiert
Besonderes Augenmerk wurde bei der Zerkleinerung von CVD Diamant daraufgelegt, dass die nanoskaligen Partikel ihre materialspezifischen Eigenschaften auch bei Reduktion der Größe beibehalten.
Systematisch wurde die Zerkleinerung in einer Planetenmühle analysiert. Es wurde sowohl die minimal erreichbare Partikelgröße, als auch die Menge an erzeugtem, nanoskaligem Material bewertet.
Um die Vermahlung zu verbessern, wurden die Geschwindigkeit der Mühle, die Größe der Mahlkörper, die Dauer der Vermahlung, sowie die eingesetzten Lösemittel variiert. Des Weiteren konnten durch die Vermahlung unterschiedlich hergestellter CVD Diamantfilme in einer Vibrationsmühle die Einflüsse von Schichtdicke und Korngröße der Diamantkristalle untersucht werden.
Durch Bearbeitung von Detonationsdiamanten und Kohlenstoffnanozwiebeln wurden stabile kolloidale Lösungen hergestellt, mit Partikelgrößen im unteren Nanometerbereich. Diese sind im alkalischen pH-Bereich stabil sein, hierfür wurde durch Luft und Säureoxidation oxidierter Detonationsdiamant und oxidierte Kohlenstoffnanozwiebeln hergestellt. Mithilfe der thermogravimetrischen Analyse und Infrarotspektroskopie wurde die hierfür optimale Temperatur und Dauer bestimmt.
In summary, we have prepared single-wall carbon nanotube (SWNT) thin films by the method of evaporation-induced self-assembly (EISA). Using the scalable two-plate or lens setups, sorts of different film types or patterns of SWNTs has been successfully fabricated directly from the evaporation of solvents and could be precisely controlled by the concentrations of SWNT in ambient conditions. The special geometry of meniscus as the capillary bridge has not only given rise to a much higher efficiency of fabrication than what previously reported but also allowed us to monitor the pinning and depinning process carefully and further investigate the mechanism underlying the formation of different film morphologies.
In contrast with the conventional "stick-slip" model, we have provided the new dynamical pinning and zipping model for the contact line (CL) behavior. By analyzing the motion of CL and varying deposited patterns, the traditionally so-called "stick" state should be treated as a dynamical pinning process due to the interfacial tension contrast between SWNT-covered and bare silicon surface. Besides, the plausible one-step "slip" motion could be dominated by the zipping-like kink propagation.
In addition, the experiments with heated substrates at higher temperatures between 30°C and 50 °C have shown that the striped pattern could be fabricated by both much lower SWNT and SDS concentrations than that in room temperature, which is consistent with our model of interfacial tension contrast. In this situation, the deposition rate was increased but the quality of SWNT alignment was undermined because the corresponding moving velocity of SWNT was also too fast for SWNTs to rotate when the evaporative rate was high.
The similar results were identified by the SWNT/polymer conjugates dispersed in chloroform under the similar setups and other identical conditions. The typical breathing motion of dynamical pinning and zipping-like propagation for depinning were confirmed by the new suspensions despite that some morphological parameters changed dramatically compared with that from the aqueous solution. For example, the spacing between stripes reached 100 µm ~ 200 µm because the large contact angle contrast between HDMS- and SWNT-covered surface accompanies with the high evaporation rate of chloroform in the pinning and depinning process. Likewise the average CL velocity for fabrication reached around 20 µm/s due to the much higher evaporation rate of chloroform than water.
Using alike suspensions, the modified EISA method called dose-controlled floating evaporative self-assembly (DFES) was employed to implement the self-assembly of SWNTs on the water/air interface and then deposit them on solid substrate by directed floating. Although the stripes were fabricated successfully by drops with certain doses and SWNT concentrations, there inevitably existed randomly oriented SWNTs from the water surface that built networks between the stripes containing well-aligned tubes. In order to slow down the evaporation rate and monitor the process detailedly, we used chlorobenzene as the solvent instead of chloroform and find the typical pinning/depinning movement of the CL. A preliminary analysis of the results in terms of chlorobenzene implied that the CL possibly followed the similar pinning/depinning process in consistence with our model with capillary bridge.
In the last part of the thesis, the primary research on the optical properties of these stripes of ultrahigh purity semiconducting nanotubes was conducted by fluorescence microscopy and photoluminescence excitation (PLE) spectroscopy. The energy transfer of the photogenerated excitons was confirmed between different tube species with controlled band gaps.
In short, the experiments performed in this thesis allowed to gain new insights about the fabrication of large-area SWNT thin films by the cost-effective solution-processed method and most importantly to uncover its intrinsic mechanism as well. Combined with the separation and selection technique like density gradient centrifugation or polyfluorene derivatives assisted method, highly monodisperse semiconducting nanotubes could be deposited into organized, controllable and functional arrays.
Beyond the ambient conditions, precise control for the evaporation under preset temperature and vapor pressure could possibly extend the technique to the industry level. Assisted by some other mature techniques such as roll-to-roll printing, the cost-effective method could be widely used in the manufacture of various thin film devices. More complex 2D or even 3D structures could be designed and accomplished by the method for the functional or stretchable requirements. Further research on the fundamental exciton transition and diffusion in different networks or structures of SWNTs will be the significant precondition for the real applications.
Looking ahead, from the individual carbon nanotube to its thin film, this promising material with outstanding properties had many challenges to overcome before the real-world applications. Thanks to the availability of pure and well-defined materials, the scalable solution-processed approaches for fabrication of thin films should be able to unlock the potential of carbon nanotubes and exploit them in (opto-)electronic devices in the foreseeing future.