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Fully conjugated porphyrin nanorings combine an end-free π-system with well defined size and shape. They provide models for testing our understanding of light harvesting in natural photosynthetic systems, and may lead to the creation of new functional materials. This thesis describes the template-directed synthesis of novel 10, 16, 18, 20, 24, 30, 40 and 50-porphyrin nanorings using small templates, as well as the investigation of their structure, electronic properties and supramolecular chemistry in solution and on surfaces. This work illustrates the scope of Vernier templating as a tool for the synthesis of monodisperse molecules of unprecedented sizes. Chapter 1 introduces key properties of porphyrins and π-conjugated linear and cyclic porphyrin oligomers and describes the principle methods of preparing non-conjugated and conjugated cyclic polymers. It also covers recent advances in the synthesis of fully-conjugated porphyrin nanorings, in particular Vernier templating. Chapter 2 discusses the formation of higher order porphyrin nanorings (18- and 24-porphyrin nanorings) in the classical synthesis of 6-porphyrin nanoring and the Vernier-templated synthesis of 12-porphyrin nanoring. Chapter 3 describes the Vernier-templated synthesis of 24-porphyrin nanoring and its characterization. Chapter 4 shows that the flexibility of 24-porphyrin nanoring can be locked by the formation of a “sandwich” complex in the presence of a bidentate ligand or by solvent-induced formation of aggregates. Chapter 5 demonstrates the use of templates to control the cyclooligomerization of linear porphyrin oligomers. Vernier-templated synthetic routes to 10-, 30- and 40-porphyrin nanorings are investigated. Chapter 6 reports the electronic properties of porphyrin nanorings as probed by electrochemistry (for 6 porphyrin nanoring) or fluorescence anisotropy measurements (for 24 porphyrin nanoring). Crystal structures of 6 and 12 porphyrin nanoring template complexes are presented. Chapter 7 contains experimental procedures and characterization data of known and novel compounds synthesized in the course of this thesis.

Yes / The physical properties of cyclic and linear polymers are markedly different; however, there are few examples which exploit these differences in clinical applications. In this study, we demonstrate that self-assemblies comprised of cyclic-linear graft copolymers are significantly more stable than the equivalent linear-linear graft copolymer assemblies. This difference in stability can be exploited to allow for triggered disassembly by cleavage of just a single bond within the cyclic polymer backbone, via disulfide reduction, in the presence of intracellular levels of l-glutathione. This topological effect was exploited to demonstrate the first example of topology-controlled particle disassembly for the controlled release of an anti-cancer drug in vitro. This approach represents a markedly different strategy for controlled release from polymer nanoparticles and highlights for the first time that a change in polymer topology can be used as a trigger in the design of delivery vehicles. We propose such constructs, which demonstrate disassembly behavior upon a change in polymer topology, could find application in the targeted delivery of therapeutic agents. / ERC are acknowledged for support to M.C.A., A.P.D. (grant number: 681559) and R.O.R. (grant number: 615142).

Yes / The synthesis of cyclic amphiphilic graft copolymers with a hydrophobic polycarbonate backbone and hydrophilic poly(N-acryloylmorpholine) (PNAM) side arms via a combination of ring-opening polymerization (ROP), cyclization via copper-catalyzed azide–alkyne cycloaddition (CuAAC), and reversible addition–fragmentation chain transfer (RAFT) polymerization is reported. The ability of these cyclic graft copolymers to form unimolecular micelles in water is explored using a combination of light scattering, small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryoTEM) analyses, where particle size was found to increase with increasing PNAM arm length. Further analysis revealed differences in the solution conformations, loading capabilities, and morphologies of the cyclic graft copolymers in comparison to equivalent linear graft copolymer unimolecular micelle analogues. Furthermore, the cyclic and linear graft copolymers were found to exhibit significantly different cloud point temperatures. This study highlights how subtle changes in polymer architecture (linear graft copolymer versus cyclic graft copolymer) can dramatically influence a polymer’s nanostructure and its properties. / Royal Society (Great Britain), Engineering and Physical Sciences Research Council (EPSRC), European Research Council (ERC)

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Die Fortschritte bei synthetischen Polymeren konzentrieren sich in erster Linie auf die Bemühungen, Kunststoffe auf molekularer Ebene zu entwickeln, um vielversprechende Eigenschaften und Funktionen auf makroskopischer Ebene zu erreichen. Daher sind die Verbesserung der Materialsynthese sowie die Zunahme der Komplexität des makromolekularen Designs zu einem wichtigen Forschungsschwerpunkt geworden. Es wurden bemerkenswerte synthetische Strategien zur Entwicklung von sequenzgesteuerten Oligomeren entwickelt, die durch eine präzise Mikrostruktur eine anschließende Faltung zu kontrollierten multizyklischen Origamis ermöglichten. Allerdings bleiben die derzeitigen synthetischen Methoden für die Herstellung von Präzisionspolymeren mit hohem Molekulargewicht bis zu einem gewissen Grad statistisch. Daher ist es nach wie vor schwierig, große synthetische Makromoleküle zu entwerfen, die sich zu präzisen und einheitlichen zyklischen Strukturen zusammenfügen können. Sind parallele Fortschritte bei der Charakterisierung von großen multizyklischen makromolekularen Strukturen sehr gefragt, da die meisten der derzeitigen Techniken nur in der Lage sind, Indizien für die Strukturorganisation zu liefern. Die vorliegende Arbeit untersucht dabei die Synthese und die Morphologie von dynamischen und kontrollierten zyklischen Polymeren. Das synthetische Konzept basiert auf der Herstellung von sequenzgesteuerten Makromolekülen mittels regulierten Einbaus von reaktiven Selenol- oder Thiolgruppen an gewünschten Positionen innerhalb einer Polymerkette. Die kontrollierte oxidative Dimerisierung der funktionellen Gruppen führt zu Diselenid- bzw. Disulfidbrücken und bewirkt eine intramolekulare Vernetzung zur Erzeugung einer dynamischen einkettigen Zyklisierung. Um Einblicke auf molekularer Ebene zu gewinnen und den Grad an struktureller Kontrolle aufzuzeigen, wird eine synthetische Strategie entwickelt, die eine direkte Visualisierung der erhaltenen Polymerkonformation ermöglicht. / The field of material science has evolved drastically in the last decades. Progress in synthetic polymers primarily focuses on efforts to design materials at a molecular level to reach promising properties and functions. Improving material synthesis and increasing the complexity of macromolecular design have become a major research focus. Remarkable synthetic strategies have been developed toward the elaboration of sequence-defined oligomers, in which the precise microstructure can allow subsequent folding into controlled and precise multi-cyclic origamis. However, current synthetic routes toward precision polymers with high molecular weight remain statistical to some degree, which reflects a loss of structural control. Thus, designing large synthetic macromolecules that can fold into precise and uniform cyclic-shape structures remains difficult to reach. Parallel progress in characterization of large multi-cyclic macromolecular designs are highly demanded since most of the current techniques are only capable of providing circumstantial evidence of structural organization. Macromolecules with dynamic intramolecular crosslinks have become relevant due to their ability to potentially reach equilibrium structures in response to external stimuli. In this study, controlled synthetic route and morphology characterization of dynamic cyclic polymers are investigated. The synthetic concept is based on the preparation of sequence-controlled macromolecules to guide the insertion of reactive selenol or thiol groups at desired positions within a polymer chain. Controlled oxidative dimerization of the functional groups leads to diselenide or disulfide bridges respectively and induces intramolecular crosslinking to generate dynamic cyclization. To gain insight into the molecular level to reveal the degree of structural control, a synthetic strategy is developed to access an additional analytic tool and enable direct visualization of the obtained polymer conformations.

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