@phdthesis{Bastian2022,
  author    = {Bastian, Philipp U.},
  title     = {Core-shell upconversion nanoparticles - investigation of dopant intermixing and surface modification},
  doi       = {10.25932/publishup-55160},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-551607},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 108, xxiii},
  year      = {2022},
  abstract  = {Frequency upconversion nanoparticles (UCNPs) are inorganic nanocrystals capable to up-convert incident photons of the near-infrared electromagnetic spectrum (NIR) into higher energy photons. These photons are re-emitted in the range of the visible (Vis) and even ultraviolet (UV) light. The frequency upconversion process (UC) is realized with nanocrystals doped with trivalent lanthanoid ions (Ln(III)). The Ln(III) ions provide the electronic (excited) states forming a ladder-like electronic structure for the Ln(III) electrons in the nanocrystals. The absorption of at least two low energy photons by the nanoparticle and the subsequent energy transfer to one Ln(III) ion leads to the promotion of one Ln(III) electron into higher excited electronic states. One high energy photon will be emitted during the radiative relaxation of the electron in the excited state back into the electronic ground state of the Ln(III) ion. The excited state electron is the result of the previous absorption of at least two low energy photons. The UC process is very interesting in the biological/medical context. Biological samples (like organic tissue, blood, urine, and stool) absorb high-energy photons (UV and blue light) more strongly than low-energy photons (red and NIR light). Thanks to a naturally occurring optical window, NIR light can penetrate deeper than UV light into biological samples. Hence, UCNPs in bio-samples can be excited by NIR light. This possibility opens a pathway for in vitro as well as in vivo applications, like optical imaging by cell labeling or staining of specific organic tissue. Furthermore, early detection and diagnosis of diseases by predictive and diagnostic biomarkers can be realized with bio-recognition elements being labeled to the UCNPs. Additionally, "theranostic" becomes possible, in which the identification and the treatment of a disease are tackled simultaneously. For this to succeed, certain parameters for the UCNPs must be met: high upconversion efficiency, high photoluminescence quantum yield, dispersibility, and dispersion stability in aqueous media, as well as availability of functional groups to introduce fast and easy bio-recognition elements. The UCNPs used in this work were prepared with a solvothermal decomposition synthesis yielding in particles with NaYF4 or NaGdF4 as host lattice. They have been doped with the Ln(III) ions Yb3+ and Er3+, which is only one possible upconversion pair. Their upconversion efficiency and photoluminescence quantum yield were improved by adding a passivating shell to reduce surface quenching. However, the brightness of core-shell UCNPs stays behind the expectations compared to their bulk material (being at least μm-sized particles). The core-shell structures are not clearly separated from each other, which is a topic in literature. Instead, there is a transition layer between the core and the shell structure, which relates to the migration of the dopants within the host lattice during the synthesis. The ion migration has been examined by time-resolved laser spectroscopy and the interlanthanoid resonance energy transfer (LRET) in the two different host lattices from above. The results are presented in two publications, which dealt with core-shell-shell structured nanoparticles. The core is doped with the LRET-acceptor (either Nd3+ or Pr3+). The intermediate shell serves as an insulation shell of pure host lattice material, whose shell thickness has been varied within one set of samples having the same composition, so that the spatial separation of LRET-acceptor and -donor changes. The outer shell with the same host lattice is doped with the LRET-donor (Eu3+). The effect of the increasing insulation shell thickness is significant, although the LRET cannot be suppressed completely. Next to the Ln(III) migration within a host lattice, various phase transfer reactions were investigated in order to subsequently perform surface modifications for bioapplications. One result out of this research has been published using a promising ligand, that equips the UCNP with bio-modifiable groups and has good potential for bio-medical applications. This particular ligand mimics natural occurring mechanisms of mussel protein adhesion and of blood coagulation, which is why the UCNPs are encapsulated very effectively. At the same time, bio-functional groups are introduced. In a proof-of-concept, the encapsulated UCNP has been coupled successfully with a dye (which is representative for a biomarker) and the system's photoluminescence properties have been investigated.},
  language  = {en}
}
@phdthesis{Brandi2022,
  author    = {Brandi, Francesco},
  title     = {Integrated biorefinery in continuous flow systems using sustainable heterogeneous catalysts},
  doi       = {10.25932/publishup-53766},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-537660},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 201},
  year      = {2022},
  abstract  = {The negative impact of crude oil on the environment has led to a necessary transition toward alternative, renewable, and sustainable resources. In this regard, lignocellulosic biomass (LCB) is a promising renewable and sustainable alternative to crude oil for the production of fine chemicals and fuels in a so-called biorefinery process. LCB is composed of polysaccharides (cellulose and hemicellulose), as well as aromatics (lignin). The development of a sustainable and economically advantageous biorefinery depends on the complete and efficient valorization of all components. Therefore, in the new generation of biorefinery, the so-called biorefinery of type III, the LCB feedstocks are selectively deconstructed and catalytically transformed into platform chemicals. For this purpose, the development of highly stable and efficient catalysts is crucial for progress toward viability in biorefinery. Furthermore, a modern and integrated biorefinery relies on process and reactor design, toward more efficient and cost-effective methodologies that minimize waste. In this context, the usage of continuous flow systems has the potential to provide safe, sustainable, and innovative transformations with simple process integration and scalability for biorefinery schemes. This thesis addresses three main challenges for future biorefinery: catalyst synthesis, waste feedstock valorization, and usage of continuous flow technology. Firstly, a cheap, scalable, and sustainable approach is presented for the synthesis of an efficient and stable 35 wt.-\% Ni catalyst on highly porous nitrogen-doped carbon support (35Ni/NDC) in pellet shape. Initially, the performance of this catalyst was evaluated for the aqueous phase hydrogenation of LCB-derived compounds such as glucose, xylose, and vanillin in continuous flow systems. The 35Ni/NDC catalyst exhibited high catalytic performances in three tested hydrogenation reactions, i.e., sorbitol, xylitol, and 2-methoxy-4-methylphenol with yields of 82 mol\%, 62 mol\%, and 100 mol\% respectively. In addition, the 35Ni/NDC catalyst exhibited remarkable stability over a long time on stream in continuous flow (40 h). Furthermore, the 35Ni/NDC catalyst was combined with commercially available Beta zeolite in a dual-column integrated process for isosorbide production from glucose (yield 83 mol\%). Finally, 35Ni/NDC was applied for the valorization of industrial waste products, namely sodium lignosulfonate (LS) and beech wood sawdust (BWS) in continuous flow systems. The LS depolymerization was conducted combining solvothermal fragmentation of water/alcohol mixtures (i.e.,methanol/water and ethanol/water) with catalytic hydrogenolysis/hydrogenation (SHF). The depolymerization was found to occur thermally in absence of catalyst with a tunable molecular weight according to temperature. Furthermore, the SHF generated an optimized cumulative yield of lignin-derived phenolic monomers of 42 mg gLS-1. Similarly, a solvothermal and reductive catalytic fragmentation (SF-RCF) of BWS was conducted using MeOH and MeTHF as a solvent. In this case, the optimized total lignin-derived phenolic monomers yield was found of 247 mg gKL-1.},
  language  = {en}
}
@phdthesis{Brinkmann2022,
  author    = {Brinkmann, Pia},
  title     = {Laserinduzierte Breakdownspektroskopie zur qualitativen und quantitativen Bestimmung von Elementgehalten in geologischen Proben mittels multivariater Analysemethoden am Beispiel von Kupfer und ausgew{\"a}hlten Seltenen Erden},
  doi       = {10.25932/publishup-57212},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-572128},
  school      = {Universit{\"a}t Potsdam},
  pages     = {148},
  year      = {2022},
  abstract  = {Ein schonender Umgang mit den Ressourcen und der Umwelt ist wesentlicher Bestandteil des modernen Bergbaus sowie der zuk{\"u}nftigen Versorgung unserer Gesellschaft mit essentiellen Rohstoffen. Die vorliegende Arbeit besch{\"a}ftigt sich mit der Entwicklung analytischer Strategien, die durch eine exakte und schnelle Vor-Ort-Analyse den technisch-praktischen Anforderungen des Bergbauprozesses gerecht werden und somit zu einer gezielten und nachhaltigen Nutzung von Rohstofflagerst{\"a}tten beitragen. Die Analysen basieren auf den spektroskopischen Daten, die mittels der laserinduzierten Breakdownspektroskopie (LIBS) erhalten und mittels multivariater Datenanalyse ausgewertet werden. Die LIB-Spektroskopie ist eine vielversprechende Technik f{\"u}r diese Aufgabe. Ihre Attraktivit{\"a}t machen insbesondere die M{\"o}glichkeiten aus, Feldproben vor Ort ohne Probennahme oder ‑vorbereitung messen zu k{\"o}nnen, aber auch die Detektierbarkeit s{\"a}mtlicher Elemente des Periodensystems und die Unabh{\"a}ngigkeit vom Aggregatzustand. In Kombination mit multivariater Datenanalyse kann eine schnelle Datenverarbeitung erfolgen, die Aussagen zur qualitativen Elementzusammensetzung der untersuchten Proben erlaubt. Mit dem Ziel die Verteilung der Elementgehalte in einer Lagerst{\"a}tte zu ermitteln, werden in dieser Arbeit Kalibrierungs- und Quantifizierungsstrategien evaluiert. F{\"u}r die Charakterisierung von Matrixeffekten und zur Klassifizierung von Mineralen werden explorative Datenanalysemethoden angewendet. Die spektroskopischen Untersuchungen erfolgen an B{\"o}den und Gesteinen sowie an Mineralen, die Kupfer oder Seltene Erdelemente beinhalten und aus verschiedenen Lagerst{\"a}tten bzw. von unterschiedlichen Agrarfl{\"a}chen stammen. F{\"u}r die Entwicklung einer Kalibrierungsstrategie wurden sowohl synthetische als auch Feldproben von zwei verschiedenen Agrarfl{\"a}chen mittels LIBS analysiert. Anhand der Beispielanalyten Calcium, Eisen und Magnesium erfolgte die auf uni- und multivariaten Methoden beruhende Evaluierung verschiedener Kalibrierungsmethoden. Grundlagen der Quantifizierungsstrategien sind die multivariaten Analysemethoden der partiellen Regression der kleinsten Quadrate (PLSR, von engl.: partial least squares regression) und der Intervall PLSR (iPLSR, von engl.: interval PLSR), die das gesamte detektierte Spektrum oder Teilspektren in der Analyse ber{\"u}cksichtigen. Der Untersuchung liegen synthetische sowie Feldproben von Kupfermineralen zugrunde als auch solche die Seltene Erdelemente beinhalten. Die Proben stammen aus verschiedenen Lagerst{\"a}tten und weisen unterschiedliche Begleitmatrices auf. Mittels der explorativen Datenanalyse erfolgte die Charakterisierung dieser Begleitmatrices. Die daf{\"u}r angewendete Hauptkomponentenanalyse gruppiert Daten anhand von Unterschieden und Regelm{\"a}ßigkeiten. Dies erlaubt Aussagen {\"u}ber Gemeinsamkeiten und Unterschiede der untersuchten Proben im Bezug auf ihre Herkunft, chemische Zusammensetzung oder lokal bedingte Auspr{\"a}gungen. Abschließend erfolgte die Klassifizierung kupferhaltiger Minerale auf Basis der nicht-negativen Tensorfaktorisierung. Diese Methode wurde mit dem Ziel verwendet, unbekannte Proben aufgrund ihrer Eigenschaften in Klassen einzuteilen. Die Verkn{\"u}pfung von LIBS und multivariater Datenanalyse bietet die M{\"o}glichkeit durch eine Analyse vor Ort auf eine Probennahme und die entsprechende Laboranalytik weitestgehend zu verzichten und kann somit zum Umweltschutz sowie einer Schonung der nat{\"u}rlichen Ressourcen bei der Prospektion und Exploration von neuen Erzg{\"a}ngen und Lagerst{\"a}tten beitragen. Die Verteilung von Elementgehalten der untersuchten Gebiete erm{\"o}glicht zudem einen gezielten Abbau und damit eine effiziente Nutzung der mineralischen Rohstoffe.},
  language  = {de}
}
@phdthesis{Baeckemo2022,
  author    = {B{\"a}ckemo, Johan Dag Valentin},
  title     = {Digital tools and bioinspiration for the implementation in science and medicine},
  doi       = {10.25932/publishup-57145},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-571458},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiv, 108},
  year      = {2022},
  abstract  = {Diese Doktorarbeit untersucht anhand dreier Beispiele, wie digitale Werkzeuge wie Programmierung, Modellierung, 3D-Konstruktions-Werkzeuge und additive Fertigung in Verbindung mit einer auf Biomimetik basierenden Design\-strategie zu neuen Analysemethoden und Produkten f{\"u}hren k{\"o}nnen, die in Wissenschaft und Medizin Anwendung finden. Das Verfahren der Funkenerosion (EDM) wird h{\"a}ufig angewandt, um harte Metalle zu verformen oder zu formen, die mit normalen Maschinen nur schwer zu bearbeiten sind. In dieser Arbeit wird eine neuartige Kr{\"u}mmungsanalysemethode als Alternative zur Rauheitsanalyse vorgestellt. Um besser zu verstehen, wie sich die Oberfl{\"a}che w{\"a}hrend der Bearbeitungszeit des EDM-Prozesses ver{\"a}ndert, wurde außerdem ein digitales Schlagmodell erstellt, das auf einem urspr{\"u}nglich flachen Substrat Krater auf Erhebungen erzeugte. Es wurde festgestellt, dass ein Substrat bei etwa 10.000 St{\"o}ßen ein Gleichgewicht erreicht. Die vorgeschlagene Kr{\"u}mmungsanalysemethode hat das Potenzial, bei der Entwicklung neuer Zellkultursubstrate f{\"u}r die Stammzellenforschung eingesetzt zu werden. Zwei Arten, die in dieser Arbeit aufgrund ihrer interessanten Mechanismen analysiert wurden, sind die Venusfliegenfalle und der Bandwurm. Die Venusfliegenfalle kann ihr Maul mit einer erstaunlichen Geschwindigkeit schließen. Der Schließmechanismus kann f{\"u}r die Wissenschaft interessant sein und ist ein Beispiel f{\"u}r ein so genanntes mechanisch bi-stabiles System - es gibt zwei stabile Zust{\"a}nde. Der Bandwurm ist bei S{\"a}ugetieren meist im unteren Darm zu finden und heftet sich mit seinen Saugn{\"a}pfen an die Darmw{\"a}nde. Wenn der Bandwurm eine geeignete Stelle gefunden hat, st{\"o}ßt er seine Haken aus und heftet sich dauerhaft an die Wand. Diese Funktion k{\"o}nnte in der minimalinvasiven Medizin genutzt werden, um eine bessere Kontrolle der Implantate w{\"a}hrend des Implantationsprozesses zu erm{\"o}glichen. F{\"u}r beide Projekte wurde ein mathematisches Modell, das so genannte Chained Beam Constraint Model (CBCM), verwendet, um das nichtlineare Biegeverhalten zu modellieren und somit vorherzusagen, welche Strukturen ein mechanisch bi-stabiles Verhalten aufweisen k{\"o}nnten. Daraufhin konnten zwei Prototypen mit einem 3D-Drucker gedruckt und durch Experimente veranschaulicht werden, dass sie beide ein bi-stabiles Verhalten aufweisen. Diese Arbeit verdeutlicht das hohe Anwendungspotenzial f{\"u}r neue Analysenmethoden in der Wissenschaft und f{\"u}r neue Medizinprodukte in der minimalinvasiven Medizin.},
  language  = {en}
}
@phdthesis{Chea2022,
  author    = {Chea, Sany},
  title     = {Glycomaterials: From synthesis of glycoconjugates to potential biomedical applications},
  doi       = {10.25932/publishup-57424},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-574240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVII, 217},
  year      = {2022},
  abstract  = {The importance of carbohydrate structures is enormous due to their ubiquitousness in our lives. The development of so-called glycomaterials is the result of this tremendous significance. These are not exclusively used for research into fundamental biological processes, but also, among other things, as inhibitors of pathogens or as drug delivery systems. This work describes the development of glycomaterials involving the synthesis of glycoderivatives, -monomers and -polymers. Glycosylamines were synthesized as precursors in a single synthesis step under microwave irradiation to significantly shorten the usual reaction time. Derivatization at the anomeric position was carried out according to the methods developed by Kochetkov and Likhorshetov, which do not require the introduction of protecting groups. Aminated saccharide structures formed the basis for the synthesis of glycomonomers in β-configuration by methacrylation. In order to obtain α-Man-based monomers for interactions with certain α-Man-binding lectins, a monomer synthesis by Staudinger ligation was developed in this work, which also does not require protective groups. Modification of the primary hydroxyl group of a saccharide was accomplished by enzyme-catalyzed synthesis. Ribose-containing cytidine was transesterified using the lipase Novozym 435 and microwave irradiation. The resulting monomer synthesis was optimized by varying the reaction partners. To create an amide bond instead of an ester bond, protected cytidine was modified by oxidation followed by amide coupling to form the monomer. This synthetic route was also used to isolate the monomer from its counterpart guanosine. After obtaining the nucleoside-based monomers, they were block copolymerized using the RAFT method. Pre-synthesized pHPMA served as macroCTA to yield cytidine- or guanosine-containing block copolymer. These isolated block copolymers were then investigated for their self-assembly behavior using UV-Vis, DLS and SEM to serve as a potential thermoresponsive drug delivery system.},
  language  = {en}
}
@phdthesis{Doering2022,
  author    = {Doering, Ulrike},
  title     = {Preparation, characterization and modification of oil loaded protein microcapsules and composite protein-mineral microcapsules},
  doi       = {10.25932/publishup-55958},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-559589},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 115},
  year      = {2022},
  abstract  = {Diese Doktorarbeit behandelt die Synthese von Protein- und kompositen Protein-Mineral-Mikrokapseln durch die Anwendung von hochintensivem Ultraschall an der {\"O}l-Wasser-Grenzfl{\"a}che. W{\"a}hrend ein System durch BSA-Molek{\"u}le stabilisiert wird, wird das andere System durch verschiedene mit BSA modifizierten Nanopartikeln stabilisiert. Sowohl von allen Synthesestufen als auch von den resultierenden Kapseln wurden umfassende Untersuchungen durchgef{\"u}hrt und eine plausible Erkl{\"a}rung f{\"u}r den Mechanismus der Kapselbildung wurde vorgestellt. W{\"a}hrend der Bildung der BSA-Mikrokapseln adsorbieren die Proteinmolek{\"u}le als Erstes an der O/W-Grenzfl{\"a}che, entfalten sich dort und bilden ein Netzwerk, das durch hydrophobe Wechselwirkungen und Wasserstoffbr{\"u}ckenbindungen zwischen den benachbarten Molek{\"u}len stabilisiert wird. Gleichzeitig bewirkt die Ultraschallbehandlung die Quervernetzung der BSA-Molek{\"u}le {\"u}ber die Bildung von intermolekularen Disulfidbindungen. In dieser Doktorarbeit werden die experimentellen Nachweise f{\"u}r die durch Ultraschall induzierte Quervernetzung von BSA in den Schalen der proteinbasierten Mikrokapseln aufgezeigt. Deshalb wurde das Konzept, das vor vielen Jahren von Suslick und seinen Mitarbeitern vorgestellt wurde, zum ersten Mal durch experimentelle Nachweise best{\"a}tigt. Außerdem wurde ein konsistenter Mechanismus f{\"u}r die Bildung der intermolekularen Disulfidbindungen in der Kapselschale vorgestellt, der auf der Neuverteilung der Thiol- und Disulfidgruppen in BSA unter der Wirkung von hochenergetischem Ultraschall basiert. Auch die Bildung von kompositen Protein-Mineral-Mikrokapseln, die mit drei verschiedenen {\"O}len gef{\"u}llt wurden und deren Schalen aus Nanopartikeln bestehen, war erfolgreich. Die Beschaffenheit des {\"O}ls und die Art der Nanopartikel in der Schale hatten Einfluss auf die Gr{\"o}ße und Form der Mikrokapseln. Die Untersuchung der kompositen Kapseln zeigte, dass die BSA-Molek{\"u}le, die an der Oberfl{\"a}che der Nanopartikel in der Kapselschale adsorbiert sind, nicht durch intermolekulare Disulfidbindungen quervernetzt sind. Stattdessen findet die Bildung einer Pickering-Emulsion statt. Die Oberfl{\"a}chenmodifizierung der kompositen Mikrokapseln durch Vormodifizierung der Hauptbestandteile und auch durch Postmodifizierung der Oberfl{\"a}che der fertigen kompositen Mikrokapseln wurde erfolgreich demonstriert. Zus{\"a}tzlich wurden die mechanischen Eigenschaften beider Kapselarten verglichen. Dabei erwiesen sich die Protein-Mikrokapseln widerstandsf{\"a}higer gegen{\"u}ber elastischer Deformation.},
  language  = {en}
}
@phdthesis{Fischer2022,
  author    = {Fischer, Eric Wolfgang},
  title     = {Quantum vibrational dynamics in complex environments: from vibrational strong coupling in molecular cavity QED to phonon-induced adsorbate relaxation},
  doi       = {10.25932/publishup-56721},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-567214},
  school      = {Universit{\"a}t Potsdam},
  pages     = {viii, 171},
  year      = {2022},
  abstract  = {Molecules are often naturally embedded in a complex environment. As a consequence, characteristic properties of a molecular subsystem can be substantially altered or new properties emerge due to interactions between molecular and environmental degrees of freedom. The present thesis is concerned with the numerical study of quantum dynamical and stationary properties of molecular vibrational systems embedded in selected complex environments. In the first part, we discuss "strong-coupling" model scenarios for molecular vibrations interacting with few quantized electromagnetic field modes of an optical Fabry-P{\´e}rot cavity. We thoroughly elaborate on properties of emerging "vibrational polariton" light-matter hybrid states and examine the relevance of the dipole self-energy. Further, we identify cavity-induced quantum effects and an emergent dynamical resonance in a cavity-altered thermal isomerization model, which lead to significant suppression of thermal reaction rates. Moreover, for a single rovibrating diatomic molecule in an optical cavity, we observe non-adiabatic signatures in dynamics due to "vibro-polaritonic conical intersections" and discuss spectroscopically accessible "rovibro-polaritonic" light-matter hybrid states. In the second part, we study a weakly coupled but numerically challenging quantum mechanical adsorbate-surface model system comprising a few thousand surface modes. We introduce an efficient construction scheme for a "hierarchical effective mode" approach to reduce the number of surface modes in a controlled manner. In combination with the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method, we examine the vibrational adsorbate relaxation dynamics from different excited adsorbate states by solving the full non-Markovian system-bath dynamics for the characteristic relaxation time scale. We examine half-lifetime scaling laws from vibrational populations and identify prominent non-Markovian signatures as deviations from Markovian reduced system density matrix theory in vibrational coherences, system-bath entanglement and energy transfer dynamics. In the final part of this thesis, we approach the dynamics and spectroscopy of vibronic model systems at finite temperature by formulating the ML-MCTDH method in the non-stochastic framework of thermofield dynamics. We apply our method to thermally-altered ultrafast internal conversion in the well-known vibronic coupling model of pyrazine. Numerically beneficial representations of multilayer wave functions ("ML-trees") are identified for different temperature regimes, which allow us to access thermal effects on both electronic and vibrational dynamics as well as spectroscopic properties for several pyrazine models.},
  language  = {en}
}
@phdthesis{Flatken2022,
  author    = {Flatken, Marion A.},
  title     = {The early stages of halide perovskites thin film formation},
  doi       = {10.25932/publishup-55259},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-552599},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 144},
  year      = {2022},
  abstract  = {As climate change worsens, there is a growing urgency to promote renewable energies and improve their accessibility to society. Here, solar energy harvesting is of particular importance. Currently, metal halide perovskite (MHP) solar cells are indispensable in future solar energy generation research. MHPs are crystalline semiconductors increasingly relevant as low-cost, high-performance materials for optoelectronics. Their processing from solution at low temperature enables easy fabrication of thin film elements, encompassing solar cells and light-emitting diodes or photodetectors. Understanding the coordination chemistry of MHPs in their precursor solution would allow control over the thin film crystallization, the material properties and the final device performance. In this work, we elaborate on the key parameters to manipulate the precursor solution with the long-term objective of enabling systematic process control. We focus on the nanostructural characterization of the initial arrangements of MHPs in the precursor solutions. Small-angle scattering is particularly well suited for measuring nanoparticles in solution. This technique proved to be valuable for the direct analyzes of perovskite precursor solutions in standard processing concentrations without causing radiation damage. We gain insights into the chemical nature of widely used precursor structures such as methylammonium lead iodide (MAPbI3), presenting first insights into the complex arrangements and interaction within this precursor state. Furthermore, we transfer the preceding results to other more complex perovskite precursors. The influence of compositional engineering is investigated using the addition of alkali cations as an example. As a result, we propose a detailed working mechanism on how the alkali cations suppress the formation of intermediate phases and improve the quality of the crystalline thin film. In addition, we investigate the crystallization process of a tin-based perovskite composition (FASnI3) under the influence of fluoride chemistry. We prove that the frequently used additive, tin fluoride (SnF2), selectively binds undesired oxidized tin (Sn(IV)) in the precursor solution. This prevents its incorporation into the actual crystal structure and thus reduces the defect density of the material. Furthermore, SnF2 leads to a more homogeneous crystal growth process, which results in improved crystal quality of the thin film material. In total, this study provides a detailed characterization of the complex system of perovskite precursor chemistry. We thereby cover relevant parameters for future MHP solar cell process control, such as (I) the environmental impact based on concentration and temperature (II) the addition of counter ions to reduce the diffuse layer surrounding the precursor nanostructures and (III) the targeted use of additives to eliminate unwanted components selectively and to ensure a more homogeneous crystal growth.},
  language  = {en}
}
@phdthesis{Freyse2022,
  author    = {Freyse, Daniel},
  title     = {Thioacetal-Bausteine f{\"u}r Fluoreszenzfarbstoffe und molekulare St{\"a}be},
  doi       = {10.25932/publishup-54925},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549252},
  school      = {Universit{\"a}t Potsdam},
  pages     = {292},
  year      = {2022},
  abstract  = {Im Rahmen dieser Dissertation wurde der Sauerstoff im Grundger{\"u}st der [1,3]-Dioxolo[4.5-f]benzodioxol-Fluoreszenzfarbstoffe (DBD-Fluoreszenzfarbstoffe) vollst{\"a}ndig mit Schwefel ausgetauscht und daraus eine neue Klasse von Fluoreszenzfarbstoffen entwickelt, die Benzo[1,2-d:4,5-d']bis([1,3]dithiol)-Fluorophore (S4-DBD-Fluorophore). Insgesamt neun der besonders interessanten, difunktionalisierten Vertreter konnten synthetisiert werden, die sich in ihren elektronenziehenden Gruppen und in ihrer Anordnung unterschieden. Durch den Austausch von Sauerstoff mit Schwefel kam es zu teilweise auff{\"a}lligen Ver{\"a}nderungen in den Fluoreszenzparametern, wie eine Abnahme der Fluoreszenzquantenausbeuten und -lebenszeiten aber auch eine deutliche Rotverschiebung in den Absorptions- und Emissionswellenl{\"a}ngen mit großen STOKES-Verschiebungen. Damit sind die S4-DBD-Fluorophore eine wertvolle Erg{\"a}nzung f{\"u}r die DBD-Farbstoffe. Die Ursachen f{\"u}r die Abnahme der Lebenszeiten und Quantenausbeuten konnte auf eine hohe Besetzung des Triplett-Zustandes zur{\"u}ckgef{\"u}hrt werden, welcher durch die verst{\"a}rkten Spin-Bahn-Kopplungen des Schwefels hervorgerufen wird. Zusammen mit dem Arbeitskreis physikalische Chemie der Universit{\"a}t Potsdam konnten auch die photophysikalischen Prozesse {\"u}ber die Transienten-Absorptionsspektroskopie (TAS) aufgekl{\"a}rt werden. Eine Strategie zur Funktionalisierung der S4-DBD-Farbstoffe am Thioacetalger{\"u}st konnte entwickelt werden. So gelang es Alkohol-, Propargyl-, Azid-, NHS-Ester-, Carbons{\"a}ure-, Maleimid- und Tosyl-Gruppen an S4-DBD-Dialdehyden anzubringen. Erweiternd wurden molekulare St{\"a}be auf Basis von Schwefel-Oligo-Spiro-Ketalen (SOSKs) untersucht, bei denen Sauerstoff durch Schwefel ersetzt wurde. Hier konnten die Synthesen der l{\"o}slichkeitsvermittelnden TER-Muffe und auch des Tetrathiapentaerythritols als Grundbaustein deutlich verbessert werden. Aus diesen konnte ein einfaches SOSK-Polymer hergestellt werden. Weitere Versuche zum Aufbau eines Stabes m{\"u}ssen aber noch untersucht werden. Um einen S-OSK-Stab aufzubauen hat sich dabei die Dithiocarbonat-Gruppe in ersten Versuchen als potenzielle geeignete Schutzgruppe f{\"u}r das Tetrathiapentaerythritol herausgestellt.},
  language  = {de}
}
@phdthesis{Gaebert2022,
  author    = {G{\"a}bert, Chris},
  title     = {Light-responsive polymer systems aiming towards programmable friction},
  doi       = {10.25932/publishup-55338},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-553380},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVI, 108, XXVI},
  year      = {2022},
  abstract  = {The development of novel programmable materials aiming to control friction in real-time holds potential to facilitate innovative lubrication solutions for reducing wear and energy losses. This work describes the integration of light-responsiveness into two lubricating materials, silicon oils and polymer brush surfaces. The first part focusses on the assessment on 9-anthracene ester-terminated polydimethylsiloxanes (PDMS-A) and, in particular, on the variability of rheological properties and the implications that arise with UV-light as external trigger. The applied rheometer setup contains an UV-transparent quartz-plate, which enables radiation and simultaneous measurement of the dynamic moduli. UV-A radiation (354 nm) triggers the cycloaddition reaction between the terminal functionalities of linear PDMS, resulting in chain extension. The newly-formed anthracene dimers cleave by UV-C radiation (254 nm) or at elevated temperatures (T > 130 °C). The sequential UV-A radiation and thermal reprogramming over three cycles demonstrate high conversions and reproducible programming of rheological properties. In contrast, the photochemical back reaction by UV-C is incomplete and can only partially restore the initial rheological properties. The dynamic moduli increase with each cycle in photochemical programming, presumably resulting from a chain segment re-arrangement as a result of the repeated partial photocleavage and subsequent chain length-dependent dimerization. In addition, long periods of radiation cause photooxidative degradation, which damages photo-responsive functions and consequently reduces the programming range. The absence of oxygen, however, reduces undesired side reactions. Anthracene-functionalized PDMS and native PDMS mix depending on the anthracene ester content and chain length, respectively, and allow fine-tuning of programmable rheological properties. The work shows the influence of mixing conditions during the photoprogramming step on the rheological properties, indicating that material property gradients induced by light attenuation along the beam have to be considered. Accordingly, thin lubricant films are suggested as potential application for light-programmable silicon fluids. The second part compares strategies for the grafting of spiropyran (SP) containing copolymer brushes from Si wafers and evaluates the light-responsiveness of the surfaces. Pre-experiments on the kinetics of the thermally initiated RAFT copolymerization of 2-hydroxyethyl acrylate (HEA) and spiropyran acrylate (SPA) in solution show, first, a strong retardation by SP and, second, the dependence of SPA polymerization on light. Surprisingly, the copolymerization of SPA is inhibited in the dark. These findings contribute to improve the synthesis of polar, spiropyran-containing copolymers. The comparison between initiator systems for the grafting-from approach indicates PET-RAFT superior to thermally initiated RAFT, suggesting a more efficient initiation of surface-bound CTA by light. Surface-initiated polymerization via PET-RAFT with an initiator system of EosinY (EoY) and ascorbic acid (AscA) facilitates copolymer synthesis from HEA and 5-25 mol\% SPA. The resulting polymer film with a thickness of a few nanometers was detected by atomic force microscopy (AFM) and ellipsometry. Water contact angle (CA) measurements demonstrate photo-switchable surface polarity, which is attributed to the photoisomerization between non-polar spiropyran and zwitterionic merocyanine isomer. Furthermore, the obtained spiropyran brushes show potential for further studies on light-programmable properties. In this context, it would be interesting to investigate whether swollen spiropyran-containing polymers change their configuration and thus their film thickness under the influence of light. In addition, further experiments using an AFM or microtribometer should evaluate whether light-programmable solvation enables a change in frictional properties between polymer brush surfaces.},
  language  = {en}
}