@phdthesis{Arya2020,
  author    = {Arya, Pooja},
  title     = {Light controlled active and passive motion of colloidal particles},
  doi       = {10.25932/publishup-48388},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483880},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 183},
  year      = {2020},
  abstract  = {In this dissertation we introduce a concept of light driven active and passive manipulation of colloids trapped at solid/liquid interface. The motion is induced due to generation of light driven diffusioosmotic flow (LDDO) upon irradiation with light of appropriate wavelength. The origin of the flow is due to osmotic pressure gradient resulting from a concentration gradient at the solid/liquid interface of the photosensitive surfactant present in colloidal dispersion. The photosensitive surfactant consists of a cationic head group and a hydrophobic tail in which azobenzene group is integrated in. The azobenzene is known to undergo reversible photo-isomerization from a stable trans to a meta stable cis state under irradiation with UV light. Exposure to light of larger wavelength results in back photo-isomerization from cis to trans state. The two isomers have different molecular properties, for instance, trans isomer has a rod like structure and low polarity (0 dipole moment), whereas cis one is bent and has a dipole moment of ~3 Debye. Being integrated in the hydrophobic tail of the surfactant molecule, the azobenzene state determines the hydrophobicity of the whole molecule: in the trans state the surfactant is more hydrophobic than in the cis-state. In this way many properties of the surfactant such as the CMC, solubility and the interaction potential with a solid surface can be altered by light. When the solution containing such a surfactant is irradiated with focused light, a concentration gradient of different isomers is formed near the boundary of the irradiated area near the solid surface resulting in osmotic pressure gradient. The generated diffusioosmotic (DO) flow carries the particles passively along. The local-LDDO flow can be generated around and by each particle when mesoporous silica colloids are dispersed in the surfactant solution. This is because porous particles act as a sink/source which absorbs azobenzene molecule in trans state and expels it when it is in the cis state. The DO flows generated at each particle interact resulting in aggregation or separation depending upon the initial state of surfactant molecules. The kinetic of aggregation and separation can be controlled and manipulated by altering the parameters such as the wavelength and intensity of the applied light, as well as surfactant and particle concentration. Using two wavelengths simultaneously allows for dynamic gathering and separation creating fascinating patterns such as 2D disk of well separated particles or establishing collective complex behaviour of particle ensemble as described in this thesis. The mechanism of l-LDDO is also used to generate self-propelled motion. This is possible when half of the porous particle is covered by metal layer, basically blocking the pores on one side. The LDDO flow generated on uncapped side pushes the particle forward resulting in a super diffusive motion. The system of porous particle and azobenzene containing surfactant molecule can be utilized for various application such as drug delivery, cargo transportation, self-assembling, micro motors/ machines or micro patterning.},
  language  = {en}
}
@phdthesis{Czarnecki2021,
  author    = {Czarnecki, Maciej},
  title     = {Untersuchungen zur Synthese von (1,7)-Naphthalenophanen {\"u}ber eine Dehydro-DIELS-ALDER-Reaktion als Schl{\"u}sselschritt},
  doi       = {10.25932/publishup-50867},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-508670},
  school      = {Universit{\"a}t Potsdam},
  pages     = {vii, 227, XXX},
  year      = {2021},
  abstract  = {Die vorliegende Dissertation behandelt drei thematische Schwerpunkte. Im Ergebnisteil steht die chemische Synthese von sogenannten (1,7)-Naphthalenophanen im Vordergrund, die zur Substanzklasse von Cyclophanen geh{\"o}ren. W{\"a}hrend zahlreiche Synthesemethoden Strategien zum Aufbau von Ringsystemen (wie z. B. von Naphthalenophanen) verfolgen, die Teil einer bereits existierenden aromatischen Struktur der Ausgangsverbindung sind, nutzen nur wenige Ans{\"a}tze Reaktionen, die einen Ringschluss zum gew{\"u}nschten Produkt erst im Zuge der Synthese etablieren. Eine Benzanellierung, die eine besondere Aufmerksamkeit im Arbeitskreis erfahren hat, ist die Dehydro-DIELS-ALDER-Reaktion (DDA-Reaktion). Im Rahmen dieser Arbeit konnte gezeigt werden, dass zw{\"o}lf ausgew{\"a}hlte (1,7)-Naphthalenophane, die teilweise ringgespannt und makrozyklisch aufgebaut waren, mithilfe einer photochemischen Variante der DDA-Reaktion (PDDA-Reaktion) zug{\"a}nglich gemacht werden k{\"o}nnen. Die Versuche, auf thermischem Wege (TDDA-Reaktion) (1,7)-Naphthalenophane herzustellen, misslangen. Die außergew{\"o}hnliche Reaktivit{\"a}t der Photoreaktanten konnte mithilfe quantenchemischer Berechnungen durch eine gefaltete Grundzustandsgeometrie erkl{\"a}rt werden. Dar{\"u}ber hinaus wurden Ringspannungen und strukturelle Spannungsindikatoren der relevanten Photoprodukte ermittelt und Trends in Abh{\"a}ngigkeit der Linkerl{\"a}nge in den NMR-Spektren der Zielverbindungen ermittelt sowie diskutiert. Zudem zeigte eine Variation am Chromophor (Acyl-, Carbons{\"a}ure- und Carbons{\"a}ureester) der Photoreaktanten bei der Bestrahlung in Dichlormethan eine vergleichbare Photokinetik und -reaktivit{\"a}t. Der zweite Abschnitt dieser Dissertation ist dem Design und der Entwicklung zweier Photoreaktoren f{\"u}r UV-Anwendungen im kontinuierlichen Durchfluss gewidmet, da photochemische Transformationen bekanntermaßen in ihrer Skalierbarkeit limitiert sind. Im ersten Prototyp konnten mittels effizienter Parallelschaltung mit bis zu drei UV-Lampen (𝜆𝜆 = 254, 310 und 355 nm) Produktmaterialmengen von bis zu n = 188 mmol anhand eines ausgew{\"a}hlten Fallbeispiels erreicht werden. Im konstruktionstechnisch stark vereinfachten zweiten Photoreaktor wurden alle quarzhaltigen Elemente gegen g{\"u}nstigeres PLEXIGLAS® ersetzt. Das Resultat waren identische Raum-Zeit-Ausbeuten in Bezug auf das zuvor gew{\"a}hlte Synthesebeispiel. Demnach bietet die UV-Photochemie im kontinuierlichen Durchfluss Vorteile gegen{\"u}ber der traditionellen Bestrahlung im Tauchreaktor. Hinsichtlich Reaktionszeit, Produktausbeuten und L{\"o}semittelverbrauch ist sie synthetisch weit {\"u}berlegen. Im letzten Abschnitt der Arbeit wurden diese Erkenntnisse genutzt, um biomedizinisch und pharmakologisch vielversprechende 1-Arylnaphthalen-Lignane mittels einer intramolekularen PDDA-Reaktion (IMPDDA-Reaktion) als Schl{\"u}sselschritt herzustellen. Hierzu wurden drei Konzepte erarbeitet und in der Totalsynthese von drei ausgew{\"a}hlten Zielstrukturen auf Basis des 1-Arylnaphthalengrundger{\"u}sts realisiert.},
  language  = {de}
}
@article{EckertNorellMiedemaetal.2017,
  author    = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and van Kuiken, Benjamin and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander},
  title     = {Untersuchung unabh{\"a}ngiger N-H- und N-C-Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung},
  series = {Angewandte Chemie},
  volume    = {129},
  journal   = {Angewandte Chemie},
  number    = {22},
  issn      = {1521-3757},
  doi       = {10.1002/ange.201700239},
  pages     = {6184 -- 6188},
  year      = {2017},
  abstract  = {Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und R{\"o}ntgenpulsen erm{\"o}glicht eine selektive Verformung von chemischen N-H- und N-C-Bindungen in 2-Thiopyridon in w{\"a}ssriger L{\"o}sung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung an der N1s-Resonanz am Synchrotron und dem Freie-Elektronen-Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molek{\"u}lverformungen und ihrer ultrakurzen Zeitskala.},
  language  = {de}
}
@misc{EckertNorellMiedemaetal.2017,
  author    = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and van Kuiken, Benjamin E. and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander},
  title     = {Untersuchung unabh{\"a}ngiger N-H- und N-C-Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {1121},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-43668},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436688},
  pages     = {7},
  year      = {2017},
  abstract  = {Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und R{\"o}ntgenpulsen erm{\"o}glicht eine selektive Verformung von chemischen N-H- und N-C-Bindungen in 2-Thiopyridon in w{\"a}ssriger L{\"o}sung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung an der N1s-Resonanz am Synchrotron und dem Freie-Elektronen-Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molek{\"u}lverformungen und ihrer ultrakurzen Zeitskala.},
  language  = {de}
}
@phdthesis{Fischer2005,
  author    = {Fischer, Thomas},
  title     = {Lichtinduzierte Orientierungsprozesse in Azobenzen-Polymeren},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7133},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Die Beeinflussung optischer Eigenschaften durch Bestrahlung stellt eine Grundlage f{\"u}r die Herstellung anisotroper optischer Komponenten dar. In d{\"u}nnen Schichten von Azobenzen-Polymeren kann optische Anisotropie durch linear polarisierte Bestrahlung induziert oder modifiziert werden. Ziel der Arbeit war es, wesentliche Struktur-Eigenschafts-Beziehungen zum Prozess der Photoorientierung zu erarbeiten, um so eine Optimierung der Materialien f{\"u}r verschiedene Anwendungen erm{\"o}glichen. In isotropen Schichten fl{\"u}ssigkristalliner und amorpher Azobenzen-Polymeren wird das Ausmaß der induzierten optischen Anisotropie g{\"u}nstig durch eine Donor/Akzeptor-Substitution in 4,4'-Position beeinflusst. Die Induktionsgeschwindigkeit ist in Schichten fl{\"u}ssigkristalliner Polymeren deutlich geringer, jedoch lassen sich h{\"o}here Werte der Doppelbrechung und des Dichroismus erreichen. In Copolymeren bewirkt die Photoorientierung der Azobenzen-Seitengruppen eine kooperative Orientierung von formanisotropen Seitengruppen. Die Mesogenit{\"a}t der nicht-photochromen Seitengruppen erh{\"o}ht das Ausmaß der induzierten optischen Anisotropie. Die Stabilit{\"a}t der induzierten Doppelbrechung und des Dichroismus wird durch diese Gruppen gesteigert. In Schichten fl{\"u}ssigkristalliner Polymeren wird die induzierte optische Anisotropie beim Tempern im Bereich der Mesophasen erheblich verst{\"a}rkt. Dabei reicht ein geringes Maß an induzierter Anisotropie aus, um Doppelbrechungs- und Dichroismuswerte zu erzielen, wie sie f{\"u}r LC-Dom{\"a}nen typisch sind. In orientierten Schichten von Azobenzen-Polymeren wird das Resultat der linear polarisierten Bestrahlung durch die St{\"a}rke der anisotropen Wechselwirkungen in den fl{\"u}ssigkristallinen Dom{\"a}nen oder den LB-Multilayern bestimmt. Eine lichtinduzierte Reorientierung kann nur erreicht werden, wenn diese Wechselwirkungen {\"u}berwunden werden k{\"o}nnen. Erfolgt eine Photoreorientierung in den orientierten Polymerschichten, werden in Copolymeren formanisotrope Seitengruppen ebenfalls kooperativ reorientiert. Eine vorgelagerte UV-Bestrahlung kann durch Erzeugung eines hohen Anteils an nicht-mesogenen Z-Isomeren die anisotropen Wechselwirkungen stark schw{\"a}chen und so die Seitengruppen entkoppeln. Aus diesem Zustand erfolgt die Photoreorientierung mit einer der Photoorientierung in isotropen Schichten vergleichbaren Effizienz. Die erarbeiteten Struktur-Eigenschafts-Beziehungen liefern einen Beitrag zur Optimierung derartiger Materialien f{\"u}r Anwendungen in den Bereichen optischer Funktionsschichten, holographischer Datenspeicherung oder der Generierung von Oberfl{\"a}chenreliefgittern.},
  subject      = {Fl{\"u}ssigkristalline Polymere},
  language  = {de}
}
@phdthesis{Kumru2018,
  author    = {Kumru, Baris},
  title     = {Utilization of graphitic carbon nitride in dispersed media},
  doi       = {10.25932/publishup-42733},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427339},
  school      = {Universit{\"a}t Potsdam},
  pages     = {III, 190},
  year      = {2018},
  abstract  = {Utilization of sunlight for energy harvesting has been foreseen as sustainable replacement for fossil fuels, which would also eliminate side effects arising from fossil fuel consumption such as drastic increase of CO2 in Earth atmosphere. Semiconductor materials can be implemented for energy harvesting, and design of ideal energy harvesting devices relies on effective semiconductor with low recombination rate, ease of processing, stability over long period, non-toxicity and synthesis from abundant sources. Aforementioned criteria have attracted broad interest for graphitic carbon nitride (g-CN) materials, metal-free semiconductor which can be synthesized from low cost and abundant precursors. Furthermore, physical properties such as band gap, surface area and absorption can be tuned. g-CN was investigated as heterogeneous catalyst, with diversified applications from water splitting to CO2 reduction and organic coupling reactions. However, low dispersibility of g-CN in water and organic solvents was an obstacle for future improvements. Tissue engineering aims to mimic natural tissues mechanically and biologically, so that synthetic materials can replace natural ones in future. Hydrogels are crosslinked networks with high water content, therefore are prime candidates for tissue engineering. However, the first requirement is synthesis of hydrogels with mechanical properties that are matching to natural tissues. Among different approaches for reinforcement, nanocomposite reinforcement is highly promising. This thesis aims to investigate aqueous and organic dispersions of g-CN materials. Aqueous g-CN dispersions were utilized for visible light induced hydrogel synthesis, where g-CN acts as reinforcer and photoinitiator. Varieties of methodologies were presented for enhancing g-CN dispersibility, from co-solvent method to prepolymer formation, and it was shown that hydrogels with diversified mechanical properties (from skin-like to cartilage-like) are accessible via g-CN utilization. One pot photografting method was introduced for functionalization of g-CN surface which provides functional groups towards enhanced dispersibility in aqueous and organic media. Grafting vinyl thiazole groups yields stable additive-free organodispersions of g-CN which are electrostatically stabilized with increased photophysical properties. Colloidal stability of organic systems provides transparent g-CN coatings and printing g-CN from commercial inkjet printers. Overall, application of g-CN in dispersed media is highly promising, and variety of materials can be accessible via utilization of g-CN and visible light with simple chemicals and synthetic conditions. g-CN in dispersed media will bridge emerging research areas from tissue engineering to energy harvesting in near future.},
  language  = {en}
}
@phdthesis{Markushyna2020,
  author    = {Markushyna, Yevheniia},
  title     = {Modern photoredox transformations applied to the needs of organic synthesis},
  doi       = {10.25932/publishup-47766},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-477661},
  school      = {Universit{\"a}t Potsdam},
  pages     = {275},
  year      = {2020},
  abstract  = {Abstract. Catalysis is one of the most effective tools for the highly efficient assembly of complex molecular structures. Nevertheless, it is mainly represented by transition metal-based catalysts and typically is an energy consuming process. Therefore, photocatalysis utilizing solar energy is one of the appealing approaches to overcome these problems. A great alternative to classic transition metal-based photocatalysts, carbon nitrides, a group of organic polymeric semiconductors, have already shown their efficiency in water splitting, CO2 reduction, and organic pollutants degradation. However, these materials have also a great potential for the use in functionalization of complex organic molecules for synthetic needs as it was shown in recent years. This work addresses the challenge to develop efficient system for heterogeneous organic photocatalysis, employing cheap and environmentally benign photocatalysts - carbon nitrides. Herein, fundamental properties of semiconductors are studied from the organic chemistry standpoint; the inherent properties of carbon nitrides, such as ability to accumulate electrons, are deeply investigated and their effect on the reaction outcome is established. Thus, understanding of the electron charging processes allowed for the synthesis of otherwise hardly-achieved diazetidines-1,3 by tetramerization of benzylamines. Furthermore, the high electron capacity of Potassium Poly(heptazine imide)s (K-PHI) made possible a multi-electron reduction of aromatic nitro compounds to bare or formylated anilines. Additionally, two deep eutectic solvents (DES) were designed as a sustainable reaction media and reducing reagent for this reaction. Eventually, the high oxidation ability of carbon nitride K-PHI is employed in a challenging reaction of halide anion oxidation (Cl―, Br―) to accomplish electrophilic substitution in aromatic ring. The possibility to utilize NaCl solution (seawater mimetic) for the chlorination of electron rich arenes was shown. Eventually, light itself is used as a tool in a chromoselective photocatalytic oxidation of aromatic thiols and thioacetatas to three different compounds, using UV, blue, and red LEDs. All in all, the work enhances understanding the mechanism of heterogeneous photocatalysis in synthetic organic reactions and therefore, is a step forward to the sustainable methods of synthesis in organic chemistry.},
  language  = {en}
}
@phdthesis{Pavashe2017,
  author    = {Pavashe, Prashant},
  title     = {Synthesis and transformations of 2-thiocarbohydrates},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-397739},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 132},
  year      = {2017},
  abstract  = {I. Ceric ammonium nitrate (CAN) mediated thiocyanate radical additions to glycals In this dissertation, a facile entry was developed for the synthesis of 2-thiocarbohydrates and their transformations. Initially, CAN mediated thiocyanation of carbohydrates was carried out to obtain the basic building blocks (2-thiocyanates) for the entire studies. Subsequently, 2-thiocyanates were reduced to the corresponding thiols using appropriate reagents and reaction conditions. The screening of substrates, stereochemical outcome and the reaction mechanism are discussed briefly (Scheme I). Scheme I. Synthesis of the 2-thiocyanates II and reductions to 2-thiols III \& IV. An interesting mechanism was proposed for the reduction of 2-thiocyanates II to 2-thiols III via formation of a disulfide intermediate. The water soluble free thiols IV were obtained by cleaving the thiocyanate and benzyl groups in a single step. In the subsequent part of studies, the synthetic potential of the 2-thiols was successfully expanded by simple synthetic transformations. II. Transformations of the 2-thiocarbohydrates The 2-thiols were utilized for convenient transformations including sulfa-Michael additions, nucleophilic substitutions, oxidation to disulfides and functionalization at the anomeric position. The diverse functionalizations of the carbohydrates at the C-2 position by means of the sulfur linkage are the highlighting feature of these studies. Thus, it creates an opportunity to expand the utility of 2-thiocarbohydrates for biological studies. Reagents and conditions: a) I2, pyridine, THF, rt, 15 min; b) K2CO3, MeCN, rt, 1 h; c) MeI, K2CO3, DMF, 0 °C, 5 min; d) Ac2O, H2SO4 (1 drop), rt, 10 min; e) CAN, MeCN/H2O, NH4SCN, rt, 1 h; f) NaN3, ZnBr2, iPrOH/H2O, reflux, 15 h; g) NaOH (1 M), TBAI, benzene, rt, 2 h; h) ZnCl2, CHCl3, reflux, 3 h. Scheme II. Functionalization of 2-thiocarbohydrates. These transformations have enhanced the synthetic value of 2-thiocarbohydrates for the preparative scale. Worth to mention is the Lewis acid catalyzed replacement of the methoxy group by other nucleophiles and the synthesis of the (2→1) thiodisaccharides, which were obtained with complete β-selectivity. Additionally, for the first time, the carbohydrate linked thiotetrazole was synthesized by a (3 + 2) cycloaddition approach at the C-2 position. III. Synthesis of thiodisaccharides by thiol-ene coupling. In the final part of studies, the synthesis of thiodisaccharides by a classical photoinduced thiol-ene coupling was successfully achieved. Reagents and conditions: 2,2-Dimethoxy-2-phenylacetophenone (DPAP), CH2Cl2/EtOH, hv, rt. Scheme III. Thiol-ene coupling between 2-thiols and exo-glycals. During the course of investigations, it was found that the steric hindrance plays an important role in the addition of bulky thiols to endo-glycals. Thus, we successfully screened the suitable substrates for addition of various thiols to sterically less hindered alkenes (Scheme III). The photochemical addition of 2-thiols to three different exo-glycals delivered excellent regio- and diastereoselectivities as well as yields, which underlines the synthetic potential of this convenient methodology.},
  language  = {en}
}