@phdthesis{Haubitz2021,
  author    = {Haubitz, Toni},
  title     = {Transient absorption spectroscopy},
  doi       = {10.25932/publishup-53509},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-535092},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 176},
  year      = {2021},
  abstract  = {The optical properties of chromophores, especially organic dyes and optically active inorganic molecules, are determined by their chemical structures, surrounding media, and excited state behaviors. The classical optical go-to techniques for spectroscopic investigations are absorption and luminescence spectroscopy. While both techniques are powerful and easy to apply spectroscopic methods, the limited time resolution of luminescence spectroscopy and its reliance on luminescent properties can make its application, in certain cases, complex, or even impossible. This can be the case when the investigated molecules do not luminesce anymore due to quenching effects, or when they were never luminescent in the first place. In those cases, transient absorption spectroscopy is an excellent and much more sophisticated technique to investigate such systems. This pump-probe laser-spectroscopic method is excellent for mechanistic investigations of luminescence quenching phenomena and photoreactions. This is due to its extremely high time resolution in the femto- and picosecond ranges, where many intermediate or transient species of a reaction can be identified and their kinetic evolution can be observed. Furthermore, it does not rely on the samples being luminescent, due to the active sample probing after excitation. In this work it is shown, that with transient absorption spectroscopy it was possible to identify the luminescence quenching mechanisms and thus luminescence quantum yield losses of the organic dye classes O4-DBD, S4-DBD, and pyridylanthracenes. Hence, the population of their triplet states could be identified as the competitive mechanism to their luminescence. While the good luminophores O4-DBD showed minor losses, the S4-DBD dye luminescence was almost entirely quenched by this process. However, for pyridylanthracenes, this phenomenon is present in both the protonated and unprotonated forms and moderately effects the luminescence quantum yield. Also, the majority of the quenching losses in the protonated forms are caused by additional non-radiative processes introduced by the protonation of the pyridyl rings. Furthermore, transient absorption spectroscopy can be applied to investigate the quenching mechanisms of uranyl(VI) luminescence by chloride and bromide. The reduction of the halides by excited uranyl(VI) leads to the formation of dihalide radicals X^(·-2). This excited state redox process is thus identified as the quenching mechanism for both halides, and this process, being diffusion-limited, can be suppressed by cryogenically freezing the samples or by observing these interactions in media with a lower dielectric constant, such as ACN and acetone.},
  language  = {en}
}
@phdthesis{Hildebrandt2006,
  author    = {Hildebrandt, Niko},
  title     = {Lanthanides and quantum dots : time-resolved laser spectroscopy of biochemical F{\"o}rster Resonance Energy Transfer (FRET) systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12686},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {F{\"o}rster Resonance Energy Transfer (FRET) plays an important role for biochemical applications such as DNA sequencing, intracellular protein-protein interactions, molecular binding studies, in vitro diagnostics and many others. For qualitative and quantitative analysis, FRET systems are usually assembled through molecular recognition of biomolecules conjugated with donor and acceptor luminophores. Lanthanide (Ln) complexes, as well as semiconductor quantum dot nanocrystals (QD), possess unique photophysical properties that make them especially suitable for applied FRET. In this work the possibility of using QD as very efficient FRET acceptors in combination with Ln complexes as donors in biochemical systems is demonstrated. The necessary theoretical and practical background of FRET, Ln complexes, QD and the applied biochemical models is outlined. In addition, scientific as well as commercial applications are presented. FRET can be used to measure structural changes or dynamics at distances ranging from approximately 1 to 10 nm. The very strong and well characterized binding process between streptavidin (Strep) and biotin (Biot) is used as a biomolecular model system. A FRET system is established by Strep conjugation with the Ln complexes and QD biotinylation. Three Ln complexes (one with Tb3+ and two with Eu3+ as central ion) are used as FRET donors. Besides the QD two further acceptors, the luminescent crosslinked protein allophycocyanin (APC) and a commercial fluorescence dye (DY633), are investigated for direct comparison. FRET is demonstrated for all donor-acceptor pairs by acceptor emission sensitization and a more than 1000-fold increase of the luminescence decay time in the case of QD reaching the hundred microsecond regime. Detailed photophysical characterization of donors and acceptors permits analysis of the bioconjugates and calculation of the FRET parameters. Extremely large F{\"o}rster radii of more than 100 {\AA} are achieved for QD as acceptors, considerably larger than for APC and DY633 (ca. 80 and 60 {\AA}). Special attention is paid to interactions with different additives in aqueous solutions, namely borate buffer, bovine serum albumin (BSA), sodium azide and potassium fluoride (KF). A more than 10-fold limit of detection (LOD) decrease compared to the extensively characterized and frequently used donor-acceptor pair of Europium tris(bipyridine) (Eu-TBP) and APC is demonstrated for the FRET system, consisting of the Tb complex and QD. A sub-picomolar LOD for QD is achieved with this system in azide free borate buffer (pH 8.3) containing 2 \% BSA and 0.5 M KF. In order to transfer the Strep-Biot model system to a real-life in vitro diagnostic application, two kinds of imunnoassays are investigated using human chorionic gonadotropin (HCG) as analyte. HCG itself, as well as two monoclonal anti-HCG mouse-IgG (immunoglobulin G) antibodies are labeled with the Tb complex and QD, respectively. Although no sufficient evidence for FRET can be found for a sandwich assay, FRET becomes obvious in a direct HCG-IgG assay showing the feasibility of using the Ln-QD donor-acceptor pair as highly sensitive analytical tool for in vitro diagnostics.},
  language  = {en}
}
@phdthesis{Menski2019,
  author    = {Menski, Antonia Isabell},
  title     = {Europium als strukturelle Sonde zur Analyse neuartiger Materialien},
  doi       = {10.25932/publishup-42714},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427141},
  school      = {Universit{\"a}t Potsdam},
  pages     = {181},
  year      = {2019},
  abstract  = {Im Rahmen dieser Arbeit wird anhand von neuartigen Materialien das Potential der Europium-Lumineszenz f{\"u}r die strukturelle Analyse dargestellt. Bei diesen Materialien handelt es sich zum einen um Nanopartikel mit Matrizes aus mehreren Metall-Mischoxiden und Dotierungen durch die Sonde Europium und zum anderen um Metallorganische Netzwerke (MOFs), die mit Neodym , Samarium- und Europium-Ionen beladen sind. Die Synthese der aus der Kombination von Metalloxiden enthaltenen Nanopartikel ist unter milden Bedingungen mithilfe von speziell daf{\"u}r hergestellten Reagenzien erfolgt und hat zu sehr kleinen, amorphen Nanopartikeln gef{\"u}hrt. Durch eine nachfolgende Temperaturbehandlung hat sich die Kristallinit{\"a}t erh{\"o}ht. Damit verbunden haben sich auch die Kristallstruktur sowie die Position des Dotanden Europium ver{\"a}ndert. W{\"a}hrend die etablierte Methode der R{\"o}ntgendiffraktometrie einen Blick auf das Kristallgitter als Gesamtes erm{\"o}glicht, so trifft die Lumineszenz des Europiums durch die Sichtbarkeit einzelner Stark-Aufspaltungen Aussagen {\"u}ber dessen lokale Symmetrien. Die Symmetrie wird durch Sauerstofffehlstellen ver{\"a}ndert, welche die Sauerstoffleitf{\"a}higkeit der Nanopartikel beeinflussen. Diese ist f{\"u}r die Anwendung als Katalysatoren in industriellen Prozessen und ebenso als Sensoren und Therapeutika in biologischen Systemen von Bedeutung. Zur ersten katalytischen Charakterisierung werden die Proben mittels Temperatur-programmierter Reduktion untersucht. Des Weiteren werden die Mischoxid-Nanopartikel auch hinsichtlich ihrer Verwendbarkeit als Matrix in Aufkonversionsprozessen untersucht. Die Metallorganischen Netzwerke eignen sich aufgrund ihrer mikropor{\"o}sen Struktur f{\"u}r Anwendungen in der Speicherung gleichermaßen von Nutzgasen wie auch von Schadstoffen. Ebenfalls ist eine biologische Anwendung denkbar, die insbesondere den Bereich der drug delivery-Reagenzien betrifft. Erfolgt in die mikropor{\"o}sen Strukturen der Metallorganischen Netzwerke die Einlagerung von Lanthanoid-Ionen, so k{\"o}nnen diese bei der entsprechenden Kombination als Weißlicht-Emittierer fungieren. Dabei ist neben den Verh{\"a}ltnissen zwischen den Lanthanoid-Ionen auch die genaue Position innerhalb des Netzwerks sowie die Distanz zu anderen Ionen von Interesse. Zur Untersuchung dieser Fragestellungen wird die Umgebungssensitivit{\"a}t der Europium-Lumineszenz ausgenutzt. Die auf diese Weise festgestellte Formiat-Bildung h{\"a}ngt von zahlreichen Parametern ab. Insgesamt stellt sich die im Rahmen dieser Arbeit verwendete Methodik des Einsatzes von Europium als strukturelle Sonde in h{\"o}chstem Maße vielseitig dar und zeigt seine gr{\"o}ßte St{\"a}rke in der Kombination mit weiteren Methoden der Strukturanalytik. Die auf diese Weise genauestens charakterisierten neuartigen Materialien k{\"o}nnen nun gezielt und anwendungsfokussiert weiterentwickelt werden.},
  language  = {de}
}