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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Synthesis and characterization of functionalized norbornene monomers and their resulting ring-opening metathesis polymers and copolymersBiberdorf, Joshua David 13 February 2012 (has links)
The work reported herein describes efforts to create ring-opening metathesis block copolymers and homopolymers. The block copolymers were studied to gain insight into the local nanoscale environment of a block copolymer thin film. Additionally, perylene containing homopolymers were characterized in light of their possible use as an n-type material. In the first section of the thesis, the synthesis of diblock copolymers consisting of two blocks with very different dynamics is described. The covalent attachment of a molecular rotor which is sensitive to its local environment allowed the study of the dynamics of the polymers in thin films. The emissive intensity as a function of temperature allowed us to see discontinuity in the rates of change, indicating a change in the local environment corresponding to the transition of the polymer from a glassy to rubbery state. The corresponding temperature, to this event, is known as the glass transition temperature, Tg. Additionally, a polymer featuring a covalently bound n-type molecule, perylene diimide, was synthesized. The photophysical properties, including aggregation in dilute solution, are described. The material is expected to demonstrate the ability to efficiently transport negative charge, acting as n-type material in organic electronics. / text
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Photophysical kinetics in TICT-forming compounds - derivatives of DMABNSukumaran, Murali 21 June 2005 (has links)
Das Hauptaugenmerk der vorliegenden Arbeit richtet sich auf die Untersuchung der photophysikalischen Eigenschaften von Derivaten von N,N-Dimethylaminobenzonitril (DMABN) und N-Phenyl-pyrrolobenzonitril (PBN) als Donor-Akzeptor Verbindungen. Die untersuchten Verbindungen zeichnen sich durch Einführung von Fluor-Substituenten durch eine erhöhte Akzeptorstärke aus, wodurch neue Erkenntnisse bzgl. der intramolekularen Charge-Transfer-Zustände (ICT) gewonnen werden konnten. Hierbei wurden die Ergebnisse zum Verhalten der untersuchten Moleküle im angeregten Zustand mit denen der entsprechenden Basisverbindungen verglichen. Die spektroskopischen und photophysikalischen Eigenschaften wurden sowohl durch die Anwendung der stationären und zeitaufgelösten Fluoreszenzspektroskopie bei Raum- und Tieftemperatur als auch durch Nutzung der transienten Absorptionsspektroskopie in Kombination mit quantenchemischen Berechnungen untersucht. Im Unterschied zu den Basisverbindungen DMABN und PBN zeigen die Spektren der fluorierten Derivate nur eine einzige stark rotverschobene Fluoreszenzbande, die dem ICT-Zustand zugeordnet werden kann. Die extrem kleinen Quantenausbeuten, die typisch für alle fluorierten Derivate sind, können auf die Existenz eines weiteren strahlungslosen Deaktivierungskanals zurückgeführt werden. Der beobachtete ICT kann mit dem TICT-Modell (Twisted intramolecular Charge Transfer), bei dem von einer gegenseitigen Verdrillung der Donor- und Akzeptoreinheiten ausgegangen wird, erklärt werden. Weiterhin wurden die Variation der Verknüpfungsposition zwischen Donor- und Akzeptoreinheit sowie der Einfluss zusätzlicher Akzeptor-Substituenten auf die Eigenschaften der ICT-Zustände untersucht. Durch die Ergebnisse dieser Arbeit konnte ein vertieftes Verständnis über die Ladungstrennungsprozesse in Donor-Akzeptor-Systemen, die sich durch eine starke Solvatochromie und die Existenz von strahlungslosen Deaktivierungskanälen auszeichnen, entwickelt werden. Es konnte die Möglichkeit der Besetzung von zwei verschiedenen ICT-Zuständen (TICT – verboten, mesomerer ICT – erlaubt) gezeigt werden. / The focus of this work is mainly concerned with the investigation of photophysical properties of electron donor-acceptor compounds, namely, derivatives of N,N-dimethylamino benzonitrile (DMABN) and N-phenyl-pyrrolobenzonitrile (PBN). New insights into the intramolecular charge transfer (ICT) states were obtained while dealing with an acceptor moiety of increased strength in the form of fluorinated analogues of both these compounds. The molecules studied in this work have been compared with their corresponding parent compounds to get more useful information on the excited state behaviour. The spectroscopic and photophysical properties were studied using steady-state and time-resolved fluorescence at room and low temperature as well as with transient absorption spectroscopy in conjunction with quantum chemical calculations. Unlike in the parent compounds DMABN and PBN, their fluorinated derivatives show only a single strongly red-shifted fluorescence emitted from the ICT state, and possess low quantum yields. The nearly non-fluorescent behaviour for all of these fluorinated derivatives investigated is due to the presence of a photochemical mechanism additional to that of ICT, which acts as a new non-radiative funnel. The ICT observed in these compounds can be explained by twisting motion taking place between the donor and acceptor moieties. Thus, twisted intramolecular charge transfer (TICT) model supports the observations. Apart from the changes in the strength of the acceptor moieties, the ICT nature has been further explored by changing their linking positions as well as with additional acceptor substituents. From the findings obtained in this work, a deeper understanding of the charge separation processes occurring in donor-acceptor systems with high solvatochromism and non-radiative decay properties was obtained. The possibility for populating two different ICT states (of forbidden nature – TICT, and allowed nature – mesomeric ICT) has been exemplified.
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Exploring Organic Dyes for Grätzel Cells Using Time-Resolved SpectroscopyEl-Zohry, Ahmed M. January 2015 (has links)
Grätzel cells or Dye-Sensitized Solar Cells (DSSCs) are considered one of the most promising methods to convert the sun's energy into electricity due to their low cost and simple technology of production. The Grätzel cell is based on a photosensitizer adsorbed on a low band gap semiconductor. The photosensitizer can be a metal complex or an organic dye. Organic dyes can be produced on a large scale resulting in cheaper dyes than complexes based on rare elements. However, the performance of Grätzel cells based on metal-free, organic dyes is not high enough yet. The dye's performance depends primarily on the electron dynamics. The electron dynamics in Grätzel cells includes electron injection, recombination, and regeneration. Different deactivation processes affect the electron dynamics and the cells’ performance. In this thesis, the electron dynamics was explored by various time-resolved spectroscopic techniques, namely time-correlated single photon counting, streak camera, and femtosecond transient absorption. Using these techniques, new deactivation processes for organic dyes used in DSSCs were uncovered. These processes include photoisomerization, and quenching through complexation with the electrolyte. These deactivation processes affect the performance of organic dyes in Grätzel cells, and should be avoided. For instance, the photoisomerization can compete with the electron injection and produce isomers with unknown performance. Photoisomerization as a general phenomenon in DSSC dyes has not been shown before, but is shown to occur in several organic dyes, among them D149, D102, L0 and L0Br. In addition, D149 forms ground state complexes with the standard iodide/triiodide electrolyte, which directly affect the electron dynamics on TiO2. Also, new dyes were designed with the aim of using ferrocene(s) as intramolecular regenerators, and their dynamics was studied by transient absorption. This thesis provides deeper insights into some deactivation processes of organic dyes used in DSSCs. New rules for the design of organic dyes, based on these insights, can further improve the efficiency of DSSCs.
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Intramolecular Charge Transfer in Dimethylaminobenzonitrile and Related Aromatic NitrilesLee, Jae-kwang 15 December 2009 (has links)
No description available.
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Synthesis of Fluorescent Molecules and their Applications as Viscosity Sensors, Metal Ion Indicators, and Near-Infrared ProbesWang, Mengyuan 01 January 2014 (has links)
The primary focus of this dissertation is the development of novel fluorescent near-infrared molecules for various applications. In Chapter 1, a compound dU-BZ synthesized via Sonogashira coupling reaction methodology is described. A deoxyuridine building block was introduced to enhance hydrophilic properties and reduce toxicity, while an alkynylated benzothiazolium dye was incorporated for near-IR emission and reduce photodamage and phototoxicity that is characteristic of common fluorphores that are excited by UV or visible light. A 30-fold enhancement of fluorescence intensity of dU-BZ was achieved in a viscous environment. Values of fluorescence quantum yields in 99% glycerol/1% methanol (v/v) of varying temperature from 293 K to 343 K, together with fluorescence quantum yields, radiative and nonradiative rate constants and fluorescence lifetimes in glycerol/methanol solutions of varying viscosities from 4.8 to 950 cP were determined. It was found that both fluorescence quantum yields and fluorescence lifetimes increased with increasing viscosity, which is consistent with results predicted by theory. This suggests that the newly designed compound dU-BZ is capable of functioning as a probe of local microviscosity, and was later confirmed by in vitro bioimaging experiments. In Chapter 2, a new BAPTA (O,O*-bis(2-aminophenyl)ethyleneglycol-N,N,N*,N*-tetra acetic acid) and BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based calcium indicator, BAPBO-3, is reported. A new synthetic route was employed to simplify both synthesis and purification, which tend to be low yielding and cumbersome for BAPTA derivatives. Upon excitation, a 1.5-fold increase in fluorescence intensity in buffer containing 39 ?? Ca2+ and a 3-fold increase in fluorescence intensity in buffer containing 1 M Ca2+ was observed; modest but promising fluorescence turn-on enhancements. In Chapter 3, a newly-designed unsymmetrical squaraine dye, SQ3, was synthesized. A one-pot synthesis was employed resulting in a 10% yield, a result that is generally quite favorable for the creation of unsymmetrical squaraines Photophysical and photochemical characterization was conducted in various solvents, and a 678 nm absorption maximum and a 692 nm emission maximum were recorded in DMSO solution with a fluorescence quantum yield of 0.32. In vitro cell studies demonstrated that SQ3 can be used as a near-IR probe for bioimaging.
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Solvatationsdynamik an biologischen Grenzschichten / Solvation dynamics at biological interfacesSeidel, Marco Thomas 05 November 2003 (has links)
No description available.
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