38 research outputs found
Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium-Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water
No full textQuinones play a key role as primary electron acceptors in natural photosynthesis, and their reduction is known to be facilitated by hydrogen-bond donors or protonation. In this study, the influence of hydrogen-bond donating solvents on the thermodynamics and kinetics of intramolecular electron transfer between Ru(bpy)32+ (bpy = 2,2′-bipyridine) and 9,10-anthraquinone redox partners linked together via one up to three p-xylene units was investigated. Addition of relatively small amounts of hexafluoroisopropanol to dichloromethane solutions of these rigid rodlike donor–bridge–acceptor molecules is found to accelerate intramolecular Ru(bpy)32+-to-anthraquinone electron transfer substantially because anthraquinone reduction occurs more easily in the presence of the strong hydrogen-bond donor. Similarly, the rates for intramolecular electron transfer are significantly higher in acetonitrile/water mixtures than in dry acetonitrile. In dichloromethane, an increase in the association constant between hexafluoroisopropanol and anthraquinone by more than 1 order of magnitude following quinone reduction points to a significant strengthening of the hydrogen bonds between the hydroxyl group of hexafluoroisopropanol and the anthraquinone carbonyl functions. The photoinduced intramolecular long-range electron transfer process thus appears to be followed by proton motion; hence the overall photoinduced reaction may be considered a variant of stepwise proton-coupled electron transfer (PCET) in which substantial proton density (rather than a full proton) is transferred after the electron transfer has occurred
Die Tugenden eines recht adelichen Land-Lebens, betrachtete bey dem Hochadelichen Leichen-Begängniß Des Hochwohlgebohrnen Herrn, Herrn Hanß George von Schütz, Hochadelichen Lehn- und Gerichts-Herrn auf Erdmannsdorff, als Dieselben im 80sten Jahr ihres ruhmvollen Alters den 19. Febr. 1738. ... das Land der Trübsal mit den ... Wohnungen des Paradieses verwechselt hatten, den 24. Febr. 1738. in Erdmannsdorff ... vollzogen wurde, Ein ... unterthäniger Diener M. Johann George Walther, d. Z. Inform. der Hochadel. Schützischen Enckel
No full textTrauerschrift auf Hanss George von Schütz auf Erdmannsdorff, 24. Febr. 1738Vorlageform des Erscheinungsvermerks: Chemnitz, gedruckt mit Stößelischen Schrifften
Accelerated hole transfer across a molecular double barrier
No full textWe report on a dyad in which photoinduced hole transfer through a non-uniform molecular double barrier is more than one order of magnitude more rapid than hole transfer across a comparable uniform (rectangular) tunneling barrier.Swiss National Science foundation [PP002-110611
Cyclometalated Iridium(III) Complexes as Photosensitizers for Long‐Range Electron Transfer: Occurrence of a Coulomb Barrier
No full textSix cyclometalated iridium(III) complexes were investigated to assess their potential as photosensitizers for long-range electron transfer, and two of them were incorporated directly into covalent donor-bridge-acceptor molecules. The influence of ligand substitutions on the excited-state properties and the photoredox behavior of the iridium complexes was explored by optical absorption, steady-state and time-resolved luminescence spectroscopy, as well as by electrochemical methods. Bimolecular electron transfer between the photoexcited complexes and 10-inethylphenothiazine and methylviologen was found to be only weakly dependent on the ligand substitutions. Intramolecular long-range electron transfer from phenothiazine to photoexcited iridium(III) in the dyads is slow due to the occurrence of a Coulomb barrier. Consequently, an electron-transfer photoproduct is only observable in the transient absorption spectrum of a donor-bridge-acceptor molecule with a fluorinated photosensitizer that exhibits a very long excited-state lifetime. A flash-quench technique is necessary for detection of an electron-transfer product in the dyad with a non-fluorinated photosensitizer. The occurrence of a Coulomb barrier associated with intramolecular (excited-state) long-range electron transfer in the dyads with cyclometalated iridium(III) photosensitizers represents an important difference to previously investigated similar donor-bridge-acceptor molecules with photosensitizers based on d(6) metal diimine complexes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009
Importance of covalence, conformational effects and tunneling-barrier heights for long-range electron transfer: Insights from dyads with oligo-p-phenylene, oligo-p-xylene and oligo-p-dimethoxybenzene bridges
No full textThis review reports on our recent studies of phototriggered charge transfer in rigid rod-like donor-bridge-acceptor molecules in liquid solution as well as between randomly dispersed electron donors and acceptors in frozen organic glasses. Investigation of the distance dependence of the rates of these reactions provides detailed insight into the various factors that govern long-range charge transfer efficiencies. The importance of covalence can be probed by a comparison of charge tunneling through a frozen toluene matrix to tunneling across an oligo-p-xylene bridge. The distance decay constants for these two processes are beta = 1.26 angstrom(-1) and beta = 0.52 angstrom(-1), respectively, indicating that charge tunneling across a covalent xylene-xylene contact is similar to 2 orders of magnitude more efficient than that across a noncovalent toluene-toluene contact. Conformational effects were investigated by comparing hole tunneling across oligo-p-xylene and oligo-p-phenylene bridges. The latter are significantly more pi-conjugated and mediate long-range hole tunneling with beta = 0.21 angstrom(-1) between a ruthenium-phenothiazine donor-acceptor couple. Quantitative analysis indicates that in this particular instance, tunneling across a phenylene-phenylene contact is roughly 50 times more efficient than tunneling across a xylene-xylene contact. The use of oligo-p-dimethoxybenzene wires instead of the structurally very similar oligo-p-xylene bridges was found to lead to a strong acceleration of long-range hole transfer rates: The 23.5-angstrom charge transfer step across four xylene units occurs within 20 mu s, but the charge transfer over the same distance across four dimethoxybenzene units takes only 17 ns. This is attributed to a tunneling-barrier effect that is caused by a large difference in oxidation potentials between the two types of bridges. (C) 2009 Elsevier B.V. All rights reserved
Die überschwengliche Gnaden-Fülle Jesu Christi
No full texteiner christlichen Gemeind den 28. Christmonat 1755 angepriesen von David Anthoni StäheliImpressum gemäss Vorlage: "St. Gallen / gedruckt bey Leonhard Dieth, 1756. Und zufinden bey Hanss Joachim Stäheli, Praeceptor
Photoinduced Processes in Fluorene‐Bridged Rhenium–Phenothiazine Dyads – Comparison of Electron Transfer Across Fluorene, Phenylene, and Xylene Bridges
No full textThe photoinduced processes occurring after pulsed laser excitation of a series of donor–bridge–acceptor molecules comprising a phenothiazine electron donor, variable-length fluorene bridges, and a rhenium(I) electron acceptor were investigated. A dyad with a single fluorene bridge unit exhibits electron transfer from phenothiazine to the rhenium(I) complex upon photoexcitation, whereas in dyads with fluorene oligomers bridge-localized triplet excited states are formed rather than electron transfer products. In the monofluorene-bridged system with a donor–acceptor distance of ca. 15 Å, electron transfer occurs with a time constant of 1.9 ns. The equidistant electron transfer between the same donor and acceptor is considerably slower across a biphenyl bridge (3.9 ns) or a bi-p-xylene spacer (20 ns). This finding is interpreted in terms of different tunneling barrier heights associated with the charge transfer across the three different types of molecular bridges
Standing In Between Two Mirrors: Queer Reflections in the Work of Geoffrey Farmer
No full textThis thesis offers a queer reading of the artistic practice of Canadian artist Geoffrey Farmer (b.1967) by situating queerness as the foundation for Farmer’s approach to artmaking. This thesis considers Farmer’s practice between 1992 and 2017, contextualizing the artist’s work within the shifting landscape of LGBTQ+ politics. This twenty-five-year frame contemplates the different realities for gay men, from the peak of the AIDS crisis to the legalization of same-sex marriage in North America. This thesis comprises of three chapters that examine the artist’s engagements with the future, past, and present. The author employs queer theory as a lens to consider Farmer’s vast practice as it provides a historical and theoretical framework that unfolds alongside the artist’s career. Various concepts from studies on queer temporalities are applied to make sense of the artist’s relation to time and better comprehend his depictions of it. Chapter 1 examines the artist’s emerging career in the 1990s and explores early works that depicted homosexual desire and advocated for gay identity. Early drawings, videos, and installations inspired by science fiction and popular culture are read here for aspects of queer futurity. Chapter 2 focuses on Farmer’s practice in the 2000s and analyzes his better-known installations that deconstruct and re-organize space and time. The author maps Farmer’s interests in archives and reads his disruptive acts as efforts of ‘queering’ the past. This research culminates with a critical reading of the artist’s installation, a way out of the mirror (2017), at the Canada pavilion for the fifty-seventh Venice Biennale. Chapter 3 examines how this prestige coincided with the country’s sesquicentennial anniversary, also known as ‘Canada 150.’ The author contemplates the artist’s personal narratives platformed on this national stage during this political moment through readings of homonationalism to unpack what was at stake in the present. Throughout the thesis, the author argues for the need and value of applying a queer perspective to Farmer’s work as it offers a nuanced understanding of the artist’s illustrious career
Non-probabilistic finite element analysis for parametric uncertainty treatment in applied mechanics: Recent advances
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