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Nachrichten (2013-2017)

10.07.2017 - A New Approach towards More Efficient OLEDs?

Organic light emitting diodes (OLEDs) are nowadays widespread in display and illumination technology. All OLEDs contain molecular emitters to facilitate the transformation of electricity into light. These emitters are often based on precious metals like iridium or require cumbersome synthesis. In a recent paper published together with undefinedAndrew Monkman’s group at Durham university we give experimental evidence that some low cost aromatic carbonyls have a very large potential for this purpose. Read more: undefinedTriplet Harvesting with a Simple Aromatic Carbonyl.

09.09.2016 - Femtosecond Spectroscopy on a Major Component of Bacterial Spores

Bacterial spores are very resistant towards environmental hazards, in particular UV radiation. The role of calcium dipicolinate – a major component of theses spores – in this UV resistance has been debated for decades. In a undefinedrecent publication we provide a comprehensive characterization of the compound by time resolved spectroscopy. Our results show that photo-excited calcium dipicolinate may interact with the DNA of spores. It remains to be seen whether this interaction is beneficial or detrimental to spores.

07.06.2016 - Poster prize for Jakob Nixdorf

Recently, our PhD student Jakob Nixdorf attended the 4th international undefinedRamanFest in Berlin, organized by HORIBA Scientific, in partnership with the Humboldt University of Berlin. We are very happy that his presentation “Femtosecond stimulated Raman microscopy (FSRM) with a 10 kHz acquisition rate” was awarded with one of the poster prizes.

12.04.2016 - Journal Cover

Ortho-di-substitution of benzenes provides the opportunity to study interactions between diverse functional groups in a defined environment. The substituents are forced to distances which allow chemical reactions to occur. In a undefinedFeature Article in the Journal of Photochemistry and Photobiology A, we focus on photoreactive compounds containing nitro and carbonyl groups, which we have been studying for several years. The complex electronic structure of these molecules results in a rich photochemistry on the femto- and picosecond timescale. A combination of femtosecond spectroscopic techniques and quantum chemical calculations shows that all compounds investigated undergo hydrogen transfers via both, singlet and triplet channels. The experiments enabled us to elucidate the mechanisms of prominent photoreactions as the ones of ortho-nitrobenzaldehyde or of nitrobenzene derived photolabile protecting groups.

25.02.2016 - Thioxanthone in apolar solvents: ultrafast internal conversion precedes fast intersystem crossing

Long-lived triplet states of organic molecules play a key role in their photoreactivity. Thus, the principles underlying the population of triplet states are of great importance for photochemistry. In relation with organic photovoltaics and organic light emitting diodes they are presently intensively studied. We have looked at the population of the triplet state of thioxanthone (TX) in cyclohexane via intersystem crossing (ISC). TX is prototypical for a class of molecules undergoing efficient ISC. By means of undefinedfemtosecond spectroscopy the time constant for ISC was determined to be 4 ps. This is in excellent agreement with the value (6 ps) computed by the undefinedMarian group co-authoring the paper. This and undefinedprevious contributions highlight the influence of the solvent on ISC processes. Whereas in protic solvents the initial process is an ISC one here undefinedultrafast internal conversion (IC) precedes the fast ISC.

28.08.2015 - Journal Cover

UV irradiation of the genetic material DNA has deleterious effects ranging from sunburn to skin cancer. Various molecular mechanisms underlie these effects. Among them is the formation of (6-4) photo-lesions. These lesions contain an altered DNA base - a pyrimidinone - which is prone to secondary photoreactions. In our recent cover article undefined"Pyrimidinone: versatile Trojan horse in DNA photodamage?" we show that in addition to Dewar formation and triplet energy transfer also hydrogen abstraction contributes to this secondary photochemistry. Pyrimidinone is indeed a versatile and wily Trojan horse.

02.03.2015 - Beitrag unserer Gruppe zur aktuellen Wochenschau der GDCh

Die UN-Generalversammlung hat das Jahr 2015 als undefinedInternationales Jahr des Lichts und der lichtbasierten Technologien ausgerufen. Im Rahmen dieses Themenjahres finden weltweit zahlreiche Veranstaltungen und Aktionen statt, die die Bedeutung des Lichts für Leben, Wissenschaft und Kultur herausstellen sollen.

Anlässlich des Themenjahres widmet die Gesellschaft Deutscher Chemiker (GDCh) unter anderem ihre aktuelle Wochenschau dem Thema Licht. In der aktuellen Wochenschau werden schon seit Jahren wöchentlich Beiträge zu aktuellen Themen in Chemie und Technik veröffentlicht.

Da unsere Gruppe Licht nutzt, um Erkenntnisse über chemische Prozesse zu gewinnen, ist in der 9. Kalenderwoche ein von uns verfasster Beitrag veröffentlicht worden. Darin wird erläutert, wie sich mittels Laserlicht die schnellsten chemischen Prozesse überhaupt charakterisieren lassen. Den Artikel von S. Fröbel, A. Reiffers und P. Gilch finden Sie undefinedhier.

18.12.2014 - A Photophysical Chimera Deciphered

Light absorption promotes molecules to excited states. This happens whenever a plant utilizes solar energy in photosynthesis, when the retinas of eyes detect light, and also when sun light burns our skin. Such excited states also have tremendous technological relevance. To name only a few fields: Photovoltaics, light emitting diodes, photo-aging of dyes and polymers, and modern microscopy. Excited states come in at least two flavors related with the electron spin: singlet and triplet. These two flavors have grossly different properties. Excited singlet states emit light, a phenomena know as fluorescence and they are usually short-lived. Excited triplet states are “dark” and long-lived. Upon excitation the organic molecule thioxanthone in certain solvents features properties of both flavors. In a joint theoretical and experimental study by the groups of undefinedChristel Marian and Peter Gilch this chimeric behavior was deciphered. In this molecule singlet and triplet states exhibit the same energy allowing for their co-existence. The computations by Marian et al. reproduce the findings like excitation energies, rate constants, and spectral patterns with high accuracy. In the future this will allow designing molecules with such properties which are of interest - for instance - as molecular sensors.

For more information read the papers by undefinedVillnow et al. and undefinedRai-Constapel et al.

Illustration by Eliza Wiszniewska.

01.10.2014 - Posterpreis der GDCh für Anna Reiffers

In diesem Jahr besuchten drei Mitglieder unserer Gruppe (Christian Torres Ziegenbein, Ramona Mundt & Anna Reiffers) die 24. Lecture Conference on Photochemistry, eine Tagung der Fachgruppe Photochemie der GDCh in Köln.
Anna Reiffers präsentierte dabei die Ergebnisse ihrer noch laufenden Masterarbeit in Form eines Posters. Wir freuen uns sehr, dass ihr Poster mit dem Titel „Time Resolved Spectroscopy on Psoralen-DNA Photoaddition“ mit dem Posterpreis der Konferenz ausgezeichnet wurde.

01.07.2014 - Multichannel detectors for FSRM – ideal and real ones

In femtosecond stimulated Raman microscopy spectrally narrow Raman pump (red) and spectrally broad Raman probe (blue) pulses are fed into a scanning microscope. Stimulated Raman interactions alter the probe spectrum. Registration of these alternations puts high demands on the multi-channel detector. Properties of an ideal detector are compared with those of real ones. undefinedB. Marx et al

24.07.2013 - Picosecond Kinetics in a Lab Experiment

Femtosecond spectroscopy and the ultrafast kinetics and dynamics studied thereby are essential for modern physical chemistry. Advanced classes in physical chemistry should thus cover these topics. To give students a “hands-on” experience of ultrafast kinetics we have set up a lab experiment. The experiment relies on the coalescence of IR transitions of an iron carbonyl compound (W. Grevels. et al. J. Am. Chem. Soc. (120 (1998) 10423). Via an analysis of temperature dependent IR spectra the student can determine picosecond time constants for a turnstile motion of the carbonyl ligands. For details see undefinedS. Fröbel et al.

27.06.2013 - Forschungsförderung

Unser Mitarbeiter Sascha Fröbel wird ab Juli 2013 durch ein Stipendium des Verbandes der Chemischen Industrie (Chemiefonds-Stipendium) gefördert. Das Stipendium wurde für ein Projekt zur Untersuchung von DNA-Schädigungen durch exogene Substanzen mittels Femtosekundenspektroskopie bewilligt.

Wir danken dem Verband der Chemischen Industrie für die Unterstützung unserer Forschung.

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