Browsing by Author "Siefermann, Katrin R."
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- ItemCommunication: X-ray coherent diffractive imaging by immersion in nanodroplets(Melville, NY : AIP Publishing LLC, 2015) Tanyag, Rico Mayro P.; Bernando, Charles; Jones, Curtis F.; Bacellar, Camila; Ferguson, Ken R.; Anielski, Denis; Boll, Rebecca; Carron, Sebastian; Cryan, James P.; Englert, Lars; Epp, Sascha W.; Erk, Benjamin; Foucar, Lutz; Gomez, Luis F.; Hartmann, Robert; Neumark, Daniel M.; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Siefermann, Katrin R.; Ullrich, Joachim; Weise, Fabian; Bostedt, Christoph; Gessner, Oliver; Vilesov, Andrey F.Lensless x-ray microscopy requires the recovery of the phase of the radiation scattered from a specimen. Here, we demonstrate a de novo phase retrieval technique by encapsulating an object in a superfluid helium nanodroplet, which provides both a physical support and an approximate scattering phase for the iterative image reconstruction. The technique is robust, fast-converging, and yields the complex density of the immersed object. Images of xenon clusters embedded in superfluid helium droplets reveal transient configurations of quantum vortices in this fragile system.
- ItemEfficient synthesis of triarylamine-based dyes for p-type dye-sensitized solar cells(London : Nature Publishing Group, 2016) Wild, Martin; Griebel, Jan; Hajduk, Anna; Friedrich, Dirk; Stark, Annegret; Abel, Bernd; Siefermann, Katrin R.The class of triarylamine-based dyes has proven great potential as efficient light absorbers in inverse (p-type) dye sensitized solar cells (DSSCs). However, detailed investigation and further improvement of p-type DSSCs is strongly hindered by the fact that available synthesis routes of triarylamine-based dyes are inefficient and particularly demanding with regard to time and costs. Here, we report on an efficient synthesis strategy for triarylamine-based dyes for p-type DSSCs. A protocol for the synthesis of the dye-precursor (4-(bis(4-bromophenyl)amino)benzoic acid) is presented along with its X-ray crystal structure. The dye precursor is obtained from the commercially available 4(diphenylamino)benzaldehyde in a yield of 87% and serves as a starting point for the synthesis of various triarylamine-based dyes. Starting from the precursor we further describe a synthesis protocol for the dye 4-{bis[4′-(2,2-dicyanovinyl)-[1,1′-biphenyl]-4-yl]amino}benzoic acid (also known as dye P4) in a yield of 74%. All synthesis steps are characterized by high yields and high purities without the need for laborious purification steps and thus fulfill essential requirements for scale-up.
- ItemSynthesis and characterization of new photoswitchable azobenzene-containing poly(ε-caprolactones)(London : RSC Publishing, 2016) Appiah, Clement; Siefermann, Katrin R.; Jorewitz, Marcel; Barqawi, Haitham; Binder, Wolfgang H.A novel and efficient strategy in obtaining series of mono- and bi-armed azobenzene-containing poly(ε-caprolactone)s is described, starting from a commercially available azobenzene dye via azide/alkyne-“click”-reactions. The attachment of alkyne-telechelic poly(ε-caprolactone)s (1 kDa and 3 kDa), followed by chromatographic separation, allowed the attachment of either one or two PCl-chains to either side of the azobenzene-dye. The resulting mono- and bi-armed photo-switchable polymers are fully characterized by 2D-NMR techniques and show a high thermal stability. Additionally liquid chromatography at critical conditions (LCCC) coupled to ESI-TOF allowed us to prove the presence of either one or two polymer chains affixed onto the central azobenzene dye.