TY - JOUR A1 - Nöchel, Ulrich A1 - Reddy, Chaganti Srinivasa A1 - Wang, Ke A1 - Cui, Jing A1 - Zizak, Ivo A1 - Behl, Marc A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers JF - Journal of Materials Chemistry A, Materials for energy and sustainability N2 - Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units. Y1 - 2015 U6 - https://doi.org/10.1039/c4ta06586g SN - 2050-7488 SN - 2050-7496 VL - 16 IS - 3 SP - 8284 EP - 8293 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Schilde, Uwe A1 - Kelling, Alexandra A1 - Umbreen, Sumaira A1 - Linker, Torsten T1 - Crystal structures of three bicyclic carbohydrate derivatives JF - Acta crystallographica Section E ; Crystallographic communications N2 - The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis(acetyloxy)-7-oxo-2-oxabicyclo- [4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acetyloxy-7- hydroxyimino-2-oxobicyclo[4.2.0]octan-4-yl acetate, C11H15NO6, (II), and [(3aR,5R,6R,7R,7aS)-6,7-bis(acetyloxy)-2-oxooctahydropyrano[3,2-b]pyrrol-5- yl]methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings. KW - crystal structure KW - carbohydrate deriv­atives KW - conformation KW - configuration Y1 - 2016 U6 - https://doi.org/10.1107/S2056989016018727 SN - 2056-9890 VL - 72 IS - 12 SP - 1839 EP - 1844 PB - IUCR CY - Chester ER - TY - JOUR A1 - Morgner, Frank A1 - Bennemann, Mark A1 - Cywiński, Piotr J. A1 - Kollosche, Matthias A1 - Górski, Krzysztof A1 - Pietraszkiewicz, Marek A1 - Geßner, André A1 - Löhmannsröben, Hans-Gerd T1 - Elastic FRET sensors for contactless pressure measurement JF - RSC Advances : an international journal to further the chemical sciences N2 - Contactless pressure monitoring based on Forster resonance energy transfer between donor/acceptor pairs immobilized within elastomers is demonstrated. The donor/acceptor energy transfer is employed by dispersing terbium(III) tris[(2-hydroxybenzoyl)-2-aminoethyl] amine complex (LLC, donor) and CdSe/ZnS quantum dots (QD655, acceptor) in styrene-ethylene/buthylene-styrene (SEBS) and poly(dimethylsiloxane) (PDMS). The continuous monitoring of QD luminescence showed a reversible intensity change as the pressure signal is alternated between two stable states indicating a pressure sensitivity of 6350 cps kPa(-1). Time-resolved measurements show the pressure impact on the FRET signal due to an increase of decay time (270 ms up to 420 ms) for the donor signal and parallel drop of decay time (170 mu s to 155 mu s) for the acceptor signal as the net pressure applied. The LLC/QD655 sensors enable a contactless readout as well as space resolved monitoring to enable miniaturization towards smaller integrated stretchable opto-electronics. Elastic FRET sensors can potentially lead to developing profitable analysis systems capable to outdo conventional wired electronic systems (inductive, capacitive, ultrasonic and photoelectric sensors) especially for point-of-care diagnostics, biological monitoring required for wearable electronics. Y1 - 2017 U6 - https://doi.org/10.1039/c7ra06379b SN - 2046-2069 VL - 7 SP - 50578 EP - 50583 PB - RSC Publishing CY - Cambridge ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Thünemann, Andreas F. A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Undulated Gold Nanoplatelet Superstructures BT - In Situ Growth of Hemispherical Gold Nanoparticles onto the Surface of Gold Nanotriangles JF - Langmuir N2 - Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor. Y1 - 2018 U6 - https://doi.org/10.1021/acs.langmuir.7b02898 SN - 0743-7463 VL - 34 IS - 15 SP - 4584 EP - 4594 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Holland-Moritz, Henry A1 - Graupner, Julia A1 - Möller, Wolfhard A1 - Pacholski, Claudia A1 - Ronning, Carsten T1 - Dynamics of nanoparticle morphology under low energy ion irradiation JF - Nanotechnology N2 - If nanostructures are irradiated with energetic ions, the mechanism of sputtering becomes important when the ion range matches about the size of the nanoparticle. Gold nanoparticles with diameters of similar to 50 nm on top of silicon substrates with a native oxide layer were irradiated by gallium ions with energies ranging from 1 to 30 keV in a focused ion beam system. High resolution in situ scanning electron microscopy imaging permits detailed insights in the dynamics of the morphology change and sputter yield. Compared to bulk-like structures or thin films, a pronounced shaping and enhanced sputtering in the nanostructures occurs, which enables a specific shaping of these structures using ion beams. This effect depends on the ratio of nanoparticle size and ion energy. In the investigated energy regime, the sputter yield increases at increasing ion energy and shows a distinct dependence on the nanoparticle size. The experimental findings are directly compared to Monte Carlo simulations obtained from iradina and TRI3DYN, where the latter takes into account dynamic morphological and compositional changes of the target. KW - ion beam KW - nanoparticles KW - sputtering KW - Monte Carlo KW - in situ Y1 - 2018 U6 - https://doi.org/10.1088/1361-6528/aac36c SN - 0957-4484 SN - 1361-6528 VL - 29 IS - 31 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre BT - simple means to characterize the electron distribution of carbenes JF - Magnetic resonance in chemistry N2 - Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures). KW - C-13 chemical shift KW - carbenes KW - zwitterions KW - carbene electron deficiency KW - nucleus-independent chemical shifts (NICS) KW - through space NMR shieldings KW - (TSNMRS) Y1 - 2019 U6 - https://doi.org/10.1002/mrc.4979 SN - 0749-1581 SN - 1097-458X VL - 58 IS - 3 SP - 280 EP - 292 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Schimka, Selina A1 - Klier, Dennis Tobias A1 - de Guerenu, Anna Lopez A1 - Bastian, Philipp A1 - Lomadze, Nino A1 - Kumke, Michael Uwe A1 - Santer, Svetlana T1 - Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator JF - Journal of physics : Condensed matter N2 - Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm-3(+) or Er-3(+) as activator ions, the UCNPs provide emissions in the spectral range of 450 nm < lambda(em) < 480 nm (for Tm-3(+), three and four photon induced emission) or 525 nm < lambda(em) < 545 nm (for Er-3(+), two photon induced emission), respectively. Especially for UCNPs containing Tm-3(+) a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (lambda(ex) = 976 nm) in the presence of the Tm-3(+)-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl3) in contrast to water, which shows a distinct absorption in the NIR. KW - upconversion nanoparticles KW - azobenzene containing surfactants KW - kinetic of cis-trans isomerization Y1 - 2019 U6 - https://doi.org/10.1088/1361-648X/aafcfa SN - 0953-8984 SN - 1361-648X VL - 31 IS - 12 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Haubitz, Toni A1 - Fudickar, Werner A1 - Linker, Torsten A1 - Kumke, Michael Uwe T1 - pH-sensitive fluorescence switching of pyridylanthracenes BT - the effect of the isomeric pattern JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - 9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range. KW - Absorption KW - Aromatic compounds KW - Fluorescence KW - Hydrocarbons KW - Reaction mechanisms Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpca.0c09911 SN - 1089-5639 SN - 1520-5215 VL - 124 IS - 52 SP - 11017 EP - 11024 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Perovic, Milena A1 - Qin, Qing A1 - Oschatz, Martin T1 - From molecular precursors to nanoparticles BT - tailoring the adsorption properties of porous carbon materials by controlled chemical functionalization JF - Advanced functional materials N2 - Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications. KW - composites KW - heteroatoms KW - metal species KW - porous carbon materials KW - surface KW - functionalization Y1 - 2020 U6 - https://doi.org/10.1002/adfm.201908371 SN - 1616-301X SN - 1616-3028 VL - 30 IS - 41 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yeste, Maria Pilar A1 - Primus, Philipp-Alexander A1 - Alcantara, Rodrigo A1 - Cauqui, Miguel Angel A1 - Calvino, Juan Jose A1 - Pintado, José María A1 - Blanco, Ginesa T1 - Surface characterization of two Ce0.62Zr0.38O2 mixed oxides with different reducibility JF - Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces N2 - This paper presents a study of the surface properties of two Ce/Zr mixed oxides with different reducibility, obtained by applying distinct thermal ageing treatments to an oxide with the composition Ce0.62Zr0.38O2. The surface composition was investigated by XPS. Chemical reactivity of the surface was studied by adsorption of the probe molecules CO2, D-2 and methanol. Nanostructural characterization was carried out by XRD, Raman and high-resolution Eu3+ spectroscopy (FLNS). The characterization showed only slight variations in surface composition and bulk Ce-Zr distribution, but hardy differences concerning the type and strength of acidic surface centres, as well as strong differences in the ability to dissociate hydrogen. Structural variations between both samples were identified by comparing the optical spectra of Eu3+ in surface doped samples. KW - Ce/Zr KW - Surface properties KW - Reactive adsorption KW - Hydrogen activation Y1 - 2020 U6 - https://doi.org/10.1016/j.apsusc.2019.144255 SN - 0169-4332 SN - 1873-5584 VL - 503 PB - Elsevier CY - Amsterdam ER -