TY  - JOUR
A1  - Alrefai, Anas
A1  - Mondal, Suvendu Sekhar
A1  - Wruck, Alexander
A1  - Kelling, Alexandra
A1  - Schilde, Uwe
A1  - Brandt, Philipp
A1  - Janiak, Christoph
A1  - Schoenfeld, Sophie
A1  - Weber, Birgit
A1  - Rybakowski, Lawrence
A1  - Herrman, Carmen
A1  - Brennenstuhl, Katlen
A1  - Eidner, Sascha
A1  - Kumke, Michael Uwe
A1  - Behrens, Karsten
A1  - Günter, Christina
A1  - Müller, Holger
A1  - Holdt, Hans-Jürgen
T1  - Hydrogen-bonded supramolecular metal-imidazolate frameworks: gas sorption, magnetic and UV/Vis spectroscopic properties
JF  - Journal of Inclusion Phenomena and Macrocyclic Chemistry
N2  - By varying reaction parameters for the syntheses of the hydrogen-bonded metal-imidazolate frameworks (HIF) HIF-1 and HIF-2 (featuring 14 Zn and 14 Co atoms, respectively) to increase their yields and crystallinity, we found that HIF-1 is generated in two different frameworks, named as HIF-1a and HIF-1b. HIF-1b is isostructural to HIF-2. We determined the gas sorption and magnetic properties of HIF-2. In comparison to HIF-1a (Brunauer-Emmett-Teller (BET) surface area of 471m(2) g(-1)), HIF-2 possesses overall very low gas sorption uptake capacities [BET(CO2) surface area=85m(2) g(-1)]. Variable temperature magnetic susceptibility measurement of HIF-2 showed antiferromagnetic exchange interactions between the cobalt(II) high-spin centres at lower temperature. Theoretical analysis by density functional theory confirmed this finding. The UV/Vis-reflection spectra of HIF-1 (mixture of HIF-1a and b), HIF-2 and HIF-3 (with 14 Cd atoms) were measured and showed a characteristic absorption band centered at 340nm, which was indicative for differences in the imidazolate framework.
KW  - Gas-sorption
KW  - Ligand design
KW  - Magnetic properties
KW  - Supramolecular chemistry
KW  - Solvothermal synthesis
Y1  - 2019
U6  - https://doi.org/10.1007/s10847-019-00926-6
SN  - 1388-3127
SN  - 1573-1111
VL  - 94
IS  - 3-4
SP  - 155
EP  - 165
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Müller, Katharina
A1  - Foerstendorf, Harald
A1  - Steudtner, Robin
A1  - Tsushima, Satoru
A1  - Kumke, Michael Uwe
A1  - Lefèvre, Grégory
A1  - Rothe, Jörg
A1  - Mason, Harris
A1  - Szabó, Zoltán
A1  - Yang, Ping
A1  - Adam, Christian K. R.
A1  - André, Rémi
A1  - Brennenstuhl, Katlen
A1  - Chiorescu, Ion
A1  - Cho, Herman M.
A1  - Creff, Gaëlle
A1  - Coppin, Frédéric
A1  - Dardenne, Kathy
A1  - Den Auwer, Christophe
A1  - Drobot, Björn
A1  - Eidner, Sascha
A1  - Hess, Nancy J.
A1  - Kaden, Peter
A1  - Kremleva, Alena
A1  - Kretzschmar, Jerome
A1  - Krüger, Sven
A1  - Platts, James A.
A1  - Panak, Petra
A1  - Polly, Robert
A1  - Powell, Brian A.
A1  - Rabung, Thomas
A1  - Redon, Roland
A1  - Reiller, Pascal E.
A1  - Rösch, Notker
A1  - Rossberg, André
A1  - Scheinost, Andreas C.
A1  - Schimmelpfennig, Bernd
A1  - Schreckenbach, Georg
A1  - Skerencak-Frech, Andrej
A1  - Sladkov, Vladimir
A1  - Solari, Pier Lorenzo
A1  - Wang, Zheming
A1  - Washton, Nancy M.
A1  - Zhang, Xiaobin
T1  - Interdisciplinary Round-Robin Test on molecular spectroscopy of the U(VI) Acetate System
JF  - ACS omega / American Chemical Society
N2  - A comprehensive molecular analysis of a simple aqueous complexing system. U(VI) acetate. selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.
Y1  - 2019
U6  - https://doi.org/10.1021/acsomega.9b00164
SN  - 2470-1343
VL  - 4
IS  - 5
SP  - 8167
EP  - 8177
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Burek, Katja
A1  - Dengler, Joachim
A1  - Emmerling, Franziska
A1  - Feldmann, Ines
A1  - Kumke, Michael Uwe
A1  - Stroh, Julia
T1  - Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems
JF  - ChemistryOpen
N2  - The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.
KW  - cement admixtures
KW  - cement hydration
KW  - Europium
KW  - luminescence
KW  - SEM
KW  - X-ray diffraction
Y1  - 2019
U6  - https://doi.org/10.1002/open.201900249
SN  - 2191-1363
VL  - 8
IS  - 12
SP  - 1441
EP  - 1452
PB  - Wiley-VCH-Verl.
CY  - Weinheim
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  - John, Leonard
A1  - Wessig, Pablo
A1  - Kumke, Michael Uwe
T1  - Photophysics of Acyl- and Ester-DBD Dyes
BT  - Quadrupole-Induced Solvent Relaxation Investigated by Transient Absorption Spectroscopy
JF  - the journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - A new generation of wavelength-tunable, fluorescent dyes, so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes, were developed a few years ago, and they showed great potential as probes, for example, for fluorescence microscopy. However, their photophysics is not fully explored and leaves open questions regarding their large fluorescence Stokes shifts and sensitivity to solvent conditions of differently substituted DBD dyes. To improve the understanding of the influence of the substitution pattern of the DBD dyes on their respective photophysics, transient absorption spectroscopy (TAS) was used, that is, a pump-probe experiment on the femtosecond timescale. TAS allows measurements of excited states, ground state recovery, solvent relaxation, and fluorescence properties on time scales of up to several nanoseconds. Two different DBD dye samples were investigated: aryl- and ester-substituted DBD dyes. Experiments were carried out in solvents with different polarities using different excitation energies and at different viscosities. Based on the experimental data and theoretical calculations, we were able to determine the conformational changes of the molecule due to electronic excitation and were able to investigate solvent relaxation processes for both types of DBD dyes. By generalizing the theory for quadrupole-induced solvent relaxation developed by Togashi et al., we derived quadrupole moments of both molecules in the ground and excited state. Our data showed differences in the binding of polar solvent molecules to the dyes depending on the substituent on the DBD dye. In the case of water as the solvent, an additional efficient quenching process in the electronically excited state was revealed, which was indicated by the observation of solvated electrons in the TAS signals.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpca.9b02973
SN  - 1089-5639
VL  - 123
IS  - 22
SP  - 4717
EP  - 4726
PB  - American Chemical Society
CY  - Washington
ER  -