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Veröffentlichungen der AG Gräfe

Teilbibliothek Naturwissenschaften: Chemie

Foto: Jan-Peter Kasper (Universität Jena)
Teilbibliothek Naturwissenschaften: Chemie

Referierte Publikationen

Bücher und Buchkapitel

  • Markus Kitzler und Stefanie Gräfe (Eds.),
    Ultrafast Dynamics Driven by Intense Light Pulses.Externer Link
    Springer Series on Atomic, Optical, and Plasma Physics, 978-3-319-20173-3 (2016).
  • Dirk Bender, Leticia González und Stefanie Gräfe,
    Short Introduction to Atomic and Molecular Configuration.
    in: Handbook of Biophotonics, J. Popp, V. V. Tuchin, A. Chiou, S. Heinemann (Eds.), Wiley-VCH Weinheim, Vol. 1(Basics and Techniques), 39-86 (2011).

Sonstige Publikationen

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Hervorgehobene Autoren sind Mitglieder der Forschungsgruppe.

  1. Probing Metal Tip-Induced Bond Weakening of a Reactive Alkyne Center Aligned via a Rigid Triphenylmethane-Based Tripod on Au(111) by TERS and DFT

    Autoren G. Li, S. Mennicken, L. Zhu, S. Ehtesabi, T. Reichenauer, S. Kupfer, D. Schäfer, S. Mehrparvar, G. Haberhauer, Y. Zhang, S. Gräfe, S. Schlücker, Z. Dong ErscheinungsjahrErschienen in:Journal of Raman spectroscopy
    The chemical reactivity of molecules can be controlled by a variety of effects, ranging from chemical reagents to purely physical stimuli. Metal tips employed in scanning probe microscopy are an elegant tool to manipulate reactive centers in single molecules. However, to achieve excellent control over distance and orientation, it is crucial to immobilize the reactive center and align it along the direction of the tip. Here, we aligned a reactive alkyne center via a rigid triphenylmethane-based tripod for upright adsorption on Au(111) for inducing bond weakening in the alkyne moiety by approaching a silver tip. Single-molecule ultrahigh vacuum low-temperature tip-enhanced Raman scattering was employed for probing tip-induced bond weakening in the gap distance range from 550 to 250 pm. Both the ≡C–H stretching at ~3330 cm−¹ and the dominant –C≡C– stretching peak at ~2130 cm−¹ exhibit a shift to smaller wavenumbers due to tip-induced bond weakening and an exponential increase in Raman intensity originating from the increased local electric field in the nanogap. To rationalize the underlying physical contributions and chemical effects of tip-induced bond weakening, density functional theory calculations for gap distances in the range 800 to 100 pm were performed. The computational results confirmed the presence of different gap distance regimes including the onset of Pauli repulsion for short distances; for the latter, the calculations additionally predict structural distortions of the terminal alkyne induced by the nearby metal tip. These findings allow us to set a lower limit for the tip–tripod gap distance in studies requiring an intact upright configuration of the alkyne-tripod, for example, electric field-induced chemistry.
    Universitätsbibliographie Jena:
    fsu_mods_00029568Externer Link

  2. Light to energy carrier conversion by [FeFe]-hydrogenase mimic complexes

    Autor C. Kasahara Erscheinungsjahr
    This thesis provided an overview of photocatalytic applications and underlying mechanisms of light-induced reactions with [FeFe]-H2ase (hydrogenase) mimics. The first project investigated the interaction between a light-harvesting compound and a [FeFe]-H2ase mimic. This study elucidated the effect of a covalent linkage between PS (photosensitiser) and CAT (catalytic centre) in terms of the photoinduced electron transfer mechanism and H2 evolution efficiencies. The second project demonstrated a molecular design strategy of PS-CAT (photosensitiser-catalyst dyad) aimed at enhancing H2 evolution performance. This research confirmed that a benzenthiolate linker enables increased synthetic yield, the introduction of two PSs in the PS-CAT structure, and simultaneous optimisation of the redox potential of the dyad. Two push-pull ligands promote the accessibility of the catalytically active excited-state species. The third project described further photocatalytic applications of an [FeFe]-H2ase mimic dyad. The work revealed that the [FeFe]-H2ase mimic catalyses the CO2 reduction reaction in aqueous media with high product selectivity. Overall, through this thesis, light-to-energy-carrier conversion by [FeFe]-H2ase mimic complexes was successfully accomplished.
    Universitätsbibliographie Jena:
    fsu_mods_00044037Externer Link

  3. Modeling high-order harmonic generation in quantum dots using a real-space tight-binding approach

    Autoren M. Thümmler, A. Croy, U. Peschel, S. Gräfe ErscheinungsjahrErschienen in:The Journal of Chemical Physics : JCP
    Recently, the size-dependence of high-order harmonic generation (HHG) in quantum dots (QDs) has been investigated experimentally. In particular, for longer driving wavelengths and quantum dots smaller than 3 nm, HHG was strongly suppressed; however, there is no computational model capable of describing the strong-field response of such systems. In this work, we introduce a computationally efficient three-dimensional real-space tight-binding model specifically designed for the simulation of HHG in confined systems. The model parameters are meticulously derived from density functional theory calculations for the semiconductor bulk, followed by a process of Wannierization. Our findings demonstrate that the proposed model accurately captures the observed dependency of the HHG yield on the quantum dot size. In addition, we simulate the HHG yield for elliptically polarized pulses for different QD-sizes and driving wavelengths up to 5 μm. The proposed model fills the theoretical void in simulating HHG within medium-sized nanostructures, which cannot be described by methods applied for periodic solids, or small molecules or atoms.
    Universitätsbibliographie Jena:
    fsu_mods_00034842Externer Link

  4. Semiconductor Bloch equations in Wannier gauge with well-behaved dephasing

    Autoren M. Thümmler, T. Lettau, A. Croy, U. Peschel, S. Gräfe ErscheinungsjahrErschienen in:Computer physics communications: an international journal devoted to computational physics and computer programs in physics
    The semiconductor Bloch equations (SBEs) with a dephasing operator for the microscopic polarizations are a well established approach to simulate high-harmonic spectra in solids. We discuss the impact of the dephasing operator on the stability of the numerical integration of the SBEs in the Wannier gauge. It is shown that the commonly used phenomenological approach to apply dephasing is ill-defined in the presence of band crossings and leads to artifacts in the carrier distribution. They are caused by rapid changes of the dephasing operator matrix elements in the Wannier gauge, which render the convergence of the simulation in the stationary basis infeasible. In the comoving basis, also called Houston basis, these rapid changes can be resolved, but only at the cost of a largely increased computation time. As a remedy, we propose a modification of the dephasing operator with reduced magnitude in energetically close subspaces. This approach removes the artifacts in the carrier distribution and significantly speeds up the calculations, while affecting the high-harmonic spectrum only marginally. To foster further development, we provide our parallelized source code.
    Universitätsbibliographie Jena:
    fsu_mods_00029532Externer Link

  5. Efficient Machine Learning Prediction of Solvent-Dependent 1H NMR Chemical Shifts in Zinc Complexes

    Autoren J. Pillay, M. Ringleb, A. Croy, S. Zechel, U. Schubert, S. Gräfe ErscheinungsjahrErschienen in:Journal of computational chemistry : organic, inorganic, physical, biological
    Accurate prediction of NMR chemical shifts in transition metal complexes remains challenging due to the wide range of coordination environments and complex electronic structures of these systems. In this work, we present a machine learning approach (ML) for rapid and accurate prediction of formula presented NMR shifts in zinc complexes across multiple solvent environments. We systematically selected a diverse set of zinc complexes from the transition metal quantum mechanics (tmQM) database using K-means clustering on SOAP descriptors, and performed DFT NMR calculations across five solvents to generate training data. We combine smooth overlap of atomic positions (SOAP) descriptors with tree-based ensemble methods to predict proton chemical shifts. Among several ML algorithms evaluated, LightGBM achieved the best performance on held-out test complexes (MAE = 0.016 ppm, RMSE = 0.028 ppm, formula presented  = 0.99), demonstrating excellent generalization to unseen molecular structures. External validation against experimental NMR data across multiple solvents revealed strong predictive performance ( formula presented  = 0.90, MAE = 0.56 ppm), with exceptional accuracy in methanol ( formula presented  = 0.96) and acetonitrile ( formula presented  = 0.91). Notably, the model demonstrated robust transferability to acetonitrile despite this solvent not being included in the training set. This approach provides a computationally efficient alternative to expensive quantum chemical calculations for predicting formula presented NMR shifts in transition metal complexes, offering prediction times that are orders of magnitude faster while maintaining accuracy comparable to DFT methods, potentially accelerating the characterization and design of organometallic compounds.
    Universitätsbibliographie Jena:
    fsu_mods_00035714Externer Link

  6. Strong field spectroscopy of many-body interactions in solids

    Autoren V. Korolev, T. Lettau, V. Krishna, A. Croy, M. Thümmler, M. Zürch, C. Spielmann, M. Wächtler, U. Peschel, S. Gräfe, G. Soavi, D. Kartashov ErscheinungsjahrErschienen in:Nature Communications
    High-order harmonic generation (HHG) in solids offers a promising route to compact ultrafast sources of quantum light, but its efficiency and coherence are limited by ultrafast dephasing of laser-driven electron–hole polarization. Although widely described by a phenomenological coherence time, the microscopic origin of this dephasing has remained unresolved. Here, we combine wavelength-dependent HHG measurements in monolayer and bulk semiconductors with ab initio many-body calculations of electron–phonon scattering and strong-field simulations. We show that the measured wavelength scaling of the HHG yield is quantitatively reproduced only when semiconductor Bloch equations incorporate momentum-dependent dephasing derived from first principles scattering rates. The calculations reveal that strong-field-driven carriers rapidly enter regions of the Brillouin zone with enhanced electron–phonon scattering, giving rise to effective few-femtosecond dephasing. Our results establish a microscopic foundation for dephasing in solid-state HHG and provide a framework for engineering coherence in strongly driven solids for quantum photonic applications.
    Universitätsbibliographie Jena:
    fsu_mods_00044501Externer Link

  7. Investigation of the dynamic behavior of metallopolymers by combined experimental and theoretical methods

    Autoren M. Jäger, M. Agyemang, W. Schulze, J. Kimmig, T. Bätz, C. Wondraczek, S. Zechel, A. Croy, M. Schmitt, J. Popp, S. Gräfe, M. Hager, U. Schubert ErscheinungsjahrErschienen in:Polymer Chemistry
    In this study, we investigate the structural changes in dynamic metallopolymers during stimulus application, i.e. thermal treatment. For this purpose, we focused on the synthesis of polymers containing terpyridine moieties as ligands in the side chains that were complexed with either iron(ii) or zinc(ii) salts. The resulting crosslinked metallopolymers were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and elemental analysis (EA). Rheology experiments, including dynamic mechanical thermal analysis (DMTA), frequency sweeps, stress relaxation and time–temperature superposition were conducted to study the stimuli-responsive mechanical properties. Hereby, the activation energy determined by stress relaxation as a combination of the metal complex and the polymer matrix could be determined. Additionally, computational master curves were obtained and the resulting relaxation spectra were analyzed. Beside the macroscopic material properties, temperature-dependent Raman spectroscopy and density functional theory (DFT) calculations were utilized to gain information on the changes on the molecular level. In this context, morphological changes in the polymer matrix were observed, which might be correlated to the presence of supramolecular aggregates. The changes on the molecular level could be linked to the macroscopic properties.
    Universitätsbibliographie Jena:
    fsu_mods_00035445Externer Link

  8. Emergence of nonclassical radiation in strongly laser-driven quantum systems

    Autoren I. Gonoskov, C. Hünecke, S. Gräfe ErscheinungsjahrStatusPrüfung ausstehendErschienen in:New Journal of Physics
    We present an analytical framework for the emergence of nonclassical radiation in strongly laser-driven quantum systems, with a focus on high-order harmonic generation (HHG). Starting from a Pauli–Fierz description, we employ a parametric factorization of the coupled light–matter wavefunction that reduces the dynamics to coupled equations for a field-driven electronic state and a quantized light mode. Within this framework, we identify a simple and predictive mechanism for nonclassicality: it originates from the nonlinear dependence of the electronic dipole response on the light-mode coordinate. An approximately constant dipole yields coherent radiation, a linear dependence produces squeezing, and higher-order nonlinearities give rise to Wigner-function negativity. We illustrate this mechanism for atomic and molecular model systems and analyze its scaling in multi-emitter configurations, indicating routes toward high-photon-number nonclassical radiation in HHG. Our results provide a transparent connection between strong-field dynamics and quantum-optical properties of emitted light, offering a basis for engineering nonclassical states in intense laser–matter interactions.
    Universitätsbibliographie Jena:
    fsu_mods_00044443Externer Link

  9. Time-resolved spectroscopy of a photoactive dinuclear W/Ru complex: spectroscopic evidence for a metastable intermediate with side-on coordinated carbonyl ligand

    Autoren J. Borter, S. Kangsa Banik, K. Kunze, S. Kupfer, D. Schwarzer, W. Seidel ErscheinungsjahrErschienen in:Chemical science
    The photo-induced dynamics of a redox-active dinuclear W(ii)/Ru(ii) complex, [Tp*W(CO)Br(PyC 00000000000000000 00000000000000000 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 00000000000000000 00000000000000000 CCH ₂ )–Ru(bpy) ₂ ](PF ₆ ) (2-PF ₆ ), is revealed by femtosecond infrared and UV-vis pump-probe spectroscopy in combination with quantum chemical calculations. The use of the mononuclear tungsten alkyne complex [Tp*W(CO)Br(PyCCCH ₃ )] (1) as a benchmark allowed an in-depth analysis of the excited state kinetics of 2-PF ₆ . Excitation of the dinuclear complex at 400 nm produces predominantly a triplet metal-to-ligand charge transfer state localised at the Ru(bpy) ₂ chromophore ( ³ MLCT bpy ) with a lifetime of 6 ps. The following transformation into a tungsten-centered triplet state ( ³ MC W ) is accompanied by significant charge transfer and rearrangement of the W–C–O geometry. Subsequent intersysten crossing back to the ground state on a timescale of 12 ps produces a vibrationally excited molecule with up to 3 quanta in the CO stretching vibration. A minor fraction of 10% of the population reacts to an intermediate exhibiting a lifetime of 140 ps and a CO stretching frequency of 1703 cm −¹ . Our quantum chemical calculations disclose that this species corresponds to an isomer trapped in a metastable state of the S ₀ potential surface, with the CO bound side-on to the W centre.
    Universitätsbibliographie Jena:
    fsu_mods_00035844Externer Link

  10. {Mo2} can do it too: dynamic irradiation increases photonic efficiency of light-driven hydrogen evolution by [Mo ₂ S ₁₂ ] ²−

    Autoren S. Kolbinger, K. Krauchanka, D. Kowalczyk, L. Bardong, L. Senz, S. Kupfer, D. Ziegenbalg, C. Streb ErscheinungsjahrErschienen in:Sustainable Energy and Fuels
    Molecular thiomolybdate clusters are promising earth-abundant catalysts for light-driven hydrogen evolution, yet their performance can strongly depend on irradiation conditions. Here we assess dynamically modulated irradiation for homogeneous photocatalytic hydrogen evolution reaction (HER) using [Mo ₂ S ₁₂ ] ²− ({Mo2}) with [Ru(bpy) ₃ ] ²⁺ and ascorbic acid/ascorbate in methanol irradiated using a 465 nm LED. A Design of Experiments (DoE) approach quantifies the effects of LED current, on/off frequency, and duty cycle. Duty cycle and current dominate turnover, with major interactions involving duty cycle. DoE predicts an optimum at 700 mA, 2 Hz and 75% duty cycle, giving a unchanged normalized turnover number (TON, 1.04 ± 0.09) while reducing energy input by 25% vs. static irradiation. Normalized photonic efficiency is maximized at lower average photon input (500 mA, 2 Hz, 25% duty cycle). Time-resolved UV-vis spectroscopy and TD-DFT calculations indicate slow ligand exchange under light exclusion and a distinct photoinduced evolution under irradiation. While the decay kinetics are similar under static and dynamic conditions, dynamic irradiation improves energy and photon utilization, highlighting photonic engineering as a practical lever to optimize molecular photocatalytic HER.
    Universitätsbibliographie Jena:
    fsu_mods_00039354Externer Link

  11. Synthesis and Characterization of a β-Thio-δ-Diimine (BTDDI) and the Related Bimetallic Dimethylaluminium(III) Compound

    Autoren J. Kowalke, T. Rathsack, T. Rüffer, S. Kupfer, R. Kretschmer ErscheinungsjahrErschienen in:Zeitschrift für anorganische und allgemeine Chemie
    Thionation of the β-oxo-δ-diimine (BODDI) 3 with P ₂ S ₅ ·2Py affords the ditopic β-thio-δ-diimine (BTDDI) 4. Based on ¹ H NMR spectroscopy and single-crystal X-ray diffraction, 4 is best described as a bis(β-enamine)-thione in both solution and the solid state. Furthermore, 4 features a thermochromic behavior in solution (c > 2 mmol l −¹ ) and as a solid. Reaction with trimethyl aluminium readily affords the bimetallic dimethylaluminium BTDDI complex 5. In contrast to its oxygen relative, 5 is only weakly emissive and the emission is significantly red-shifted. Scalar-relativistic time-dependent density functional theory calculations suggest that introduction of the sulfur atom promotes an intersystem crossing pathway (∼1 ns) to low-lying and non-emissive triplet states, which competes with fluorescence (∼5 ns).
    Universitätsbibliographie Jena:
    fsu_mods_00035653Externer Link

  12. 4CzIPN Photosensitizes the Cobaloxime-Catalyzed Light-Driven Hydrogen Evolution Reaction

    Autoren A. Tombrink, B. Callies, S. Kupfer, D. Kowalcyk, B. Wiedemann, D. Ziegenbalg, K. Peneva, B. Esser ErscheinungsjahrErschienen in:ChemSusChem :: chemistry & sustainability, energy & materials
    Thermally activated delayed fluorescence (TADF) compounds have found great application as photocatalysts in recent years. Their use as photosensitizers (PS), however, is still limited although they have huge potential as abundant alternatives to traditional noble metal-based PSs, such as [Ru(bpy) ₃ ] ²⁺ . We herein investigate the TADF compound 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as a PS together with the catalyst cobaloxime (Co(dmgH) ₂ (py)Cl) in the photochemical hydrogen evolution reaction (HER). Systematic optimization of the solvent composition, 4CzIPN and catalyst concentration, and sacrificial electron donor (SED) identified ammonium ascorbate as the most effective SED under the conditions tested. Under optimized conditions, the system reached a TON of 6451 ± 82 after 20 h irradiation. Stern–Volmer quenching experiments and scalar-relativistic quantum-chemical calculations provided rate constants for the different processes in the photosensitization mechanism, demonstrating that the quenching of the excited singlet state (S ₁ ) of 4CzIPN by ammonium ascorbate is by far more dominant than the quenching of its excited triplet state (T ₁ ). This work demonstrates that 4CzIPN can sensitize the cobaloxime-catalyzed light-driven HER with ammonium ascorbate as the SED and provides mechanistic insight into the role of singlet- and triplet-state quenching in TADF photosensitization.
    Universitätsbibliographie Jena:
    fsu_mods_00039346Externer Link
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