Teilbibliothek Naturwissenschaften: Chemie

Publikationen

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

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

    Autoren
    M. Thümmler, A. Croy, U. Peschel, S. Gräfe
    Erscheinungsjahr
    Erschienen 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

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

    Autoren
    M. Thümmler, T. Lettau, A. Croy, U. Peschel, S. Gräfe
    Erscheinungsjahr
    Erschienen 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

  4. 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
    Erscheinungsjahr
    Erschienen 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

  5. 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
    Erscheinungsjahr
    Erschienen 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

  6. 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
    Erscheinungsjahr
    Erschienen 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

  7. 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
    Erscheinungsjahr
    Erschienen 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

  8. Hot-Carrier Injection and Millisecond Charge Separation from a Robust Heteroleptic Iron(II) Chromophore Immobilized on TiO2

    Autoren
    T. Whittemore, M. Schmalle, E. Ryndin, M. Spitler, E. Brohmer, S. Rau, L. Zedler, E. Danilov, F. Castellano, S. Kupfer, G. Meyer, D. Sorsche
    Erscheinungsjahr
    Erschienen in:
    Journal of the American Chemical Society
    The synthesis, spectroscopic characterization, computational analysis, and photoelectrochemical behavior of a new iron-based chromophore, [(Cpy) ₂ Fe(deeb)](PF ₆ ) ₂ (Fe(Cpy) ₂ (deeb)), where Cpy is 1-methyl-3-(2-pyridyl)imidazole and deeb is 4,4’-(CO ₂ CH ₂ CH ₃ ) ₂ -2,2’-bipyridine, is reported. Electrochemically reversible waves assigned to a metal-centered E o (Fe III/II ) = +0.48 and a ligand-centered E o (Fe ²⁺/⁺ ) = −1.47 V vs Fc ⁺/⁰ reduction were evident in cyclic voltammetry measurements. The combination of a strong σ-donor and a π-acceptor lowered the energy of the metal-to-ligand charge-transfer (MLCT) excited state relative to the metal-centered state. Two MLCT transitions appear in the visible region at 424 and 580 nm. TDDFT calculations revealed that the lower-energy band was well formulated as Fe(II)→deeb, and the higher-energy transition was charge transfer to both the deeb and Cpy ligands. Resonance Raman spectroscopy supports these findings showing enhanced deeb vibrational modes with 532 nm excitation, both deeb and Cpy modes with 473 nm excitation, and exclusively Cpy with 405 nm excitation. Ultrafast spectroscopy reveals a short-lived (∼2 ps) MLCT excited state and a longer-lived (∼20 ps) metal-centered state. Efficient methods to deprotect the ester groups and anchor the complex to mesoporous TiO ₂ (anatase) thin films in high surface coverages, Fe(Cpy) ₂ (dcb)|TiO ₂ σ = 3 × 10 –⁸ mol/cm ² , were established. Pulsed light excitation of Fe(Cpy) ₂ (dcb)|TiO ₂ resulted in rapid excited state injection (k inj > 10 ⁸ s –¹ ) and formation of a charge-separated state, Fe III (Cpy) ₂ (dcb)|TiO ₂ (e), which persists on the millisecond time scale before returning cleanly to the ground state with second-order kinetics. Injection yields measured 50 ns after light excitation were found to double from Φ = 0.15 with green (532 nm) light to 0.30 with blue (457 nm) light excitation. Incident photon-to-current efficiency (% IPCE) measurements as a function of excitation wavelength in a 0.5 M LiI/I ₂ /CH ₃ CN electrolyte provide clear evidence for band-selective “hot carrier” injection from the remote Cpy-localized excited state. Collectively, the spectroscopic and photoelectrochemical data indicate that a semiconductor can intercept hot electrons from iron chromophores even when the excited-state dipole is oriented away from the surface-anchoring ligand.
    Universitätsbibliographie Jena:
    fsu_mods_00036374Externer Link

  9. Unraveling Charging and Discharging Processes in Organic Radical-Based Electrodes : A Hierarchical Molecular and Quantum Mechanical Approach

    Autoren
    C. Zens, G. Shillito, C. Friebe, S. Kupfer
    Erscheinungsjahr
    Erschienen in:
    ChemSusChem :: chemistry & sustainability, energy & materials
    Organic batteries represent a promising class of energy storage materials, due to their mechanical flexibility and sustainability. Typically, stable radicals, lacking intrinsic conductivity, are utilized as redox-active materials. A recently introduced strategy to overcome this shortcoming is to incorporate stable radicals, i.e., (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), into a polythiophene backbone. Thereby, an electrode material was obtained which does not require conductive additives. The current computational study aims to elucidate the functionality of this material by drawing in-depth structure–property relationships utilizing a hierarchical molecular and quantum mechanical approach. Initially, structural properties of the electrode material's macroenvironment—containing the functionalized polythiophene, electrolyte, and solvent—were assessed in various charging states by molecular dynamics simulations. Subsequently, electronic properties were investigated by time-dependent density functional theory for 564 microenvironments. Via this computational setup, the electronic communication within the material was assessed along intrastrand and interstrand CT processes involving the respective TEMPO and polythiophene units. Thereby, our hierarchical computational approach reveals that the intrinsic conductivity and charge storage capacity of the electrode material stems from efficient intrastrand TEMPO-polythiophene CT processes along short and rigid amid linkers. These insights help to tailor improved conductive organic electrode materials with higher charging and discharging rate capabilities.
    Universitätsbibliographie Jena:
    fsu_mods_00034972Externer Link

  10. A donor–acceptor photosensitizer-catalyst dyad for light-driven nicotinamide hydrogenation

    Autoren
    A. Tombrink, M. Semwal, T. Maisuradze, A. Mengele, D. Straub, A. Kuehne, S. Rau, S. Kupfer, B. Dietzek-Ivanšić, B. Esser
    Erscheinungsjahr
    Erschienen in:
    Chemical science
    Using light energy to drive chemical transformations is of great relevance, with photosynthesis in nature as a grand example. In artificial light-driven catalysis, part of nature's complex supramolecular architecture can be mimicked through the so-called covalently linked photosensitizer-catalyst (PS-CAT) dyads. We herein report a dyad using an organic donor–acceptor PS, with dipyridophenazine as the acceptor and tert-butylcarbazole as the donor (2 t BuCzDPPZ), that contains a coordination site for a rhodium(iii)Cp* center as the catalyst. The organic PS shows a charge-transfer transition upon visible-light irradiation and has redox properties similar to typically used ruthenium-based PSs. The resulting PS-CAT dyad 2 t BuCzDPPZRhCp* shows – with methoxy-substituted 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH-OMe) as the sacrificial electron donor – photocatalytic activity in light-driven NAD ⁺ reduction with a TON of 3.2 (after 4 h). Femtosecond transient absorption and resonance Raman spectroscopy, as well as time-dependent density functional theory (TDDFT) calculations, shed light on the photophysical properties of the PS and PS-CAT dyad and reveal a high dependency of the photoluminescence quantum yield and excited state properties on solvent polarity – in line with its donor–acceptor structure. This work presents a new design concept for PS-CAT dyads in artificial light-driven catalysis and provides important insight into the interplay between solvation dynamics of organic donor–acceptor systems and their photophysics, paving the way for future design strategies.
    Universitätsbibliographie Jena:
    fsu_mods_00034669Externer Link

  11. Light-driven hydrogen evolution reactivity of molecular thio-oxomolybdate catalysts

    Autoren
    L. Schleicher, S. Kolbinger, A. Edwards, K. Sellmann, L. Senz, S. Kupfer, M. Schmitt, J. Popp, C. Streb
    Erscheinungsjahr
    Erschienen in:
    Sustainable Energy and Fuels
    Heterogeneous molybdenum sulfides are widely used noble metal-free hydrogen evolution reaction (HER) catalysts. Thiomolybdates, their molecular analogues have been developed as viable minimal models to study reactivity at the molecular level. Here, we explore the light-driven HER reactivity and stability of the mixed thio-oxo-molybdate prototype [Mo ₂ O ₂ S ₆ ] ²− in homogeneous solution. In combination with the photosensitizer [Ru(bpy) ₃ ] ²⁺ , [Mo ₂ O ₂ S ₆ ] ²− shows promising HER performance (turnover number TON > 500), as well as strong reactivity dependence on the reaction conditions. Mechanistic experimental studies combined with density functional theory computations reveal complex speciation of the catalyst in solution, as well as light-induced and light-independent reaction pathways for catalyst and photosensitizer which are in line with disulfide-for-solvent ligand exchange reactions. These structure–reactivity insights outline design rules for more robust, solvent-tolerant thiomolybdate HER catalysts.
    Universitätsbibliographie Jena:
    fsu_mods_00035842Externer Link

  12. Zandpack: A general tool for time-dependent transportsimulation of nanoelectronics

    Autoren
    A. Bach Lorentzen, A. Croy, A. Jauho, M. Brandbyge
    Erscheinungsjahr
    Erschienen in:
    Computer physics communications: an international journal devoted to computational physics and computer programs in physics
    The auxiliary mode approach to time-dependent open quantum system calculations is implemented and refined to yield a feasible computational approach to simulate nanostructures far from equilibrium. It is done by a careful diagonalization of the electrode level-width function, and provides an efficient approach which can simulate large, open systems at the level of time-dependent density functional theory. The approach, as given in this work, is implemented in the new open-source code Zandpack. The framework is applied to three systems perturbed by the same THz electromagnetic field pulse-form: 1) A Hubbard model for hydrogen on graphene is used to calculate spin-currents, mutual information, spin-transitions, and a pump-probe setup. 2) An armchair graphene nanoribbon (AGNR) probed by a metal tip showing electrons excited from the valence band of the AGNR into the tip via electron-electron interactions. 3) A gold break-junction is modeled with various gap distances, and displays behavior that is more different from the adiabatic case as the gap widens. In the examples 2 and 3, we develop and use a general linearization scheme for time-dependent open system calculations, which utilizes the DFTB+or SIESTAcodes. Program summary Program Title: Zandpack CPC Library link to program files: (to be added by Technical Editor) Developer's repository link: https://github.com/AleksBL Licensing provisions: MPL-2.0 Programming language: Python Nature of problem: Simulating the evolution of electrons in a device region connected to electrodes that are experiencing a time-dependent and strong bias, while at the same time describing the evolving device electrons accurately at the mean-field level. The electronic structure of the electrodes must also be described accurately in terms of the energy-dependence of its level-width function. This on a practical level requires fitting a set of known functions to a sum of Lorentzians. This fit then fixes the parameters of a coupled system of ODEs, in which the electronic density and Hamiltonian appears. Lastly, this system of ODEs has to be solved numerically. Solution method: A user-friendly routine for fitting the electrode level-width functions is implemented. It can either take input from TBtrans or custom user input and convert it to a sum of Lorentzians. We employ the auxiliary mode expansion (AME) method following Popescu and Croy [New J. Phys. 18, 093,944 (2016)] with a modified version of the diagonalization technique, combined with an effective account for the electrode level-width functions. The code can obtain the initial steady state, and propagate this initial steady state after application of a user-defined voltage bias-pulse applied to the electrodes using an explicit Runge-Kutta solver. Throughout this propagation, a user-defined density-dependence is needed, e.g. by interfacing to an external LCAO-DFT code. Such an interface is available for SIESTA and DFTB+, but can also be written by the user. Additional comments including restrictions and unusual features: The AME method does not have any restrictions on how fast oscillations can be, meaning it is valid for slow (e.g. THz fields) as well as fast (e.g. optical fields) perturbations. Simulations with normal-superconducting-normal type setups are also possible. In the current implementation, phonons cannot be included in the calculation, but the method does in theory allow for such [Y. Zhang, C. Y. Yam, G. Chen, J. Chem. Phys. 138 (16) (2013)].
    Universitätsbibliographie Jena:
    fsu_mods_00034615Externer Link
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