Walter Thiel

Max Planck Institute for Coal Research, Mülheim-on-Ruhr, North Rhine-Westphalia, Germany

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Publications (468)1687.52 Total impact

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    ABSTRACT: Direct arylation (DA) is emerging as a highly promising method to construct inexpensive conjugated materials for large-area electronics from simple and environ-mentally benign building blocks. Here, we show that exclusive α-C−H selectivity is feasible in the DA of π-extended monomers having unsubstituted thiophene or furan units, leading to fully linear materials. Two new naphthalene diimide-based conjugated copolymersP(FuNDIFuF 4) and P(ThNDIThF 4), composed of naphthalene diimide (NDI), furan (Fu) or thiophene (Th), and tetrafluorobenzene (F 4)are synthesized. Insight into structure−function relationships is given by density functional theory (DFT) calculations and variety of experimental techniques, whereby the effect of the heteroatom on the optical, structural, and electronic properties is investigated. The use of furan (Fu) allows for enhanced solubilities, a smaller dihedral angle between NDI and Fu as a result of the smaller size of Fu, and a smaller π−π-stacking distance in the solid state. P(FuNDIFuF 4) also exhibits a more edge-on orientation compared to P(ThNDIThF 4). Despite these advantageous properties of P(FuNDIFuF 4), P(ThNDIThF 4) exhibits the highest electron mobility: ∼1.3 cm 2 /(V s), which is a factor of ∼3 greater than that of P(FuNDIFuF 4). The enhanced OFET performance of P(ThNDIThF 4) is explained by reduced orientational disorder and the formation of a terrace-like thin-film morphology.
    Chemistry of Materials 12/2014; · 8.24 Impact Factor
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    ABSTRACT: We address the performance of the vertical and adiabatic Franck–Condon (VFC/AFC) approaches combined with time-independent or time-dependent (TI/TD) formalisms in simulating the one-photon absorption spectra of three flavin compounds with distinct structural features. Calculations were done in the gas phase and in two solvents (water, benzene) for which experimental reference measurements are available. We utilized the independent mode displaced harmonic oscillator model without or with frequency alteration (IMDHO/IMDHO-FA) and also accounted for Duschinsky mixing effects. In the initial validation on the first excited singlet state of riboflavin, the range-separated functionals, CAM-B3LYP and ωB97xD, showed the best performance, but B3LYP also gave a good compromise between peak positions and spectral topology. Large basis sets were not mandatory to obtain high-quality spectra for the selected systems. The presence of a symmetry plane facilitated the computation of vibrationally broadened spectra, since different FC variants yield similar results and the harmonic approximation holds rather well. Compared with the AFC approach, the VFC approach performed equally well or even better for all three flavins while offering several advantages, such as avoiding error-prone geometry optimization procedures on excited-state surfaces. We also explored the advantages of curvilinear displacements and of a Duschinsky treatment for the AFC spectra in cases when a rotatable group is present on the chromophore. Taken together, our findings indicate that the combination of the VFC approach with the TD formalism and the IMDHO-FA model offers the best overall performance.
    Journal of Chemical Theory and Computation 11/2014; · 5.39 Impact Factor
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    ABSTRACT: Photoswitching of simple photochromic molecules attracts substantial attention because of its possible role in future photon-driven molecular electronics. Here we model the full photoswitching cycle of a minimal photochromic Schiff base - salicylidene methylamine (SMA). We perform semi-empirical non-adiabatic on-the-fly photodynamics simulations at the OM2/MRCI level and thoroughly analyze the structural time evolution and switching efficiency of the system. We also identify and examine in detail the crucial steps in the SMA photochemistry ruled by excited-state intramolecular proton transfer. The results place the investigated model aromatic Schiff base among the promising candidates for novel photoswitching molecular materials. Our study also shows the potential of the semi-empirical multireference photodynamics simulations as a tool for early-stage molecular photo-device design.
    The journal of physical chemistry. B. 10/2014;
  • Daniel Escudero, Walter Thiel
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    ABSTRACT: In this Article, we address the complexity of the emissive processes of a square-planar heteroleptic Pt(II) complex bearing 2-phenylpyridine (ppy) as cyclometalated ligand and an acetylacetonate derivative (dbm) as ancillary ligand. The origins of emission were identified with the help of density functional theory (DFT) and quadratic response (QR) time-dependent (TD)-DFT calculations including spin-orbit coupling (SOC). To unveil the photodeactivation mechanisms, we explored the triplet potential energy surfaces and computed the SOCs and the radiative decay rates (kr) from possible emissive states. We find that emission likely originates from a higher-lying (3)MLCT/(3)LLCT state and not from the Kasha-like (3)MLCT/(3)LCdbm state. The temperature-dependent nonradiative deactivation mechanisms were also elucidated. The active role of metal-centered ((3)MC) triplet excited states is confirmed for these deactivation pathways.
    Inorganic chemistry. 10/2014;
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    ABSTRACT: Quantum-chemical computational methods are benchmarked for their ability to describe conical in- tersections in a series of organic molecules and models of biological chromophores. Reference results for the geometries, relative energies, and branching planes of conical intersections are obtained us- ing ab initio multireference configuration interaction with single and double excitations (MRCISD). They are compared with the results from more approximate methods, namely, the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham method, spin-flip time-dependent den- sity functional theory, and a semiempirical MRCISD approach using an orthogonalization-corrected model. It is demonstrated that these approximate methods reproduce the ab initio reference data very well, with root-mean-square deviations in the optimized geometries of the order of 0.1 Å or less and with reasonable agreement in the computed relative energies. A detailed analysis of the branching plane vectors shows that all currently applied methods yield similar nuclear displacements for escap- ing the strong non-adiabatic coupling region near the conical intersections. Our comparisons support the use of the tested quantum-chemical methods for modeling the photochemistry of large organic and biological systems.
    The Journal of Chemical Physics 09/2014; 141(12):124122. · 3.12 Impact Factor
  • Ganglong Cui, Walter Thiel
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    ABSTRACT: Trajectory-based fewest-switches surface-hopping (FSSH) dynamics simulations have become a popular and reliable theoretical tool to simulate nonadiabatic photophysical and photochemical processes. Most available FSSH methods model internal conversion. We present a generalized trajectory surface-hopping (GTSH) method for simulating both internal conversion and intersystem crossing processes on an equal footing. We consider hops between adiabatic eigenstates of the non-relativistic electronic Hamiltonian (pure spin states), which is appropriate for sufficiently small spin-orbit coupling. This choice allows us to make maximum use of existing electronic structure programs and to minimize the changes to available implementations of the traditional FSSH method. The GTSH method is formulated within the quantum mechanics (QM)/molecular mechanics framework, but can of course also be applied at the pure QM level. The algorithm implemented in the GTSH code is specified step by step. As an initial GTSH application, we report simulations of the nonadiabatic processes in the lowest four electronic states (S0, S1, T1, and T2) of acrolein both in vacuo and in acetonitrile solution, in which the acrolein molecule is treated at the ab initio complete-active-space self-consistent-field level. These dynamics simulations provide detailed mechanistic insight by identifying and characterizing two nonadiabatic routes to the lowest triplet state, namely, direct S1 → T1 hopping as major pathway and sequential S1 → T2 → T1 hopping as minor pathway, with the T2 state acting as a relay state. They illustrate the potential of the GTSH approach to explore photoinduced processes in complex systems, in which intersystem crossing plays an important role.
    The Journal of chemical physics. 09/2014; 141(12):124101.
  • Bora Karasulu, Walter Thiel
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    ABSTRACT: The photophysical properties of a push-pull flavin derivative, roseoflavin (RoF), are investigated in different surroundings at the molecular level, with focus on intra-molecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) and DFT-based multi-reference configuration interaction (DFT/MRCI) are used to compute excited-state energies and one-electron properties of a truncated RoF model, roseolumiflavin (RoLF). Solvent effects are taken into account implicitly by the conductor-like polarizable continuum model and explicitly through a micro-solvation scheme. In the gas phase, the calculations predict no crossing between the lowest locally-excited (LE) and charge-transfer (CT) states upon twisting the dimethylamine donor group relative to the plane of the isoalloxazine acceptor moiety, whereas this crossing is found to be facile in solution (i.e., in water or benzene). Crossing of the LE and CT states facilitates ICT, which is the main cause of the fluorescence quenching and dual fluorescence character experimentally observed for roseoflavin in solution. The barrier for the ICT process is computed to be lower in water than in benzene, consistent with the enhanced ICT rates observed in more polar solvents. We present a detailed study of the molecular mechanism of the photoinduced ICT process in RoLF. For a typical donor-acceptor chromophore, three such mechanisms are discussed in the literature, which differ in the alignment of the donor and acceptor planes, namely planar ICT (PICT), perpendicular-twisted ICT (TICT), and wagging ICT (WICT). Our theoretical results suggest that the TICT mechanism is favored in RoLF.
    The journal of physical chemistry. B. 09/2014;
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    ABSTRACT: It is proposed that xanthophylls, and carotenoids in general, may assist in energy transfer from the chlorophyll Soret band to the Q band. Ground-state (1Ag) and excited-state (1Bu) optimizations of violaxanthin (Vx) and zeaxanthin (Zx) are performed in an environment mimicking the light-harvesting complex II (LHCII), including the closest chlorophyll b molecule (Chl). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) is used in combination with a semi-empirical description to obtain the excited-state geometries, supported by additional DFT/multireference configuration interaction calculations, with and without point charges representing LHCII. In the ground state, Vx and Zx show similar properties. At the 1Bu minimum, the energy of the Zx 1Bu state is below the Chl Q band, in contrast to Vx. Both Vx and Zx may act as acceptors of Soret-state energy; transfer to the Q band seems to be favored for Vx. These findings suggest that carotenoids may generally mediate Soret-to-Q energy flow in LHCII.
    ChemPhysChem 09/2014; · 3.35 Impact Factor
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    ABSTRACT: A joint experimental and computational study on the glucose–fructose conversion in water is reported. The reactivity of different metal catalysts (CrCl3, AlCl3, CuCl2, FeCl3, and MgCl2) was analyzed. Experimentally, CrCl3 and AlCl3 achieved the best glucose conversion rates, CuCl2 and FeCl3 were only mediocre catalysts, and MgCl2 was inactive. To explain these differences in reactivity, DFT calculations were performed for various metal complexes. The computed mechanism consists of two proton transfers and a hydrogen-atom transfer; the latter was the rate-determining step for all catalysts. The computational results were consistent with the experimental findings and rationalized the observed differences in the behavior of the metal catalysts. To be an efficient catalyst, a metal complex should satisfy the following criteria: moderate Brønsted and Lewis acidity (pKa=4–6), coordination with either water or weaker σ donors, energetically low-lying unoccupied orbitals, compact transition-state structures, and the ability for complexation of glucose. Thus, the reactivity of the metal catalysts in water is governed by many factors, not just the Lewis acidity.
    Chemistry 08/2014; · 5.93 Impact Factor
  • Ganglong Cui, Walter Thiel
    Journal of Physical Chemistry Letters 07/2014; · 6.59 Impact Factor
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    ABSTRACT: We report the first X-ray structure of a spiroaminal hydrochloride. The chiral spiroaminal crystallizes as a racemic hydrochloride in the monoclinic space group P21/n and adopts the thermodynamically most stable conformation. Density functional calculations on several spiroaminals were used to establish correlations between trends in conformational energies, steric repulsions, and anomeric effects and to reveal the mechanism of the ring-opening tautomerization reaction. In the unsubstituted and backbone-substituted spiroaminals, the aminal tautomer is thermodynamically preferred. N-Substituted spiroaminals favor the amine/imine form for steric reasons, except for those with bridging N,N′ groups. The tautomerization from the aminal to the amine/imine is endergonic and kinetically hindered in the neutral species but quite facile after protonation. Anomeric effects lower the barriers but are less important than steric factors for relative energies.
    European Journal of Organic Chemistry 07/2014; 2014(25):5476-5486. · 3.34 Impact Factor
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    ABSTRACT: Fluorescence emission of wild-type green fluorescent protein (GFP) is lost in the S65T mutant, but partly recovered in the S65T/H148D double mutant. These experimental findings are rationalized by a combined quantum mechanics/molecular mechanics (QM/MM) study at the QM(CASPT2//CASSCF)/AMBER level. A barrierless excited-state proton transfer, which is exclusively driven by the Asp148 residue introduced in the double mutant, is responsible for the ultrafast formation of the anionic fluorescent state, which can be deactivated through a concerted asynchronous hula-twist photoisomerization. This causes the lower fluorescence quantum yield in S65T/H148D compared to wild-type GFP. Hydrogen out-of-plane motion plays an important role in the deactivation of the S65T/H148D fluorescent state.
    Angewandte Chemie 07/2014;
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    ABSTRACT: Fluorescence emission of wild-type green fluorescent protein (GFP) is lost in the S65T mutant, but partly recovered in the S65T/H148D double mutant. These experimental findings are rationalized by a combined quantum mechanics/molecular mechanics (QM/MM) study at the QM(CASPT2//CASSCF)/AMBER level. A barrierless excited-state proton transfer, which is exclusively driven by the Asp148 residue introduced in the double mutant, is responsible for the ultrafast formation of the anionic fluorescent state, which can be deactivated through a concerted asynchronous hula-twist photoisomerization. This causes the lower fluorescence quantum yield in S65T/H148D compared to wild-type GFP. Hydrogen out-of-plane motion plays an important role in the deactivation of the S65T/H148D fluorescent state.
    Angewandte Chemie International Edition 07/2014; · 11.34 Impact Factor
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    Computational and Theoretical Chemistry 07/2014; · 1.14 Impact Factor
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    ABSTRACT: We report the synthesis of [H2B(pz)2PR]+, [H2C(pz)2PR]+2, [HB(pz)3P]+2, and [HC(pz)3P]+3 (H2B(pz)2=bis(pyrazolyl)borate; H2C(pz)2=bis(pyrazolyl)methane; HB(pz)3=tris(pyrazolyl)borate; HC(pz)3=tris(pyrazolyl) methane; R=Ph, Cy or Et2N) by reaction of the corresponding neutral or anionic ligands with chlorophosphines in the presence of TMSOTf. The structures of these compounds were determined by X‐ray crystallographic analysis and the nature of their bonding was examined using density functional theory. P‐centered (poly)cations stabilized by bis/tris(pyrazolyl)borate/methane ancillary ligands (see figure) can be prepared and structurally analyzed. The highly positive charge at the phosphorous center gives these compounds Lewis acidic character.
    Chemistry 07/2014; 20(28). · 5.83 Impact Factor
  • Daniel Escudero, Walter Thiel
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    ABSTRACT: We report an assessment of the performance of density functional theory-based multireference configuration interaction (DFT/MRCI) calculations for a set of 3d- and 4d-transition metal (TM) complexes. The DFT/MRCI results are compared to published reference data from reliable high-level multi-configurational ab initio studies. The assessment covers the relative energies of different ground-state minima of the highly correlated CrF6 complex, the singlet and triplet electronically excited states of seven typical TM complexes (MnO4 (-), Cr(CO)6, [Fe(CN)6](4-), four larger Fe and Ru complexes), and the corresponding electronic spectra (vertical excitation energies and oscillator strengths). It includes comparisons with results from different flavors of time-dependent DFT (TD-DFT) calculations using pure, hybrid, and long-range corrected functionals. The DFT/MRCI method is found to be superior to the tested TD-DFT approaches and is thus recommended for exploring the excited-state properties of TM complexes.
    The Journal of chemical physics. 05/2014; 140(19):194105.
  • Walter Thiel
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    ABSTRACT: Die exponentiell zunehmende Zahl an Zitationen verdeutlicht das explosive Wachstum der ,,Computational Catalysis“ in den beiden letzten Jahrzehnten. Der Essay skizziert die historische Entwicklung, den jetzigen Stand der Forschung und die zukünftigen Perspektiven auf diesem Gebiet.
    Angewandte Chemie 05/2014;
  • Walter Thiel
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    ABSTRACT: The explosive growth of computational catalysis over the past two decades is reflected by the exponentially increasing number of citations. The Essay traces the historical development, illustrates the current state, and offers comments on the future perspectives of this field.
    Angewandte Chemie International Edition 05/2014; · 11.34 Impact Factor
  • Toru Saito, Walter Thiel
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    ABSTRACT: We report a combined quantum mechanics/molecular mechanics (QM/MM) study on the mechanism of reversible dioxygen binding in the active site of hemocyanin (Hc). The QM region is treated by broken-symmetry density functional theory (DFT) with spin projection corrections. The X-ray structures of deoxygenated (deoxyHc) and oxygenated (oxyHc) hemocyanin are well reproduced by QM/MM geometry optimizations. The computed relative energies strongly depend on the chosen density functional. They are consistent with the available thermodynamic data for oxygen binding in hemocyanin and in synthetic model complexes when using the BH&HLYP hybrid functional with 50% Hartree-Fock exchange. According to the QM(BH&HLYP)/MM results, the reaction proceeds stepwise with two sequential electron transfer (ET) processes in the triplet state followed by an intersystem crossing to the singlet product. The first ET step leads to a non-bridged superoxo CuBII-O2•- intermediate via a low-barrier transition state. The second ET step is even more facile and yields a side-on oxyHc complex with the characteristic Cu2O2 butterfly core, accompanied by triplet-singlet intersystem crossing. The computed barriers are very small so that the two ET processes are expected to very rapid and nearly simultaneous.
    The Journal of Physical Chemistry B 04/2014; · 3.61 Impact Factor
  • Eliot Boulanger, Walter Thiel
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    ABSTRACT: The polarization of the environment can influence the results from hybrid quantum mechanical/molecular mechanical (QM/MM) simulations of enzymatic reactions. In this article, we address several technical aspects in the development of polarizable QM/MM embedding using the Drude Oscillator (DO) force field. We propose a stable and converging update of the DO polarization state for geometry optimizations and a suitable treatment of the QM/MM-DO boundary when the QM and MM regions are separated by cutting through a covalent bond. We assess the performance of our approach by computing binding energies and geometries of three selected complexes relevant to biomolecular modeling, namely the water trimer, the N-methylacetamide dimer, and the cationic bis(benzene)sodium sandwich complex. Using a recently published MM-DO force field for proteins, we evaluate the effect of MM polarization on the QM/MM energy profiles of the enzymatic reactions catalyzed by chorismate mutase and by p-hydroxybenzoate hydroxylase. We find that inclusion of MM polarization affects the computed barriers by about 10%.
    Journal of Chemical Theory and Computation 03/2014; 10(4):1795–1809. · 5.39 Impact Factor

Publication Stats

5k Citations
1,687.52 Total Impact Points

Institutions

  • 2000–2014
    • Max Planck Institute for Coal Research
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
    • San Diego Supercomputer Center
      San Diego, California, United States
  • 2013
    • University College London
      • Department of Physics and Astronomy
      Londinium, England, United Kingdom
    • Beijing Normal University
      Peping, Beijing, China
  • 2012
    • Chinese Academy of Sciences
      Peping, Beijing, China
  • 2010–2012
    • University of Queensland 
      • Australian Institute for Bioengineering and Nanotechnology
      Brisbane, Queensland, Australia
  • 2008–2011
    • ETH Zurich
      • Laboratory of Physical Chemistry
      Zürich, ZH, Switzerland
    • University of Strathclyde
      • Department of Pure and Applied Chemistry
      Glasgow, SCT, United Kingdom
  • 2008–2010
    • Universität Stuttgart
      Stuttgart, Baden-Württemberg, Germany
  • 1994–2010
    • University of Zurich
      • Institut für Organische Chemie
      Zürich, ZH, Switzerland
  • 1987–2010
    • Bergische Universität Wuppertal
      • • Inorganic Chemistry
      • • Physical and Theoretical Chemistry
      • • Department of Chemistry and Biology
      Wuppertal, North Rhine-Westphalia, Germany
  • 2009
    • University of Cologne
      • I. Institute of Physics
      Köln, North Rhine-Westphalia, Germany
    • Industrial University of Santander
      Bucaramanga, Santander, Colombia
    • University of Glasgow
      • School of Chemistry
      Glasgow, SCT, United Kingdom
  • 2008–2009
    • Technische Universität Dresden
      • Physical Chemistry
      Dresden, Saxony, Germany
  • 2004–2009
    • Hebrew University of Jerusalem
      • • Lise Meitner Minerva Center for Computational Quantum Chemistry
      • • Department of Organic Chemistry
      Jerusalem, Jerusalem District, Israel
    • Max Planck Society
      München, Bavaria, Germany
    • Technische Universität Chemnitz
      • Institute of Chemistry
      Karl-Marx-Stadt, Saxony, Germany
    • Athens State University
      Athens, Alabama, United States
  • 2007–2008
    • University of Wuerzburg
      • Institute of Organic Chemistry
      Würzburg, Bavaria, Germany
    • California Pacific University
      Pinole, California, United States
  • 2005
    • University of Bergen
      • Department of Chemistry
      Bergen, Hordaland Fylke, Norway
    • Heinrich-Heine-Universität Düsseldorf
      • Institut für Molekulare Enzymtechnologie (IMET)
      Düsseldorf, North Rhine-Westphalia, Germany
  • 2004–2005
    • University of Minnesota Twin Cities
      • Department of Chemistry
      Minneapolis, MN, United States
  • 2003–2004
    • University of Georgia
      • Center for Computational Chemistry
      Athens, GA, United States
    • École Polytechnique Fédérale de Lausanne
      • Laboratoire de chimie physique moléculaire
      Lausanne, VD, Switzerland
    • Shanxi Normal University
      Saratsi, Shanxi Sheng, China
  • 2000–2004
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Computer-Chemistry-Center
      Erlangen, Bavaria, Germany
  • 2002
    • Universität Heidelberg
      • Interdisciplinary Center for Scientific Computing
      Heidelberg, Baden-Wuerttemberg, Germany
  • 2001
    • Université de Rennes 1
      Roazhon, Brittany, France