Christoph Bannwarth

Christoph Bannwarth
RWTH Aachen University · Institute of Physical Chemistry

Dr. rer. nat.

About

73
Publications
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Introduction
I am a theoretical chemist and interested in the development of computationally efficient methods and algorithms to study large chemical systems. My research mostly focuses on electronic structure theory, semiempirical methods, and multi-level quantum chemical approaches with target areas being photophysical and photochemical processes, electronic circular dichroism, and noncovalent interactions.

Publications

Publications (73)
Article
A visible-light-mediated, enantioselective approach to axially chiral alkenes is described. Starting from a racemic mixture, a major alkene enantiomer is formed due to selective triplet energy transfer from a catalytically active chiral sensitizer. A catalyst loading of 2 mol % was sufficient to guarantee consistently high enantioselectivities and...
Article
Full-text available
Chirality is a molecular property governed by the topography of the potential energy surface (PES). Thermally achiral molecules interconvert rapidly when the interconversion barrier between the two enantiomers is comparable to or lower than the thermal energy, in contrast to thermally stable chiral configurations. In principle, a change in the PES...
Article
Exciplexes of individual electron donor and acceptor molecules are a promising approach to utilizing otherwise non-emissive triplet states in optoelectronic applications. In this work, we synthesize a series of bis(terpyridine)...
Article
Full-text available
Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called “hot exciplexes” that enables access to...
Preprint
Full-text available
Chirality is a fundamental molecular property governed by the topography of the potential energy surface (PES). The barrier height between two enantiomers relative to the thermal energy dictates the timescale for their interconversion (and thus whether this can be observed). Thermally achiral molecules interconvert rapidly when the interconversion...
Article
We present (3+2)‐ and (4+2)‐cycloadditions of donor–acceptor (D–A) cyclopropanes and cyclobutanes with N‐sulfinylamines and a sulfur diimide, along with a one‐pot, two‐step strategy for the formal insertion of HNSO2 into D–A cyclopropanes. These are rare examples of cycloadditions with D–A cyclopropanes and cyclobutanes whereby the 2π component con...
Article
We present (3+2)‐ and (4+2)‐cycloadditions of donor–acceptor (D–A) cyclopropanes and cyclobutanes with N‐sulfinylamines and a sulfur diimide, along with a one‐pot, two‐step strategy for the formal insertion of HNSO2 into D–A cyclopropanes. These are rare examples of cycloadditions with D–A cyclopropanes and cyclobutanes whereby the 2π component con...
Preprint
Rapid reverse intersystem crossing and high color purity are vital characteristics of emitters with thermally activated delayed fluorescence in opto-electronic devices. We present a new approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moietie...
Preprint
Rapid reverse intersystem crossing and high color purity are vital characteristics of emitters with thermally activated delayed fluorescence in opto-electronic devices. We present a new approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moietie...
Article
The photochemical deracemization of 2,4-disubstituted 2,3-butadienamides (allene amides) was investigated both experimentally and theoretically. The reaction was catalyzed by a thioxanthone which is covalently linked to a chiral 1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-one skeleton providing a U-shaped arrangement of the sensitizing unit relative...
Preprint
Rapid reverse intersystem crossing and high color purity are vital characteristics of emitters with thermally activated delayed fluorescence in opto-electronic devices. We present a new approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moietie...
Article
The cover image is based on the Software Focus TeraChem: A graphical processing unit‐accelerated electronic structure package for large‐scale ab initio molecular dynamics by Stefan Seritan et al., https://doi.org/10.1002/wcms.1494.
Article
Azobenzene is one of the most ubiquitous photoswitches in photochemistry and a prototypical model for photoisomerizing systems. Despite this, its wavelength-dependent photochemistry has puzzled researchers for decades. Upon excitation to the higher energy ππ* excited state instead of the dipole-forbidden nπ* state, the quantum yield of isomerizatio...
Article
Full-text available
This review covers a family of atomistic, mostly quantum chemistry (QC) based semiempirical methods for the fast and reasonably accurate description of large molecules in gas and condensed phase. The theory is derived from a density functional (DFT) perturbation expansion of the electron density in fluctuation terms to various orders similar to the...
Article
The study of photoinduced dynamics in chemical systems necessitates accurate and computationally efficient electronic structure methods, especially as the systems of interest grow larger. The linear response hole-hole Tamm-Dancoff approximated (hh-TDA) density functional theory method was recently proposed to satisfy such demands. The N-electron el...
Article
The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field methods neglect much of the dynamic correlat...
Article
TeraChem was born in 2008 with the goal of providing fast on‐the‐fly electronic structure calculations to facilitate ab initio molecular dynamics studies of large biochemical systems such as photoswitchable proteins and multichromophoric antenna complexes. Originally developed for videogaming applications, graphics processing units (GPUs) offered a...
Article
Developed over the past decade, TeraChem is an electronic structure and ab initio molecular dynamics software package designed from the ground up to leverage graphics processing units (GPUs) to perform large-scale ground and excited state quantum chemistry calculations in the gas and the condensed phase. TeraChem’s speed stems from the reformulatio...
Preprint
div> The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field (CASSCF) methods are deficient in the...
Article
Experimentalists working with diradicals are often facing the question of what kind of species among singlet or triplet diradicals or closed-shell molecules are observed. To treat large diradicals with a high density of electronic states, we propose a simplified version of the spin-flip time-dependent density functional theory (SF-TD-DFT) method fo...
Article
The so-called D4 model is presented for the accurate computation of London dispersion interactions in density functional theory approximations (DFT-D4) and generally for atomistic modeling methods. In this successor to the DFT-D3 model, the atomic coordination-dependent dipole polarizabilities are scaled based on atomic partial charges which can be...
Article
An extended semiempirical tight-binding model is presented, which is primarily designed for the fast calculation of structures and noncovalent interaction energies for molecular systems with roughly 1000 atoms. The essential novelty in this so-called GFN2-xTB method is the inclusion of anisotropic second order density fluctuation effects via short-...
Preprint
The D4 model is presented for the accurate computation of London dispersion interactions in density functional theory approximations (DFT-D4) and generally for atomistic modeling methods. In this successor to the DFT-D3 model, the atomic coordination-dependent dipole polarizabilities are scaled based on atomic partial charges which can be taken fro...
Article
Full-text available
Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds¹—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed². Frequently, however, only a single enantiomeric form of a...
Preprint
Full-text available
An extended semiempirical tight-binding model is presented, which is primarily designed for the fast calculation of structures and non-covalent interactions energies for molecular systems with roughly 1000 atoms. The essential novelty in this so-called GFN2-xTB method is the inclusion of anisotropic second order density fluctuation effects via shor...
Article
The extension of the parameter set for an ultra-fast electronic excitation spectra calculation is presented. The semiempirical theory based on a tight-binding approach, called extended tight-binding (xTB) in combination with the simplified Tamm-Dancoff approximation (sTDA) shows remarkable accuracy at very low computational cost for the calculation...
Article
A revised version of the well-established B97-D density functional approximation with general applicability for chemical properties of large systems is proposed. Like B97-D, it is based on Becke’s power-series ansatz from 1997 and is explicitly parametrized by including the standard D3 semi-classical dispersion correction. The orbitals are expanded...
Article
A black-box type procedure is presented for the generation of a molecule-specific, intermolecular potential energy function. The method uses quantum chemical (QC) information from our recently published extended tight-binding semi-empirical scheme (GFN-xTB) and can treat non-covalently bound complexes and aggregates with almost arbitrary chemical s...
Article
Full-text available
We present a composite procedure for the quantum chemical computation of spin-spin coupled 1H-NMR spectra for general, flexible molecules in solution. It is based on four main steps, namely, conformer/rotamer ensemble (CRE) generation by the fast tight-binding method GFN-xTB and a newly developed search algorithm, relative free energy and NMR param...
Article
Full-text available
We present a composite procedure for the quantum chemical computation of spin-spin coupled 1H-NMR spectra for general, flexible molecules in solution. It is based on four main steps, namely, conformer/rotamer ensemble (CRE) generation by the fast tight-binding method GFN-xTB and a newly developed search algorithm, relative free energy and NMR param...
Article
A fully quantum mechanical (QM) treatment to calculate electronic absorption (UV-Vis) and circular dichroism (CD) spectra of typical biomolecules with thousands of atoms is presented. With our highly efficient sTDA-xTB method, spectra averaged along structures from molecular dynamics (MD) simulations can be computed in a reasonable time frame on st...
Article
A new model, termed D4, for the efficient computation of molecular dipole-dipole dispersion coefficients is presented. As in the related, well established D3 scheme, these are obtained as a sum of atom-in-molecule dispersion coefficients over atom pairs. Both models make use of dynamic polarizabilities obtained from first-principles time-dependent...
Article
A new bis(salicylimine) ligand based on the Tröger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordination to zinc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates as proven by XRD analysis and via comparison of experimental ECD-spectra with...
Article
Full-text available
1,5-bis(R)-3,7-bis[2-(pyridine-2′-yl)ethyl)-1,5-diaza-3,7-diphosphacyclooctanes 1 and 2 and their copper(I) complexes 3 and 4 were developed. The butterfly-shaped copper-iodide core and unusual P,N-chelate and P,P-bridged coordination mode of the heterocyclic ligand in the dinuclear complexes 3 and 4 were revealed. Complexes 3 and 4 display emissio...
Article
Metallosupramolecular ChemistryThe synthesis and properties of a supramolecular octanuclear cage exhibiting spin-crossover behavior in solution are demonstrated by A. Lützen and co-workers in their Communication on page 4930 ff.
Article
Metallosupramolekulare ChemieA. Lützen und Mitarbeiter beschreiben in ihrer Zuschrift auf S. 5012 die Synthese und Eigenschaften eines achtkernigen supramolekularen Käfigs mit Spin-Crossover-Verhalten in Lösung.
Article
We propose a novel, special purpose semi-empirical tight binding (TB) method for the calculation of structures, vibrational frequencies, and non-covalent interactions of large molecular systems with 1000 or more atoms. The functional form of the method is related to the self-consistent density functional TB scheme and mostly avoids element-pair spe...
Article
A series of novel supramolecular octanuclear cages has been synthesized and characterized. Employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis-(4-amino- phenyl)porphyrin or 5,10,15,20-tetrakis-(4-aminophenyl)-porphyrin zinc(II), 1H-4-imidazole carbaldehyde and either zinc(II) or iron(II) salts, we were able to prepare O-...
Article
By employing the subcomponent self-assembly approach utilizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or its zinc(II) complex, 1H-4-imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O-symmetric cages having a confined volume of ca. 1300??(3) . The use of iron(II) salts yielded coordination cages in the high-...
Article
Nach dem Ansatz der Subkomponenten-Selbstorganisation lassen sich aus 5,10,15,20-Tetrakis(4-aminophenyl)porphyrin oder dessen Zink(II)-Komplex, 1H-4-Imidazol-carbaldehyd und Zink(II)- oder Eisen(II)-Salzen O-symmetrische Käfige mit einem abgeschlossenen Hohlraum von 1300 Å3 darstellen. Eisen(II)-Salze lieferten Käfigverbindungen, die bei Raumtemper...
Article
Full-text available
We report on the photophysical properties, conjugation, conformational behavior, intra- and intermolecular hydrogen bonds (HBs) of a series of novel fluorophores, consisting of 3-arylquinoxaline and benzimidazole moieties linked by a single CC bond. Computations employing density functional theory (DFT) reveal that conjugation between these moietie...
Article
Full-text available
The regioisomeric formal Mes2PCH2CH2B(C6F5)2 FLP methane splitting products Mes2P(H)CH2CH2B(CH3)(C6F5)2 and Mes2P(CH3)CH2CH2B(H)(C6F5)2 were produced by indirect stepwise reactions. They were stable at 60 °C and were both characterized by X-ray diffraction. A DFT analysis revealed that their formation from the FLP and CH4 would be endergonic by +6....
Article
Metal-free dual singlet-triplet OLED emitters can provide direct insight into spin statistics - spin correlations and spin relaxation phenomena - through a comparison of fluorescence to phosphorescence intensity. Remarkably, such materials can also function at room temperature, exhibiting phosphorescence lifetimes of several milliseconds. Using ele...
Article
The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such tre...
Chapter
Non-covalent interactions (NCIs) are ubiquitous in nature, and the demonstration of their role in transition metal chemistry remains a vivid domain of research. Indeed, a better understanding of the interplay of NCIs with covalent interactions remains critical as it may create the basis for new conceptual frameworks for the engineering of new funct...
Article
Full-text available
The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a...
Article
The aim of the present work is to explain the causes of the observed deviations from sector and helicity rules to determine the absolute configuration of optically active alpha,beta-unsaturated ketones by means of electronic circular dichroism (ECD). To this end, a series of model compounds with common decahydronaphthalene skeleton representing bot...
Article
Mean-field electronic structure methods like Hartree-Fock, semilocal density functional approximations, or semiempirical molecular orbital (MO) theories do not account for long-range electron correlation (London dispersion interaction). Inclusion of these effects is mandatory for realistic calculations on large or condensed chemical systems and for...
Article
The electronic circular dichroism (ECD) spectrum of the recently synthesized [16]helicene and a derivative comprising two triisopropylsilyloxy protection groups was computed by means of the very efficient simplified time-dependent density functional theory (sTD-DFT) approach. Different from many previous ECD studies of helicenes, nonequilibrium str...
Article
Full-text available
A novel type of cyclic P,N-ligands, pyridyl containing phospholanes, has been synthesized in a moderate yield by the reaction of primary phosphines with 1,4-dichlorobutane in a superbasic medium. A series of homo tetranuclear octahedral Cu4I4L2, dinuclear tetrahedral Cu2I2L3, and dinuclear "head-to-tail" Cu2I2L2 luminescent complexes with these lig...
Article
Eleven different derivatives of Tröger's base were synthesized and successfully resolved by (recycling) HPLC on chiral stationary (S,S)-Whelk-O1 or CHIRALPAK IA phase on a (semi-) preparative scale or synthesized in enantiomerically pure form. The absolute configuration was determined by X-ray crystal structure analysis, comparison of the quantum c...
Article
The dienylborane was prepared by regioselective alkyne hydroboration of the conjugated enyne with Piers' borane [HB(C6F5)2]. Its reaction with a series of acetophenone derived enamines resulted in the formation of the strong enamine β-carbon adduct with the borane Lewis acid (). In contrast B-C adduct formation between the dienylborane and a series...
Article
Eleven different derivatives of Tröger's base were synthesized and successfully resolved by (recycling) HPLC on chiral stationary (S,S)-Whelk-O1 or CHIRALPAK IA phase on a (semi-) preparative scale or synthesized in enantiomerically pure form. The absolute configuration was determined by X-ray crystal structure analysis, comparison of the quantum c...
Article
A density functional theory (DFT) based composite electronic structure approach is proposed to efficiently compute structures and interaction energies in large chemical systems. It is based on the well-known and numerically robust Perdew-Burke-Ernzerhoff (PBE) generalized-gradient-approximation in a modified global hybrid functional with a relative...
Article
Full-text available
The technique of low energy (0-30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0-2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and com...
Article
A convenient way to the new class of geminal Mes2PH+/B(C6F5)2H- pairs is presented. It utilizes triflic acid addition to trans-Mes2PCH=CHB(C6F5)2 followed by triflate/hydride exchange. Thermally induced ring-closure gave a phosphonium/boratacyclopropane zwitterion 8 which formed the Mes2PH(CHMe)B(C6F5)2H P/B FLP-H2 product 10 by subsequent treatmen...
Article
In the present work we show that the electronic circular dichroism (ECD) of delocalized π-systems represents a worst case scenario for Tamm-Dancoff approximated (TDA) linear response methods. We mainly consider density functional theory (TDA-DFT) variants together with range-separated hybrids but the conclusions also apply for other functionals as...
Article
State-of-the-art quantum chemical methods have been applied to describe the association of two frustrated Lewis pairs (FLPs), B(C6F5)3/PR3 (1: R=2,4,6-Me3C6H2; 2: R=CMe3), with different steric demands of the base component. Interaction energies are calculated at the dispersion-corrected DFT, MP2 (second-order Møller-Plesset), and DLPNO-CCSD(T) (do...
Article
In Gegenwart eines katalytisch aktiven, chiralen Ruthenium-Porphyrin-Komplexes (1 Mol-%) gehen spirocyclische Oxindole eine enantioselektive Oxygenierungsreaktion ein (neun Beispiele; e.r. bis zu 97:3). Der Katalysator weist einen Lactamring auf, der für die Substratassoziation über Wasserstoffbrücken verantwortlich ist, und verfügt über ein Ruthen...
Article
Spirocyclic oxindoles undergo an enantioselective oxygenation reaction (nine examples; e.r. up to 97:3) upon catalysis by a chiral ruthenium porphyrin complex (1 mol %). The catalyst exhibits a lactam ring, which is responsible for substrate association through hydrogen bonds, and an active ruthenium center, which is in a defined spatial relationsh...
Article
Full-text available
Reliable thermochemical measurements and theoretical predictions for reactions involving large transition metal complexes in which long-range intramolecular London dispersion interactions contribute significantly to their stabilization are still a challenge, particularly for reactions in solution. As an illustrative and chemically important example...
Article
A simplified time-dependent density functional theory approach (sTD-DFT) that allows fast computation of electronic ultraviolet (UV) or circular dichroism (CD) spectra of molecules with 500-1000 atoms is presented. The matrix elements are treated in the same way as in the simplified Tamm-Dancoff approach (sTDA, S. Grimme, J. Chem. Phys., 138 (2013)...
Article
Coordination-driven self-assembly is one of the most powerful strategies to prepare nanometer-sized discrete (supra)molecular assemblies. Herein, we report on the use of two constitutionally isomeric BINOL-based bis(pyridine) ligands for this purpose. Upon coordination to Pd(II) ions these self-assemble into enantiomerically pure endo- and exo-func...
Article
Die koordinationsgetriebene Selbstorganisation ist eine der leistungsf�higsten Strategien zum Aufbau nanometergroßer diskreter (supra-)molekularer Aggregate. Hier berichten wir �ber die Verwendung von zwei konstitutionsisomeren Bis(pyridin)-Liganden auf der Basis von BINOL zu diesem Zweck. Je nach Substitutionsmuster des BINOL-Gerü�sts bilden sich...
Article
It works ether way: Labile adducts of dialkyl ethers with the electrophilic borane B(C6 F5 )3 are shown to scramble HD to H2 and D2 and catalyze the hydrogenation of 1,1-diphenylethylene.
Article
It works ether way: Labile adducts of dialkyl ethers with the electrophilic borane B(C6F5)3 are shown to scramble HD to H2 and D2 and catalyze the hydrogenation of 1,1‐diphenylethylene.
Article
Anion-π interactions in crystals of fluorobenzyl ammonium salts depend on the degree of fluorination at the aromatics.

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