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68 Publications visible to you, out of a total of 68
Directionality and the Role of Polarization in Electric Field Effects on Radical Stability

Abstract (Expand)

ccurate quantum-chemical calculations are used to analyze the effects of charges on the kinetics and thermodynamics of radical reactions, with specific attention given to the origin and directionality … of the effects. Conventionally, large effects of the charges are expected to occur in systems with pronounced charge-separated resonance contributors. The nature (stabilization or destabilization) and magnitude of these effects thus depend on the orientation of the interacting multipoles. However, we show that a significant component of the stabilizing effects of the external electric field is largely independent of the orientation of external electric field (e.g. a charged functional group, a point charge, or an electrode) and occurs even in the absence of any pre-existing charge separation. This effect arises from polarization of the electron density of the molecule induced by the electric field. This polarization effect is greater for highly delocalized species such as resonance-stabilized radicals and transition states of radical reactions. We show that this effect on the stability of such species is preserved in chemical reaction energies, leading to lower bond-dissociation energies and barrier heights. Finally, our simplified modelling of the diol dehydratase-catalyzed 1,2-hydroxyl shift indicates that such stabilizing polarization is likely to contribute to the catalytic activity of enzymes.

Authors: Ganna Gryn'ova, Michelle L. Coote

Date Published: 2017

Publication Type: Journal

Charge Transport in Highly Ordered Organic Nanofibrils: Lessons from Modelling

Abstract (Expand)

H-Aggregates featuring tight π-stacks of the conjugated heterocyclic cores represent ideal morphologies for 1D organic semiconductors. Such nanofibrils have larger electronic couplings between the … adjacent cores compared to the herringbone crystal or amorphous assemblies. In this work, we show that for a set of seven structurally and electronically distinct cores, including quaterthiophene and oligothienoacenes, the co-planar dimer model captures the impact of the monomer's electronic structure on charge transport, but more advanced multiscale modelling, featuring molecular dynamics and kinetic Monte-Carlo simulations, is needed to account for the packing and disorder effects. The differences in the results between these two computational approaches arise from the sensitivity of the electronic coupling strength to the relative alignment of adjacent cores, in particular the long-axis shift between them, imposed by the oligopeptide side chains. Our results demonstrate the dependence of the performance of H-aggregates on the chemical nature of the cores and the presence of the side chains, as well as the limitations in using the simple dimer model for a rapid computational pre-screening of the conjugated cores.

Authors: Ganna Gryn’ova, Adrien Nicolaï, Antonio Prlj, Pauline Ollitrault, Denis Andrienko, Clemence Corminboeuf

Date Published: 2017

Publication Type: Journal

Implications of Charge Penetration for Heteroatom-Containing Organic Semiconductors

Abstract (Expand)

The noncovalent interactions of neutral π-conjugated cores, pertinent to organic semiconductor materials, are intimately related to their charge transport properties and involve a subtle interplay of … dispersion, Pauli repulsion, and electrostatic contributions. Realizing structural arrangements that are both energetically preferred and sufficiently conductive is a challenge. We tackle this problem by means of charge penetration contribution to the interaction energy, boosted in systems containing large heteroatoms (e.g., sulfur, selenium, phosphorus, silicon, and arsenic). We find that in both the model and “realistic” dimers of such heteroatom-containing cores dispersion is balanced out by the exchange and interaction energy is instead governed by substantial charge penetration. These systems also feature stronger electronic couplings compared to the dispersion-driven dimers of oligoacenes and/or the herringbone assemblies. Thus, charge penetration, enhanced in the π-conjugated cores comprising larger heteroatoms, arises as an attractive strategy toward potentially more stable and efficient organic electronic materials.

Authors: Ganna Gryn’ova, Clemence Corminboeuf

Date Published: 23rd Nov 2016

Publication Type: Journal

Entropy-Driven Selectivity for Chain Scission: Where Macromolecules Cleave

Abstract (Expand)

We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches … have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high‐temperature (HT) NMR spectroscopy of self‐assembled supramolecular diblock systems as well as temperature‐dependent size‐exclusion chromatography (TD SEC) of covalently bonded Diels–Alder step‐growth polymers.

Authors: Kai Pahnke, Josef Brandt, Ganna Gryn'ova, Ching Y. Lin, Ozcan Altintas, Friedrich G. Schmidt, Albena Lederer, Michelle L. Coote, Christopher Barner-Kowollik

Date Published: 22nd Jan 2016

Publication Type: Journal

Why Are sec-Alkylperoxyl Bimolecular Self-Reactions Orders of Magnitude Faster than the Analogous Reactions of tert-Alkylperoxyls? The Unanticipated Role of CH Hydrogen Bond Donation

Abstract (Expand)

High-level ab initio calculations are used to identify the mechanism of secondary (and primary) alkylperoxyl radical termination and explain why their reactions are much faster than their tertiary … counterparts. Contrary to existing literature, the decomposition of both tertiary and non-tertiary tetroxides follows the same asymmetric two-step bond cleavage pathway to form a caged intermediate of overall singlet multiplicity comprising triplet oxygen and two alkoxyl radicals. The alpha hydrogen atoms of non-tertiary species facilitate this process by forming unexpected CH⋯O hydrogen bonds to the evolving O2. For non-tertiary peroxyls, subsequent alpha hydrogen atom transfer then yields the experimentally observed non-radical products, ketone, alcohol and O2, whereas for tertiary species, this reaction is precluded and cage escape of the (unpaired) alkoxyl radicals is a likely outcome with important consequences for autoxidation.

Authors: Richmond Lee, Ganna Gryn'ova, K. U. Ingold, Michelle L. Coote

Date Published: 2016

Publication Type: Journal

Theory and Practice of Uncommon Molecular Electronic Configurations

Abstract (Expand)

The electronic configuration of the molecule is the foundation of its structure and reactivity. The spin state is one of the key characteristics arising from the ordering of electrons within the … molecule's set of orbitals. Organic molecules that have open‐shell ground states and interesting physicochemical properties, particularly those influencing their spin alignment, are of immense interest within the up‐and‐coming field of molecular electronics. In this advanced review, we scrutinize various qualitative rules of orbital occupation and spin alignment, viz., the aufbau principle, Hund's multiplicity rule, and dynamic spin polarization concept, through the prism of quantum mechanics. While such rules hold in selected simple cases, in general the spin state of a system depends on a combination of electronic factors that include Coulomb and Pauli repulsion, nuclear attraction, kinetic energy, orbital relaxation, and static correlation. A number of fascinating chemical systems with spin states that fluctuate between triplet and open‐shell singlet, and are responsive to irradiation, pH, and other external stimuli, are highlighted. In addition, we outline a range of organic molecules with intriguing non‐aufbau orbital configurations. In such quasi‐closed‐shell systems, the singly occupied molecular orbital (SOMO) is energetically lower than one or more doubly occupied orbitals. As a result, the SOMO is not affected by electron attachment to or removal from the molecule, and the products of such redox processes are polyradicals. These peculiar species possess attractive conductive and magnetic properties, and a number of them that have already been developed into molecular electronics applications are highlighted in this review.

Authors: Ganna Gryn'ova, Michelle L. Coote, Clemence Corminboeuf

Date Published: 1st Nov 2015

Publication Type: Journal

Chemical Shift and Coupling Constant Analysis of Dibenzyloxy Disulfides

Abstract (Expand)

Dialkoxy disulfides have found applications in the realm of organic synthesis as an S2 or alkoxy donor, under thermal and photolytic decompositions conditions, respectively. Spectrally, dibenzyloxy … disulfides possess an ABq in the 1H NMR, which can shift by over 1.1 ppm depending on the substituents present on the aromatic ring, as well as the solvent employed. The effect of the said substituents and solvent were analyzed and compared to the center of the ABq, geminal coupling, and the differences in chemical shifts of the individual doublets. Additionally, quantum-chemical calculations demonstrated the intramolecular H-bonding arrangement, found within the dibenzyloxy disulfides.

Authors: Eric G. Stoutenburg, Ganna Gryn’ova, Michelle L. Coote, Ronny Priefer

Date Published: 1st Feb 2015

Publication Type: Journal

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