Filter and export

Publications

What is a Publication?
66 Publications visible to you, out of a total of 66
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

Experimental Evidence for Competitive N-O and O-C Bond Homolysis in Gas-Phase Alkoxyamines

Abstract (Expand)

The extensive use of alkoxyamines in controlled radical polymerisation and polymer stabilisation is based on rapid cycling between the alkoxyamine (R1R2NOR3) and a stable nitroxyl radical (R1R2NO•) via … homolysis of the labile OC bond. Competing homolysis of the alkoxyamine NO bond has been predicted to occur for some substituents leading to production of aminyl and alkoxyl radicals. This intrinsic competition between the OC and NO bond homolysis processes has to this point been difficult to probe experimentally. Herein we examine the effect of local molecular structure on the competition between NO and OC bond cleavage in the gas phase by variable energy tandem mass spectrometry in a triple quadrupole mass spectrometer. A suite of cyclic alkoxyamines with remote carboxylic acid moieties (HOOCR1R2NOR3) were synthesised and subjected to negative ion electrospray ionisation to yield [M − H]− anions where the charge is remote from the alkoxyamine moiety. Collision-induced dissociation of these anions yield product ions resulting, almost exclusively, from homolysis of OC and/or NO bonds. The relative efficacy of NO and OC bond homolysis was examined for alkoxyamines incorporating different R3 substituents by varying the potential difference applied to the collision cell, and comparing dissociation thresholds of each product ion channel. For most R3 substituents, product ions from homolysis of the OC bond are observed and product ions resulting from cleavage of the NO bond are minor or absent. A limited number of examples were encountered however, where NO homolysis is a competitive dissociation pathway because the OC bond is stabilised by adjacent heteroatom(s) (e.g. R3 = CH2F). The dissociation threshold energies were compared for different alkoxyamine substituents (R3) and the relative ordering of these experimentally determined energies is shown to correlate with the bond dissociation free energies, calculated by ab initio methods. Understanding the structure-dependent relationship between these rival processes will assist in the design and selection of alkoxyamine motifs that selectively promote the desirable OC homolysis pathway.

Authors: David L. Marshall, Ganna Gryn'ova, Michelle L. Coote, Philip J. Barker, Stephen J. Blanksby

Date Published: 1st Feb 2015

Publication Type: Journal

Experimental Demonstration of pH-Dependent Electrostatic Catalysis of Radical Reactions

Abstract (Expand)

Time-dependent fluorescence spectroscopy has been used to demonstrate significant pH-dependent electrostatic effects on the kinetics and thermodynamics of hydrogen atom transfer between … 1-hydroxy-2,2,6,6-tetramethyl-4-piperidinecarboxylic acid (4-CT-H) and the profluorescent nitroxide {2,2,6,6-tetramethyl-4-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-1-piperidinyl}oxidanyl radical (PFN) in dichloromethane. This pH switching does not occur when 4-CT-H is replaced with a structurally analogous hydroxylamine that lacks an acid-base group, or when the polarity of the solvent is increased. These findings validate our recent theoretical predictions that electrostatic stabilisation of delocalised radicals is of functional significance in low polarity environments.

Authors: Marta Klinska, Leesa M. Smith, Ganna Gryn'ova, Martin G. Banwell, Michelle L. Coote

Date Published: 2015

Publication Type: Journal

Powered by
 (v.1.14.2)
About HITS Publication SEEK | About HITS-Publication-SEEK | Funding and Programmes | Credits
Copyright © 2008 - 2023 The University of Manchester and HITS gGmbH