123 results on '"E. Stephen Davies"'
Search Results
2. Donor-Acceptor Dyads and Triads Employing Core-Substituted Naphthalene Diimides: A Synthetic and Spectro (Electrochemical) Study
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Samuel Quinn, E. Stephen Davies, Nicholas Pearce, Callum Rosenberg, Constance R. Pfeiffer, Georgia R. F. Orton, and Neil R. Champness
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naphthalene diimide ,phenothiazine ,phenoxazine ,electrochemistry ,spectroelectrochemistry ,Organic chemistry ,QD241-441 - Abstract
Donor-acceptor dyads and triads comprising core-substituted naphthalene diimide (NDI) chromophores and either phenothiazine or phenoxazine donors are described. Synthesis combined with electrochemical and spectroelectrochemical investigations facilitates characterisation of the various redox states of these molecules, confirming the ability to combine arrays of electron donating and accepting moieties into single species that retain the redox properties of these individual moieties.
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- 2022
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3. Thionated Perylene Diimide–Phenothiazine Dyad: Synthesis, Structure, and Electrochemical Studies
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Nicholas Pearce, E. Stephen Davies, William Lewis, and Neil R. Champness
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Chemistry ,QD1-999 - Published
- 2018
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4. Selective reduction and homologation of carbon monoxide by organometallic iron complexes
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Helen R. Sharpe, Ana M. Geer, Laurence J. Taylor, Benjamin M. Gridley, Toby J. Blundell, Alexander J. Blake, E. Stephen Davies, William Lewis, Jonathan McMaster, David Robinson, and Deborah L. Kays
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Science - Abstract
Metal-mediated activation of CO for C-C coupling reactions is a valuable approach to carbon monoxide valorization. Here, the authors use low-coordinate iron(II) complexes for the selective scission and homologation of CO affording unusual squaraines and iron carboxylates under mild conditions.
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- 2018
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5. Influence of Hydrogen-Bonding Interactions on Nuclearity and Structure of Palladium Tiara-like Complexes
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Harry J. Martin, Constance R. Pfeiffer, E. Stephen Davies, Adrienne L. Davis, William Lewis, and Neil R. Champness
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Chemistry ,QD1-999 - Published
- 2018
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6. per-Alkoxy-pillar[5]arenes as Electron Donors: Electrochemical Properties of Dimethoxy-Pillar[5]arene and Its Corresponding Rotaxane
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Nicholas Pearce, E. Stephen Davies, and Neil R. Champness
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pillararene ,rotaxane ,electrochemistry ,voltammetry ,oxidation ,Organic chemistry ,QD241-441 - Abstract
1,4-dimethoxypillar[5]arene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in [2]rotaxanes, suggesting that pillar[5]arenes can be employed as viable, yet unreported, electron donors.
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- 2020
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7. Morpholino-Substituted BODIPY Species: Synthesis, Structure and Electrochemical Studies
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Hawazen Hassanain, E. Stephen Davies, William Lewis, Deborah L. Kays, and Neil R. Champness
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boron-dipyrromethene dye ,halogen bonding ,polymorphism ,hirshfeld surface analysis ,spectroelectrochemistry ,Crystallography ,QD901-999 - Abstract
Functionalization of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) chromophores at the 2,6-positions with iodo substituents and morpholino-substituted α-methyl groups affords molecules with strong absorbance in the visible spectrum. The effect of such substitution on the solid-state arrangements, absorption, fluorescence and electronic properties of these dye molecules is reported. The spectroscopic and spectroelectrochemical measurements display intense absorptions in the UV-visible spectrum with bathochromic shifts, in comparison to unfunctionalized BODIPY, and a positive shift in redox potentials due to functionalisation of the BODIPY core. Halogen bonds are observed in the solid-state structures of both halogenated BODIPY species, which in one case leads to the formation of an unusual halogen bonded framework.
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- 2020
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8. Tuning the interactions between electron spins in fullerene-based triad systems
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Maria A. Lebedeva, Thomas W. Chamberlain, E. Stephen Davies, Bradley E. Thomas, Martin Schröder, and Andrei N. Khlobystov
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carbon nanomaterials ,electrochemistry ,EPR ,fullerene dimers ,fullerene triads ,spin–spin interactions ,Science ,Organic chemistry ,QD241-441 - Abstract
A series of six fullerene–linker–fullerene triads have been prepared by the stepwise addition of the fullerene cages to bridging moieties thus allowing the systematic variation of fullerene cage (C60 or C70) and linker (oxalate, acetate or terephthalate) and enabling precise control over the inter-fullerene separation. The fullerene triads exhibit good solubility in common organic solvents, have linear geometries and are diastereomerically pure. Cyclic voltammetric measurements demonstrate the excellent electron accepting capacity of all triads, with up to 6 electrons taken up per molecule in the potential range between −2.3 and 0.2 V (vs Fc+/Fc). No significant electronic interactions between fullerene cages are observed in the ground state indicating that the individual properties of each C60 or C70 cage are retained within the triads. The electron–electron interactions in the electrochemically generated dianions of these triads, with one electron per fullerene cage were studied by EPR spectroscopy. The nature of electron–electron coupling observed at 77 K can be described as an equilibrium between doublet and triplet state biradicals which depends on the inter-fullerene spacing. The shorter oxalate-bridged triads exhibit stronger spin–spin coupling with triplet character, while in the longer terephthalate-bridged triads the intramolecular spin–spin coupling is significantly reduced.
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- 2014
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9. Self‐assembly of chiral diketopyrrolopyrrole chromophores giving supramolecular chains in monolayers and twisted microtapes
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Joshua Humphreys, C. Elizabeth Killalea, Flavia Pop, E. Stephen Davies, Giuliano Siligardi, and David B. Amabilino
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Pharmacology ,Organic Chemistry ,Drug Discovery ,Spectroscopy ,Catalysis ,Analytical Chemistry - Published
- 2023
10. Host–Guest Chemistry in Boron Nitride Nanotubes: Interactions with Polyoxometalates and Mechanism of Encapsulation
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Jack W. Jordan, Alexander I. Chernov, Graham A. Rance, E. Stephen Davies, Anabel E. Lanterna, Jesum Alves Fernandes, Alexander Grüneis, Quentin Ramasse, Graham N. Newton, and Andrei N. Khlobystov
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Colloid and Surface Chemistry ,General Chemistry ,Biochemistry ,Catalysis - Abstract
Boron nitride nanotubes (BNNTs) are an emerging class of molecular container offering new functionalities and possibilities for studying molecules at the nanoscale. Herein, BNNTs are demonstrated as highly effective nanocontainers for polyoxometalate (POM) molecules. The encapsulation of POMs within BNNTs occurs spontaneously at room temperature from an aqueous solution, leading to the self-assembly of a POM@BNNT host-guest system. Analysis of the interactions between the host-nanotube and guest-molecule indicate that Lewis acid-base interactions between W═O groups of the POM (base) and B-atoms of the BNNT lattice (acid) likely play a major role in driving POM encapsulation, with photoactivated electron transfer from BNNTs to POMs in solution also contributing to the process. The transparent nature of the BNNT nanocontainer allows extensive investigation of the guest-molecules by photoluminescence, Raman, UV-vis absorption, and EPR spectroscopies. These studies revealed considerable energy and electron transfer processes between BNNTs and POMs, likely mediated via defect energy states of the BNNTs and resulting in the quenching of BNNT photoluminescence at room temperature, the emergence of new photoluminescence emissions at cryogenic temperatures (100 K), a photochromic response, and paramagnetic signals from guest-POMs. These phenomena offer a fresh perspective on host-guest interactions at the nanoscale and open pathways for harvesting the functional properties of these hybrid systems.
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- 2022
11. Slow magnetic relaxation in Fe(<scp>ii</scp>) m-terphenyl complexes
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Andrew J. Valentine, Ana M. Geer, Toby J. Blundell, Will Tovey, Matthew J. Cliffe, E. Stephen Davies, Stephen P. Argent, William Lewis, Jonathan McMaster, Laurence J. Taylor, Daniel Reta, Deborah L. Kays, Engineering and Physical Sciences Research Council (UK), University of Nottingham, and Leverhulme Trust
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Inorganic Chemistry ,Jahn Teller distorsion ,family ,spin crossover ,behavior ,ligand field ,anisotropy ,Fe ,single ,electronic structures - Abstract
Two-coordinate transition metal complexes are exciting candidates for single-molecule magnets (SMMs) because their highly axial coordination environments lead to sizeable magnetic anisotropy. We report a series of five structurally related two-coordinate Fe(II) m-terphenyl complexes (4-R-2,6-Xyl2C6H2)2Fe [R = tBu (1), SiMe3 (2), H (3), Cl (4), CF3 (5)] where, by changing the functionalisation of the para-substituent (R), we alter their magnetic function. All five complexes are field-induced single-molecule magnets, with relaxation rates that are well-described by a combination of direct and Raman mechanisms. By using more electron donating R groups we were able to slow the rate of magnetic relaxation. Our ab initio calculations predict a large crystal field splitting (>850 cm−1) and sizeable zero-field splitting parameters (ca. −60 cm−1, |E| < 0.2 cm−1) for 1–5. These favourable magnetic properties suggest that m-terphenyl ligands have untapped potential as chemically versatile ligands able to impose highly axial crystal fields., We acknowledge the EPSRC [grant number EP/R004064/1]; the Leverhulme Trust [grant numbers RPG-2014-317; RF-2021-102]; and the University of Nottingham [Hobday Bequest] for financial support of this research.
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- 2022
12. Highly electron deficient diketopyrrolopyrroles
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Joshua Humphreys, Ferdinando Malagreca, Paul A. Hume, E. Stephen Davies, Stephen P. Argent, Tracey D. Bradshaw, David B. Amabilino, University of Nottingham, Engineering and Physical Sciences Research Council (UK), Ministerio de Ciencia, Innovación y Universidades (España), Humphreys, Joshua, Malagreca, Ferdinando, Hume, Paul A., Argent, Stephen P., Bradshaw, Tracey D., and Amabilino, David B.
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Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
The synthesis, spectroelectrochemical and structural characteristics of highly electron-accepting diketopyrrrolopyrrole (DPP) molecules with adjoining pyridinium rings is reported, along with an assessment of their toxicity, which is apparently low. The compounds show reversible electrochemistry and in one subfamily a massive increase in molar extinction coefficient upon electrochemical reduction., This work was supported by the University of Nottingham through the Beacon of Excellence Propulsion Futures and the EPSRC through the LDMI DTP for funding. The Diamond Light Source Ltd (beamline I19) is thanked for access to collect diffraction data of crystals., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).
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- 2023
13. A Mixed‐Addenda Mo/W Organofunctionalised Hybrid Polyoxometalate
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Sharad S. Amin, Jamie M. Cameron, Max Winslow, E. Stephen Davies, Stephen P. Argent, David Robinson, and Graham N. Newton
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Inorganic Chemistry - Abstract
A mixed-addenda W/Mo hybrid polyoxometalate cluster - K 6 [P 2 W 15 Mo 2 O 61 (POC 6 H 5 ) 2 ] ( 1 ) was synthesized from the condensation of K 10 [P 2 W 15 Mo 2 O 61 ] and phenylphosphonic acid under acidic conditions. Single-crystal X-ray diffraction confirmed the structure of the hybrid cluster and the presence of two Mo centers in the cap of the lacunary cluster. The electronic effects of metal substitution were studied by cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance spectroscopy and supported by density functional theory calculations. Comparing 1 to its tungsten-only analogue K 6 [P 2 W 17 O 61 (POC 6 H 5 ) 2 ] ( 2 ), a more positive potential for the first reduction process was induced by the substitution of W for Mo, consistent with a significant lowering of the cluster LUMO energy.
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- 2022
14. Hydrophosphination of Activated Alkenes by a Cobalt(I) Pincer Complex
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Deborah L. Kays, Ana M. Geer, William Lewis, E. Stephen Davies, Roberto Nolla-Saltiel, Alexander J. Blake, Olivia Churchill, Laurence J. Taylor, Engineering and Physical Sciences Research Council (UK), Leverhulme Trust, Consejo Nacional de Ciencia y Tecnología (México), and University of Nottingham
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Chemistry ,Research council ,Organic Chemistry ,Hydrophosphination ,Library science ,chemistry.chemical_element ,Homogeneous catalysis ,General Chemistry ,Cobalt ,Catalysis ,Engineering and Physical Sciences ,Pincer movement - Abstract
Herein we report the synthesis of three heteroleptic first‐row transition metal(II) complexes containing carbazolido NNN pincer ligands and conversion to the corresponding metal(I)‐carbonyl complexes via a reductive carbonylation route. These complexes are precatalysts for the hydrophosphination of activated alkenes, affording a cobalt‐catalysed hydrophosphination process that solely and selectively yields the β addition (anti‐Markovnikov) product. The scope of this transformation has been investigated using a variety of activated alkenes. Isolation and characterisation of substrate‐coordinated intermediates reveal available coordination sites, which provide insight into the proposed catalytic cycle., This work was supported by the Engineering and Physical Sciences Research Council [grant number EP/R004064/1]; The Leverhulme Trust [grant number RPG‐2014‐317]; CONACYT (Mexican Council for Science and Technology) [grant number CVU 600474] and the University of Nottingham.
- Published
- 2020
15. Influence of molecular design on radical spin multiplicity: characterisation of BODIPY dyad and triad radical anions
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Deborah L. Kays, Michael W. George, Alisdair Wriglesworth, E. Stephen Davies, Neil R. Champness, Magnus W. D. Hanson-Heine, Barry Mangham, William Lewis, Nicholas A. Besley, and Jonathan McMaster
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010405 organic chemistry ,General Physics and Astronomy ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Spectral line ,0104 chemical sciences ,law.invention ,Organic molecules ,chemistry.chemical_compound ,chemistry ,law ,Moiety ,Singlet state ,Physical and Theoretical Chemistry ,Multiplicity (chemistry) ,BODIPY ,Electron paramagnetic resonance ,Spectroscopy - Abstract
A strategy to create organic molecules with high degrees of radical spin multiplicity is reported in which molecular design is correlated with the behaviour of radical anions in a series of BODIPY dyads. Upon reduction of each BODIPY moiety radical anions are formed which are shown to have different spin multiplicities by electron paramagnetic resonance (EPR) spectroscopy and distinct profiles in their cyclic voltammograms and UV-visible spectra. The relationship between structure and multiplicity is demonstrated showing that the balance between singlet, biradical or triplet states in the dyads depends on relative orientation and connectivity of the BODIPY groups. The strategy is applied to the synthesis of a BODIPY triad which adopts an unusual quartet state upon reduction to its radical trianion.
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- 2020
16. Ground and Excited States of Bis‐4‐Methoxybenzyl‐Substituted Diketopyrrolopyrroles: Spectroscopic and Electrochemical Studies
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Alanna S. Murphy, Matthew J. Cliffe, E. Stephen Davies, C. Elizabeth Killalea, Glen J. Murray, Paul A. Hume, William Lewis, Joshua Humphreys, and David B. Amabilino
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chemistry.chemical_classification ,Materials science ,Molecular energy level ,010405 organic chemistry ,General Chemistry ,010402 general chemistry ,Crystal engineering ,Photochemistry ,01 natural sciences ,Fluorescence ,Acceptor ,0104 chemical sciences ,symbols.namesake ,chemistry ,Stokes shift ,Excited state ,symbols ,Molecule ,Alkyl - Abstract
A series of symmetrically bis-4-methoxybenzyl (4MB) N-substituted 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) derivatives have been synthesized. The 4MB unit makes the DPP core soluble, and shows subtle modification of up to 0.2 eV in ground and excited states of the core when compared with related alkyl derivatives. Absorption and emission spectroscopy, as well as electrochemical and computational methods have been employed to prove the importance of the peripheral aryl units on the donor/ acceptor properties of the molecules. The 4MB products are highly fluorescent (quantum yields approaching 100 % in solution), with a unique distribution of frontier states shown by spectroelectrochemistry. The solid-state fluorescence correlates with the X-ray crystal structures of the compounds, a Stokes shift of approximately 80 nm is seen for two of the compounds. The frontier energy levels show that this subtle substitutional change could be of future use in molecular energy level tailoring in these, and related, materials for organic (opto)electronics.
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- 2019
17. Structural characterization and optical properties of two copper(<scp>i</scp>)-iodide BODIPY coordination polymers
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Hawazen Hassanain, Deborah L. Kays, Neil R. Champness, William Lewis, and E. Stephen Davies
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Quenching (fluorescence) ,Ligand ,Coordination polymer ,02 engineering and technology ,General Chemistry ,Chromophore ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Pyridine ,Polymer chemistry ,Molecule ,General Materials Science ,BODIPY ,0210 nano-technology ,Copper(I) iodide - Abstract
Functionalization of boron-dipyrrin (BODIPY) chromophores with pyridine (1) or pyrimidine (2) substituents affords molecules with strong absorbance in the visible spectrum which are also highly fluorescent in solution, in thin films and as powders. Reaction of either 1, a bipyridyl ligand, or 2, a bipyrimidinyl ligand, with CuI in MeCN affords a one-dimensional coordination polymer (3) or a three-dimensional coordination polymer (4), respectively. Although the free ligands, 1 and 2, exhibit fluorescence in the solid-state, metal coordination in the CuI coordination polymers, 3 and 4, leads to quenching despite the retention of the BODIPY core.
- Published
- 2019
18. Photophysical and electrochemical properties of [Re(CO)3Cl(NN)] (NN = dppp3, dppp2, dppp2Br) complexes functionalised with pendant pyridyl ligands
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E. Stephen Davies, Bethany Adams, Katherine E. A. Reynolds, Michael Towrie, Michael W. George, Peter A. Summers, Kam Loon Fow, and Nasiru Ibrahim
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education.field_of_study ,Ligand ,Phenanthroline ,010401 analytical chemistry ,Phenazine ,Heteroatom ,Population ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Excited state ,0210 nano-technology ,Electron paramagnetic resonance ,education ,HOMO/LUMO ,Spectroscopy - Abstract
We report the synthesis, electrochemical, and photophysical properties of a series of rhenium complexes, [Re(CO)3Cl(NN)] (NN = dppp2, dppp3, and dppp2Br; dppp2 = pyrido[2′,3′:5,6]pyrazino[2,3-f][1,10]phenanthroline, dppp3 = pyrido[3′,4′:5,6]pyrazino[2,3-f][1,10]phenanthroline, dppp2Br = 8-bromopyrido[2′,3′:5,6]pyrazino[2,3-f][1,10]phenanthroline), which have potential for use as CO2 photoreduction catalysts. The complexes are related to [Re(CO)3Cl(dppz)] (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) but have an additional nitrogen heteroatom in the distal phenazine (phz) aromatic ring of the dppz ligand which is known to promote potential photoinduced CO2 binding and reduction in related complexes. We use Fourier transform infrared (FTIR), UV/Visible, electron paramagnetic resonance (EPR) and time-resolved infrared (TRIR) spectroscopies to investigate how the location of the additional nitrogen atom, and how the nature of the substituents affects the photophysical properties. In addition, the one electron reduced catalysts are generated following bulk electrochemical reduction and characterised in CH2Cl2. TRIR experiments in d6-DMSO, CH3CN, CH2Cl2, THF and toluene reveal that excitation generates a 3MLCT(phz) (phz = phenazine) excited state in all compounds. In CH3CN and d6-DMSO (not for [Re(CO)3Cl(dppp2)]), we observe the concomitant formation of an 3IL ππ* (IL = intra ligand) excited state. For [Re(CO)3Cl(dppp2)] and [Re(CO)3Cl(dppp3)] in toluene, a mixture of 3MLCT(phen) (phen = phenanthroline) and 3MLCT(phz) states appear to form together, and decay at the same rate. Inclusion of an nitrogen atom in the phz moiety of the dppz ligand lowers the ‘phz’ localised lowest unoccupied molecular orbital (LUMO) energy potentially favouring population of the 3MLCT(phz) state. This effect is more pronounced for [Re(CO)3Cl(dppp3)] with a more positive reduction potential (E½ = −1.16 vs Fc+/Fc in CH2Cl2) compared to [Re(CO)3Cl(dppp2)] (E½ = −1.20 V vs Fc+/Fc in CH2Cl2). For [Re(CO)3Cl(dppp2Br)], lowering of the LUMO energy results in an even more positive potential (E½ = −1.10 vs Fc+/Fc in CH2Cl2) and this can be seen to affect the photophysics. We find the excited state lifetime for each complex increases with decreasing dielectric constant, where their lifetime in toluene is greater than 100 times longer than that observed in d6-DMSO.
- Published
- 2019
19. Solid state structure and properties of phenyl diketopyrrolopyrrole derivatives
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William Lewis, Flavia Pop, E. Stephen Davies, Joshua Humphreys, Stephen P. Argent, Paul A. Hume, David B. Amabilino, and Alanna S. Murphy
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Steric effects ,Materials science ,Aryl ,Supramolecular chemistry ,Stacking ,Substituent ,02 engineering and technology ,Crystal structure ,General Chemistry ,Chromophore ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Crystallography ,chemistry.chemical_compound ,chemistry ,General Materials Science ,0210 nano-technology ,Single crystal - Abstract
The solid state supramolecular interactions of diketopyrrolopyrrole derivatives (DPPs) and their correlation with thin film optical properties are of particular interest because of the applications of these materials in organic electronics. In this study, we report the single crystal X-ray structures of several phenyl DPP derivatives, containing 4-methoxyphenyl, 4-hydroxyphenyl and 4-((tetrahydro-2H-pyran-2-yl)oxy)phenyl aryl units, and show how subtle changes in the substituent chains at side or end positions of the chromophore can lead to very different packing. They are compared to their phenyl counterpart to explore how the nature of both the alkyl chain and the aryl unit influence the optical properties that have been measured in solid and solution states. Importantly, for the three families of N-substituted compounds studied, the structures are changed by the conformation of the molecules and are apparently dominated by crystal packing effects where edge-to-face interactions are favoured rather than π stacking, with only one of the compounds showing a flat form, promoted by intermolecular contacts between the aromatic regions. It is therefore possible that the twist between DPP and phenyl units in crystals of DPPs results from edge-to-face interactions (rather than steric interactions between the N-substituent and the protons attached to the aromatic ring) that might be overcome in more extended structures. Hydrogen bonding dominates the packing to generate chains of DPP units for phenol derivatives. Remote bulky groups do affect the core conformation. The emission of the materials as thin films is dominated by local effects in the packing of the materials that are unique for each case as the structures are distinct from one another. Charge mobility (as calculated from the crystal structures) is not favoured because of twisted conformations and large displacement, but the sometimes high emission and large Stokes shift could make the materials interesting for other purposes, such as light emitters.
- Published
- 2021
20. Morpholino-Substituted BODIPY Species: Synthesis, Structure and Electrochemical Studies
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Neil R. Champness, William Lewis, Hawazen Hassanain, Deborah L. Kays, and E. Stephen Davies
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General Chemical Engineering ,010402 general chemistry ,Photochemistry ,01 natural sciences ,polymorphism ,Inorganic Chemistry ,Absorbance ,chemistry.chemical_compound ,Bathochromic shift ,hirshfeld surface analysis ,lcsh:QD901-999 ,Molecule ,General Materials Science ,Halogen bond ,010405 organic chemistry ,spectroelectrochemistry ,Chromophore ,Condensed Matter Physics ,Fluorescence ,0104 chemical sciences ,chemistry ,halogen bonding ,Halogen ,lcsh:Crystallography ,BODIPY ,boron-dipyrromethene dye - Abstract
Functionalization of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) chromophores at the 2,6-positions with iodo substituents and morpholino-substituted &alpha, methyl groups affords molecules with strong absorbance in the visible spectrum. The effect of such substitution on the solid-state arrangements, absorption, fluorescence and electronic properties of these dye molecules is reported. The spectroscopic and spectroelectrochemical measurements display intense absorptions in the UV-visible spectrum with bathochromic shifts, in comparison to unfunctionalized BODIPY, and a positive shift in redox potentials due to functionalisation of the BODIPY core. Halogen bonds are observed in the solid-state structures of both halogenated BODIPY species, which in one case leads to the formation of an unusual halogen bonded framework.
- Published
- 2020
21. Modulation of the optical properties of soluble N-alkylated 4-pyridyl diketopyrrolopyrrole derivatives
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Stephen P. Argent, E. Stephen Davies, Joshua Humphreys, Paul A. Hume, Ferdinando Malagreca, David B. Amabilino, and William Lewis
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Crystallography ,Absorption spectroscopy ,Hydrogen bond ,Chemistry ,Absorption band ,Process Chemistry and Technology ,General Chemical Engineering ,Alkoxy group ,Protonation ,Crystal structure ,Absorption (chemistry) ,Lone pair - Abstract
The absorption and fluorescence properties of N-alkylated 3,6-di (pyridin-4-yl)-2,5-dihydropyrrolo [3,4-c]pyrrole-1,4-dione (PyrDPP NH) derivatives in solution and the solid state are reported, along with the modulation of these properties under varying acidity or basicity. The compounds with hexyl (PyrDPP N-Hex) and methoxy ethoxy ethyl (PyrDPP N-MEE) chains were synthesised from PyrDPP NH giving highly soluble dyes. In addition, the mono-substituted derivatives were also isolated. A range of solvents was explored to provide understanding regarding their potential use in applications ranging from organic electronics to sensors. Optically the dyes are highly fluorescent and, as a result of N-alkylation breaking the hydrogen bond network, emissive in the solid state with large Stokes shifts. The nature of the chain dictates the π interactions and packing of the materials, resulting in modulation of the solid-state absorption spectra and theoretical mobility predicted from the crystal structures. The methoxy ethoxy ethyl chain twists out of the plane and bends to allow considerable molecular overlap and small interchromophore displacement with strikingly similar π interactions to the parent PyrDPP NH, resulting in a contribution of H-type aggregation to the absorption band and an order of magnitude improvement in theoretical mobility compared with the hexyl analogue. In contrast, PyrDPP N-Hex possesses a distorted CH-π interaction between pyridyl and lactam units, with greater molecular displacement manifesting in dominant J -aggregation contribution to absorption band and moderate mobility. The results emphasise the potential for sidechain modification and show structural evidence for the potential benefits of the flexible polar chains. The nitrogen lone pair of the pyridyl ring can be protonated in acidic environment to produce a photometric response suggesting potential as a proton sensor. The mono-substituted compounds are responsive to both base and acid, making them interesting for molecular logic applications.
- Published
- 2022
22. Thionated Perylene Diimide–Phenothiazine Dyad: Synthesis, Structure, and Electrochemical Studies
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E. Stephen Davies, Nicholas Pearce, Neil R. Champness, and William Lewis
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Organic electronics ,Steric effects ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Combinatorial chemistry ,Article ,0104 chemical sciences ,lcsh:Chemistry ,chemistry.chemical_compound ,lcsh:QD1-999 ,chemistry ,Diimide ,Phenothiazine ,Molecule ,Moiety ,0210 nano-technology ,Imide ,Perylene - Abstract
Perylene diimides (PDIs) are promising candidates for n-type semiconductor materials and, thus, for use in organic electronics. Thionation of the imide moiety provides an efficient strategy to control the donor–acceptor gap of these types of compounds, although the degree and selectivity of thionation can be hard to achieve. Through the design of a sterically encumbered PDI–phenothiazine dyad, a previously unattained geminal thionation pattern has been realized, providing the first example of a perylene-monoimide-monothioimide. The electrochemical and solid-state structural properties of this uniquely thionated dyad are reported and compared to those of the nonthionated parent molecule. It is found that thionation enhances the electron affinity of the PDI core, affecting electrochemical and spectroelectochemcial behavior of the dyad without significantly affecting the solid-state packing of the molecules.
- Published
- 2018
23. Self-Assembly of Chiral-at-End Diketopyrrolopyrroles: Symmetry Dependent Solution and Film Optical Activity and Photovoltaic Performance
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Flavia Pop, David B. Amabilino, James P. Monks, E. Stephen Davies, Roderick C. I. MacKenzie, Paul A. Hume, MOLTECH-Anjou, and Université d'Angers (UA)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Circular dichroism ,Spin coating ,Absorption spectroscopy ,Organic solar cell ,[CHIM.ORGA]Chemical Sciences/Organic chemistry ,Chemistry ,Organic Chemistry ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Catalysis ,Polymer solar cell ,0104 chemical sciences ,Crystallography ,[CHIM]Chemical Sciences ,Molecule ,Self-assembly ,Thin film ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
Chiral thiophene-diketopyrrolopyrrole derivatives have been synthesised to investigate the potential of stereochemistry and symmetry as a means of modulating properties by influencing self-assembly of these purely organic materials. In particular, derivatives of diketopyrrolopyrrole were employed because of their proven interest as dyes, especially for organic solar cells. The natural product myrtenal was used as the source of stereochemistry, introduced through a Krohnke reaction of a thiophene-bearing pyridinium salt and diketopyrrolopyrroles were prepared through Suzuki coupling with this chiral moiety at one end only as well as at both ends. Absorption spectroscopy and electrochemistry confirmed the potential suitability of the compounds for photovoltaic devices. The nanostructures formed by the compounds have been probed with circular dichroism spectroscopy in solution and in films. It is shown that a chiral C2 symmetric molecule assembles in solution giving a strong circular dichroic signal while as a film this optical activity is nulled, whereas an asymmetric homologue is most optically active as a thin film. The X-ray crystal structure of the asymmetric compound shows a polar order of the molecules that might explain this observation. The lack of optical activity in solution is very likely a result of the high solubility of the compound. The results reaffirm the sensitivity of circular dichroism spectroscopy to inter-chromophore organisation, whereas absorption spectroscopy in the visible region reveals only slight changes to the bands. The differing order in the compounds also affects their performance in bulk heterojunction photovoltaic devices. Atomic force microscopy of the blended thin films with the fullerene derivative usually employed (PC61 BM) showed that smooth and well mixed films were achieved, with the conditions required during spin coating depending greatly on the derivative, because of their differing solubility. The apparently better performance of the symmetrical compound (although with very low efficiency) is probably a result of the alignment of the molecules inferred by the circular dichroism experiments, whereas the asymmetric compound presumably adopts a twisted supramolecular organisation.
- Published
- 2018
24. Heterobimetallic [NiFe] Complexes Containing Mixed CO/CN– Ligands: Analogs of the Active Site of the [NiFe] Hydrogenases
- Author
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E. Stephen Davies, Jeremiah P. Tidey, Charlene L. Sodipo, Alexander J. Blake, Graham J. Jones, Carlo U. Perotto, Jonathan McMaster, William Lewis, and Martin Schröder
- Subjects
biology ,Hydride ,Chemistry ,Active site ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Crystallography ,law ,biology.protein ,Molecule ,Density functional theory ,Singlet state ,Physical and Theoretical Chemistry ,0210 nano-technology ,Electron paramagnetic resonance ,Bimetallic strip - Abstract
The development of synthetic analogs of the active sites of [NiFe] hydrogenases remains challenging, and, in spite of the number of complexes featuring a [NiFe] center, those featuring CO and CN- ligands at the Fe center are under-represented. We report herein the synthesis of three bimetallic [NiFe] complexes [Ni(N2S2)Fe(CO)2(CN)2], [Ni(S4)Fe(CO)2(CN)2], and [Ni(N2S3)Fe(CO)2(CN)2] that each contain a Ni center that bridges through two thiolato S donors to a {Fe(CO)2(CN)2} unit. X-ray crystallographic studies on [Ni(N2S3)Fe(CO)2(CN)2], supported by DFT calculations, are consistent with a solid-state structure containing distinct molecules in the singlet (S = 0) and triplet (S = 1) states. Each cluster exhibits irreversible reduction processes between -1.45 and -1.67 V vs Fc+/Fc and [Ni(N2S3)Fe(CO)2(CN)2] possesses a reversible oxidation process at 0.17 V vs Fc+/Fc. Spectroelectrochemical infrared (IR) and electron paramagnetic resonance (EPR) studies, supported by density functional theory (DFT) calculations, are consistent with a NiIIIFeII formulation for [Ni(N2S3)Fe(CO)2(CN)2]+. The singly occupied molecular orbital (SOMO) in [Ni(N2S3)Fe(CO)2(CN)2]+ is based on Ni 3dz2 and 3p S with the S contributions deriving principally from the apical S-donor. The nature of the SOMO corresponds to that proposed for the Ni-C state of the [NiFe] hydrogenases for which a NiIIIFeII formulation has also been proposed. A comparison of the experimental structures, and the electrochemical and spectroscopic properties of [Ni(N2S3)Fe(CO)2(CN)2] and its [Ni(N2S3)] precursor, together with calculations on the oxidized [Ni(N2S3)Fe(CO)2(CN)2]+ and [Ni(N2S3)]+ forms suggests that the binding of the {Fe(CO)(CN)2} unit to the {Ni(CysS)4} center at the active site of the [NiFe] hydrogenases suppresses thiolate-based oxidative chemistry involving the bridging thiolate S donors. This is in addition to the role of the Fe center in modulating the redox potential and geometry and supporting a bridging hydride species between the Ni and Fe centers in the Ni-C state.
- Published
- 2018
25. Core-Substituted Naphthalene Diimides: Influence of Substituent Conformation on Strong Visible Absorption
- Author
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Constance R. Pfeiffer, William Lewis, E. Stephen Davies, Neil R. Champness, Samuel Quinn, and Jonathan McMaster
- Subjects
Tertiary amine ,010405 organic chemistry ,Substituent ,General Chemistry ,Chromophore ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Absorbance ,chemistry.chemical_compound ,Naphthalene diimides, Dyes, Electrochemistry, UV/Vis Spectroscopy, X-ray Diffraction ,chemistry ,Morpholine ,Absorption (chemistry) ,Naphthalene ,Visible spectrum - Abstract
Functionalization of the aromatic core of naphthalene diimide (NDI) chromophores with morpholine substituents leads to molecules with strong absorbance in the visible spectrum. The shift of absorption maxima to lower energy is determined not only by the degree of substitution but also by the relative conformation and orientation of the tertiary amine with respect to the plane of the NDI.
- Published
- 2017
26. Synthesis and characterisation of rylene diimide dimers using molecular handcuffs
- Author
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E. Stephen Davies, Philipp Langer, Nicholas A. Besley, Katherine Wickham, Matteo Baldoni, Lixu Yang, Elena Besley, and Neil R. Champness
- Subjects
010405 organic chemistry ,Chemistry ,Dimer ,Intermolecular force ,General Chemistry ,010402 general chemistry ,Excimer ,01 natural sciences ,3. Good health ,0104 chemical sciences ,Ion ,Crystallography ,chemistry.chemical_compound ,Diimide ,Molecule ,Absorption (chemistry) ,Perylene - Abstract
A strategy for positioning, and loosely connecting, molecules in close proximity using mechanically interlocked handcuffs is described. The strategy is demonstrated using rylene diimides, creating dimeric structures in which two components are linked through pillar[5]arene/imidazolium rotaxanes. Investigation of the resulting molecules demonstrates intriguing and new properties that arise from placing these redox active dye molecules together, allowing interactions, whilst allowing the molecules to separate as required. In particular we observe excimer emission from a perylene diimide dimer handcuff and the formation of an unusual radical anion π-dimer upon double reduction of the same molecule. The latter exhibits a unique visible absorption profile for a PDI-based molecule. We demonstrate the flexibility of our approach by making an unprecedented mixed perylene diimide/naphthalene diimide dimer which also reveals interactions between the two components. Our synthetic strategy facilitates the creation of unusual dimeric structures and allows the investigation of intermolecular interactions and the effects they have on electronic and magnetic properties.
- Published
- 2019
27. Electrochemical and spectroelectrochemical investigations of perylene peri-tetracarbonyl species
- Author
-
Neil R. Champness, E. Stephen Davies, and Nicholas Pearce
- Subjects
chemistry.chemical_classification ,Process Chemistry and Technology ,General Chemical Engineering ,Chromophore ,Electron acceptor ,Photochemistry ,Electrochemistry ,Redox ,chemistry.chemical_compound ,chemistry ,Electronic effect ,Oxidation process ,Imide ,Perylene - Abstract
The electronic effects of varying the nature of the carbonyl groups in a series of perylene-3,4,9,10-tetracarbonyl compounds have been investigated. The four carbonyl groups comprise of esters, imides and anhydrides and combinations thereof. The series has been extensively characterised by electrochemical methods and it is found that the combination of imide and anhydride groups enhances the electron accepting properties of the perylene core. In contrast, the perylene core is the most electron rich when each of the four peri-positions is functionalised with an ester group. In the case of tetra-esterified perylene a reversible oxidation process can also be observed. The nature of the carbonyl species provides a degree of redox potential tunability whilst maintaining similar optical properties of the chromophores. This suggests that careful selection of peri-substituents is important in the fabrication of optoelectronic devices incorporating 3,4,9,10-tetracarbonyl perylene species.
- Published
- 2020
28. Design and characterisation of bodipy sensitizers for dye-sensitized NiO solar cells
- Author
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Karel Zidek, Tõnu Pullerits, E. Stephen Davies, Gareth H. Summers, Christopher J. Wood, Elizabeth A. Gibson, Fiona Black, and Jean-François Lefebvre
- Subjects
Photocurrent ,Non-blocking I/O ,General Physics and Astronomy ,02 engineering and technology ,Chromophore ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,Triphenylamine ,01 natural sciences ,Acceptor ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Solar cell ,Thiophene ,Physical and Theoretical Chemistry ,BODIPY ,0210 nano-technology - Abstract
A series of photosensitizers for NiO-based dye-sensitized solar cells is presented. Three model compounds containing a triphenylamine donor appended to a boron dipyrromethene (bodipy) chromophore have been successfully prepared and characterised using emission spectroscopy, electrochemistry and spectroelectrochemistry, to ultimately direct the design of dyes with more complex structures. Carboxylic acid anchoring groups and thiophene spacers were appended to the model compounds to provide five dyes which were adsorbed onto NiO and integrated into dye-sensitized solar cells. Solar cells incorporating the simple Bodipy-CO₂H dye were surprisingly promising relative to the more complex dye 4. Cell performances were improved with dyes which had increased electronic communication between the donor and acceptor, achieved by incorporating a less hindered bodipy moiety. Further increases in performances were obtained from dyes which contained a thiophene spacer. Thus, the best performance was obtained for 7 which generated a very promising photocurrent density of 5.87 mA cm(-2) and an IPCE of 53%. Spectroelectrochemistry combined with time-resolved transient absorption spectroscopy were used to determine the identity and lifetime of excited state species. Short-lived (ps) transients were recorded for 4, 5 and 7 which are consistent with previous studies. Despite a longer lived (25 ns) charge-separated state for 6/NiO, there was no increase in the photocurrent generated by the corresponding solar cell.
- Published
- 2016
29. Synthesis and Photophysical Study of a [NiFe] Hydrogenase Biomimetic Compound Covalently Linked to a Re-diimine Photosensitizer
- Author
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Michelle L. Hamilton, Joe Dawson, Michael W. George, James A. Calladine, E. Stephen Davies, Martin Schröder, Fabio Ghiotto, Jonathan McMaster, Michael Towrie, Peter A. Summers, and Xue-Z. Sun
- Subjects
Hydrogenase ,Spectrophotometry, Infrared ,Population ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Inorganic Chemistry ,Electron transfer ,Biomimetics ,Forum Article ,Electrochemistry ,Physical and Theoretical Chemistry ,Amines ,education ,Diimine ,education.field_of_study ,Quenching (fluorescence) ,Photosensitizing Agents ,010405 organic chemistry ,Chemistry ,0104 chemical sciences ,Rhenium ,Covalent bond ,Intramolecular force ,Excited state ,Spectrophotometry, Ultraviolet ,Oxidation-Reduction - Abstract
The synthesis, photophysics, and photochemistry of a linked dyad ([Re]-[NiFe2]) containing an analogue ([NiFe2]) of the active site of [NiFe] hydrogenase, covalently bound to a Re-diimine photosensitizer ([Re]), are described. Following excitation, the mechanisms of electron transfer involving the [Re] and [NiFe2] centers and the resulting decomposition were investigated. Excitation of the [Re] center results in the population of a diimine-based metal-to-ligand charge transfer excited state. Reductive quenching by NEt3 produces the radically reduced form of [Re], [Re]− (kq = 1.4 ± 0.1 × 107 M–1 s–1). Once formed, [Re]− reduces the [NiFe2] center to [NiFe2]−, and this reduction was followed using time-resolved infrared spectroscopy. The concentration dependence of the electron transfer rate constants suggests that both inter- and intramolecular electron transfer pathways are involved, and the rate constants for these processes have been estimated (kinter = 5.9 ± 0.7 × 108 M–1 s–1, kintra = 1.5 ± 0.1 × 105 s–1). For the analogous bimolecular system, only intermolecular electron transfer could be observed (kinter = 3.8 ± 0.5 × 109 M–1 s–1). Fourier transform infrared spectroscopic studies confirms that decomposition of the dyad occurs upon prolonged photolysis, and this appears to be a major factor for the low activity of the system toward H2 production in acidic conditions., Excitation of the [Re] center in the linked-dyad complex ([Re]-[NiFe2]) populates the 3MLCT excited state, and reductive quenching by NEt3 produces [Re]−. [Re]− reduces the [NiFe2] center to [NiFe2]− via inter- and intramolecular electron transfer pathways (kinter = 5.9 ± 0.7 × 108 M−1 s−1, kintra = 1.5 ± 0.1 × 105 s−1). For the analogous bimolecular system, where only intermolecular electron transfer could be observed, kinter = 3.8 ± 0.5 × 109 M−1 s−1.
- Published
- 2015
30. Crystal structure and magnetic properties of di-copper and di-zinc complexes with di-2-pyridyl ketone oxime
- Author
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E. Stephen Davies, Michael Remesic, Kiyoshi Chandler, Barry L. Westcott, Guy Crundwell, Jonathan McMaster, and Kevin M. Knopf
- Subjects
chemistry.chemical_classification ,Ketone ,010405 organic chemistry ,Ligand ,chemistry.chemical_element ,Zinc ,Crystal structure ,010402 general chemistry ,Oxime ,01 natural sciences ,Chloride ,Copper ,Medicinal chemistry ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,law ,Materials Chemistry ,medicine ,Organic chemistry ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,medicine.drug - Abstract
The heteroyclic ligand di-2-pyridyl ketone oxime (dpko) was reacted with MBr2·xH2O (M = Cu, Zn), affording several novel complexes. [Cu2(dpko)2Br4][CuBr4] and Zn(dpko)Br2 complexes are analogs of previously reported chloride complexes, and both are structurally and spectroscopically similar to the chloride analogs, [Cu2(dpko)2Cl4]Cl2 and Zn(dpko)Cl2; however, [Cu2(dpko)2Br4][CuBr4] crystallizes as the [CuBr4]2 − salt, while Zn(dpko)X2 exhibits a previously unreported disorder at the oxime site, which we now believe to also found to be present in the Zn(dpko)Cl2 analog. We also present EPR data for both [Cu2(dpko)2Br4][CuBr4] and [Cu2(dpko)2Cl4]Cl2.
- Published
- 2016
31. Heterobimetallic [NiFe] Complexes Containing Mixed CO/CN
- Author
-
Carlo U, Perotto, Charlene L, Sodipo, Graham J, Jones, Jeremiah P, Tidey, Alexander J, Blake, William, Lewis, E Stephen, Davies, Jonathan, McMaster, and Martin, Schröder
- Subjects
Models, Molecular ,Carbon Monoxide ,Cyanides ,Hydrogenase ,Molecular Structure ,Coordination Complexes ,Nickel ,Catalytic Domain ,Iron ,Quantum Theory ,Crystallography, X-Ray ,Ligands - Abstract
The development of synthetic analogs of the active sites of [NiFe] hydrogenases remains challenging, and, in spite of the number of complexes featuring a [NiFe] center, those featuring CO and CN
- Published
- 2018
32. Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene‐1,2‐dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units
- Author
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E. Stephen Davies, Muhammad Zubair, Carola Schulzke, James P. Dicks, C. David Garner, Jonathan McMaster, and Claire Wilson
- Subjects
chemistry.chemical_element ,Photochemistry ,Medicinal chemistry ,Redox ,Inorganic Chemistry ,chemistry.chemical_compound ,Delocalized electron ,chemistry ,Cyclopentadienyl complex ,Catalytic cycle ,Pyran ,Trifluoroacetic acid ,Cobalt ,Ene reaction - Abstract
The compounds [(η5-C5H5)Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized and characterized by elemental analysis, 1H NMR, mass spectrometry and X-ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH2Cl2 solution each compound undergoes a reversible one-electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5:1 excess of trifluoroacetic acid the one-electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [1]y, [2]y and [3]y (y = 0 or –1) and the monoprotonated forms [2H]z and [3H]z (z = +1 or 0), and this has provided insight into the nature of the redox-active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene-1,2-dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring-opened form of the molybdenum cofactor of oxygen-atom-transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle.
- Published
- 2015
33. From Cook to Chef: Facilitating the Transition from Recipe-driven to Open-ended Research-based Undergraduate Chemistry Lab Activities
- Author
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Anna Bertram, Michael W. George, Neil R. Thomas, M. Jonathan Fray, Kyle W. Galloway, Rossana R. Wright, E. Stephen Davies, Ross M. Denton, and Katharine L. Reid
- Subjects
Learning experience ,Engineering ,business.industry ,Research based ,Recipe ,Pedagogy ,Mathematics education ,Chemistry (relationship) ,Cognitive skill ,Plan (drawing) ,business - Abstract
This paper describes the development of mini-research projects in the third year practical chemistry course at the University of Nottingham for the MSci(Hons) Chemistry degree. The aim of these developments is to bridge the gap between ‘recipe-style’ experiments in the first and second year courses and research projects undertaken in the fourth year or in industry. There is much evidence that, having been given this opportunity to plan and design their own experiment, students exhibit higher-order cognitive skills, which can lead to a more valuable learning experience.
- Published
- 2014
34. Photochemical Dihydrogen Production Using an Analogue of the Active Site of [NiFe] Hydrogenase
- Author
-
Martin Schröder, Magnus W. D. Hanson-Heine, Khuong Q. Vuong, Nicholas A. Besley, Fabio Ghiotto, Jonathan McMaster, E. Stephen Davies, Peter A. Summers, Joe Dawson, Michael W. George, and Xue-Z. Sun
- Subjects
Quenching (fluorescence) ,Hydrogenase ,biology ,010405 organic chemistry ,Chemistry ,Active site ,Infrared spectroscopy ,Photochemical Processes ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,3. Good health ,Inorganic Chemistry ,chemistry.chemical_compound ,Electron transfer ,Spectroscopy, Fourier Transform Infrared ,Electrochemistry ,biology.protein ,Structural isomer ,Dimethylformamide ,Physical and Theoretical Chemistry ,Fourier transform infrared spectroscopy ,Hydrogen - Abstract
Photoproduction of dihydrogen (H2) by a low molecular weight analogue of the active site of [NiFe] hydrogenase has been investigated by reduction of the [NiFe2] cluster, 1, by a photosensitier PS (PS = [ReCl(CO)3(bpy)] or [Ru(bpy)3][PF6]2). Reductive quenching of the (3)MLCT excited state of the photosensitizer by NEt3 or N(CH2CH2OH)3 (TEOA) generates PS(•-), and subsequent intermolecular electron transfer to 1 produces the reduced anionic form of 1. Time-resolved infrared spectroscopy (TRIR) has been used to probe the intermediates throughout the reduction of 1 and subsequent photocatalytic H2 production from [HTEOA][BF4], which was monitored by gas chromatography. Two structural isomers of the reduced form of 1 (1a(•-) and 1b(•-)) were detected by Fourier transform infrared spectroscopy (FTIR) in both CH3CN and DMF (dimethylformamide), while only 1a(•-) was detected in CH2Cl2. Structures for these intermediates are proposed from the results of density functional theory calculations and FTIR spectroscopy. 1a(•-) is assigned to a similar structure to 1 with six terminal carbonyl ligands, while calculations suggest that in 1b(•-) two of the carbonyl groups bridge the Fe centers, consistent with the peak observed at 1714 cm(-1) in the FTIR spectrum for 1b(•-) in CH3CN, assigned to a ν(CO) stretching vibration. Formation of 1a(•-) and 1b(•-) and production of H2 was studied in CH3CN, DMF, and CH2Cl2. Although the more catalytically active species (1a(•-) or 1b(•-)) could not be determined, photocatalysis was observed only in CH3CN and DMF.
- Published
- 2014
35. Tuning the interactions between electron spins in fullerene-based triad systems
- Author
-
Bradley E. Thomas, E. Stephen Davies, Andrei N. Khlobystov, Maria A. Lebedeva, Thomas W. Chamberlain, and Martin Schröder
- Subjects
Fullerene ,fullerene triads ,fullerene dimers ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Full Research Paper ,law.invention ,lcsh:QD241-441 ,lcsh:Organic chemistry ,law ,medicine ,Physics::Atomic and Molecular Clusters ,Molecule ,Triplet state ,Electron paramagnetic resonance ,lcsh:Science ,carbon nanomaterials ,Spins ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,Triad (anatomy) ,spin–spin interactions ,3. Good health ,0104 chemical sciences ,Crystallography ,medicine.anatomical_structure ,electrochemistry ,Intramolecular force ,lcsh:Q ,EPR ,Ground state - Abstract
A series of six fullerene–linker–fullerene triads have been prepared by the stepwise addition of the fullerene cages to bridging moieties thus allowing the systematic variation of fullerene cage (C60 or C70) and linker (oxalate, acetate or terephthalate) and enabling precise control over the inter-fullerene separation. The fullerene triads exhibit good solubility in common organic solvents, have linear geometries and are diastereomerically pure. Cyclic voltammetric measurements demonstrate the excellent electron accepting capacity of all triads, with up to 6 electrons taken up per molecule in the potential range between −2.3 and 0.2 V (vs Fc+/Fc). No significant electronic interactions between fullerene cages are observed in the ground state indicating that the individual properties of each C60 or C70 cage are retained within the triads. The electron–electron interactions in the electrochemically generated dianions of these triads, with one electron per fullerene cage were studied by EPR spectroscopy. The nature of electron–electron coupling observed at 77 K can be described as an equilibrium between doublet and triplet state biradicals which depends on the inter-fullerene spacing. The shorter oxalate-bridged triads exhibit stronger spin–spin coupling with triplet character, while in the longer terephthalate-bridged triads the intramolecular spin–spin coupling is significantly reduced.
- Published
- 2014
36. Modification of coordination networks through a photoinduced charge transfer process
- Author
-
Timothy L. Easun, Michael W. George, Xue-Zhong Sun, Neil R. Champness, E. Stephen Davies, Thomas J. Reade, Alexander J. Blake, and Junhua Jia
- Subjects
Crystal ,Bridging (networking) ,Stereochemistry ,Chemistry ,Coordination network ,Infrared spectroscopy ,General Chemistry ,Photochemistry - Abstract
A metal-bearing coordination network synthesised from Re(2,2′-bipyridine-5,5′-dicarboxylate)(CO)3Cl bridging ligands and Cu(II) nodes, [{Cu(DMF)(H2O)[LRe(CO)3Cl]}·DMF]∞ReCu, undergoes an irreversible photoinduced charge transfer process. We demonstrate using time-resolved IR spectroscopy the nature of this photoinduced process and how, under suitable conditions, it is possible to initiate irreversible modification of the crystal through induction of the charge transfer process. As a result we are able to use the photoinduced process, which arises purely as a result of the structure of the coordination network, to write on crystals.
- Published
- 2014
37. Electron transfer dynamics and excited state branching in a charge-transfer platinum(<scp>ii</scp>) donor–bridge-acceptor assembly
- Author
-
Oleg V. Bouganov, E. Stephen Davies, Gregory M. Greetham, Sergei A. Tikhomirov, Anthony J. H. M. Meijer, Igor V. Sazanovich, Paul A. Scattergood, Michael Towrie, Julia A. Weinstein, Alexander S. Stasheuski, Anthony W. Parker, and Milan Delor
- Subjects
Inorganic Chemistry ,chemistry.chemical_classification ,Electron transfer ,chemistry.chemical_compound ,Chemistry ,Singlet oxygen ,Excited state ,Ultrafast laser spectroscopy ,Electron acceptor ,Photochemistry ,Ground state ,Triple bond ,Acceptor - Abstract
A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ∼50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ∼1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 μs and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state.
- Published
- 2014
38. Photoinduced charge separation in a PtII acetylide donor–acceptor triad based on 2-(1-pyrazole)-pyridine modified with naphthalene mono-imide electron acceptor
- Author
-
E. Stephen Davies, Julia A. Weinstein, Michael Towrie, Igor V. Sazanovich, Anthony J. H. M. Meijer, Mohammed A. H. Alamiry, and Robert D. Bennett
- Subjects
chemistry.chemical_classification ,Chemistry ,General Chemical Engineering ,Acetylide ,General Chemistry ,Electron acceptor ,Photochemistry ,Acceptor ,Photoinduced electron transfer ,chemistry.chemical_compound ,Electron transfer ,Photoinduced charge separation ,Excited state ,Triplet state - Abstract
A class of molecular electron transfer cascades—those based on PtII complexes of 2-(1-pyrazole)-pyridine (pzpy) ligands—are reported. The synthesis of a new electron-acceptor imide-modified pzpy ligands is reported, and their application to transition-metal chemistry demonstrated by the synthesis of the PtII chloride and acetylide complexes. These donor–acceptor assemblies are promising models for investigation of photoinduced charge separation. Accordingly, picosecond time-resolved infrared (TRIR) and femtosecond transient absorption (TA) studies have been undertaken to elucidate the nature and dynamics of the lowest excited states in Pt(NAP-pyr-pyrazole)(–CC–Ph–C7H15)2. It has been established that the initial population of an MLL'CT excited state in the chromophoric [Pt(pyridine-pyrazole)(acetylide)] core is followed by an electron transfer to the naphthalimide (NAP) acceptor, forming a charge-separated state. This state is characterized by a large shift in ν(CO) vibrations of the NAP acceptor, as well as by a very intense and broad [×10 times in comparison to ν(CO)] asymmetric acetylide stretch which incorporates –CC–Pt–CC– framework and occurs at approximately 300 cm–1 lower in energy than its ground-state counterpart. In CH2Cl2 at room temperature, the charge-separated state with the lifetime of 150 ps collapses into an almost isoenergetic NAP-localized triplet state; the rate of this transformation changes upon decreasing the temperature to 263 K. This final excited state, 3NAP-(pyr-pyrazole)Pt(–CC–Ph–C7H15)2, has an unusually long, for PtII complexes, excited-state lifetime of tens of microseconds. The work demonstrates the possibility of tuning excited-state properties in this new class of PtII chromophores designed for electron-transfer cascades.
- Published
- 2013
39. Bis-thioether-Substituted Perylene Diimides: Structural, Electrochemical, and Spectroelectrochemical Properties
- Author
-
William Lewis, E. Stephen Davies, Anna G. Slater, Alexander J. Blake, Jonathan McMaster, Neil R. Champness, and Stephen P. Argent
- Subjects
Models, Molecular ,chemistry.chemical_classification ,Molecular Structure ,Spectrophotometry, Infrared ,Organic Chemistry ,Electron Spin Resonance Spectroscopy ,Electrochemical Techniques ,Crystal structure ,Sulfides ,Crystallography, X-Ray ,Imides ,Electrochemistry ,Photochemistry ,law.invention ,chemistry.chemical_compound ,Delocalized electron ,Thioether ,chemistry ,Diimide ,law ,Spectrophotometry, Ultraviolet ,Electron paramagnetic resonance ,Perylene ,Alkyl - Abstract
The synthesis and separation of the 1,6- and 1,7- isomers of N,N'-bis(alkyl)diadamantylthio-3,4,9,10-perylenetetracarboxylic acid diimide are reported. Investigations of the structural, electrochemical, spectroscopic, and spectroelectrochemical properties of the isomers reveal a sequence of electrochemically and chemically reversible reduction processes for both isomers. Three X-ray crystal structures are reported including a pair of 1,6- and 1,7-isomers demonstrating the twist of the perylene core in the solid state. Our studies thoroughly characterize the mono- and direduced states of the two isomers allowing unequivocal characterization of the reduced species by UV-vis and IR spectroscopic measurements. EPR studies also allow direct identification of the monoreduced PTCDI species and spectroscopic measurements confirm the delocalization of electronic density around the carbonyl moieties of the reduced species.
- Published
- 2013
40. Stabilising the lowest energy charge-separated state in a {metal chromophore – fullerene} assembly: a tuneable panchromatic absorbing donor–acceptor triad
- Author
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Julia A. Weinstein, Milan Delor, Igor V. Sazanovich, Martin Schröder, E. Stephen Davies, Andrei N. Khlobystov, Thomas W. Chamberlain, Mikhail Suyetin, Maria A. Lebedeva, Elena Besley, and Paul A. Scattergood
- Subjects
Fullerene ,010405 organic chemistry ,Chemistry ,Solvatochromism ,Infrared spectroscopy ,General Chemistry ,Chromophore ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Absorption band ,Excited state ,Ultrafast laser spectroscopy ,Triplet state - Abstract
Photoreduction of fullerene and the consequent stabilisation of a charge-separated state in a donor-acceptor assembly have been achieved, overcoming the common problem of a fullerene-based triplet state being an energy sink that prevents charge-separation. A route to incorporate a C60-fullerene electron acceptor moiety into a catecholate-Pt(ii)-diimine photoactive dyad, which contains an unusually strong electron donor, 3,5-di-tert-butylcatecholate, has been developed. The synthetic methodology is based on the formation of the aldehyde functionalised bipyridine-Pt(ii)-3,5-di-tert-butylcatechol dyad which is then added to the fullerene cage via a Prato cycloaddition reaction. The resultant product is the first example of a fullerene-diimine-Pt-catecholate donor-acceptor triad, C60bpy-Pt-cat. The triad exhibits an intense solvatochromic absorption band in the visible region due to catechol-to-diimine charge-transfer, which, together with fullerene-based transitions, provides efficient and tuneable light harvesting of the majority of the UV/visible spectral range. Cyclic voltammetry, EPR and UV/vis/IR spectroelectrochemistry reveal redox behaviour with a wealth of reversible reduction and oxidation processes forming multiply charged species and storing multiple redox equivalents. Ultrafast transient absorption and time resolved infrared spectroscopy, supported by molecular modelling, reveal the formation of a charge-separated state [C60 -bpy-Pt-cat+] with a lifetime of ∼890 ps. The formation of cat+ in the excited state is evidenced directly by characteristic absorption bands in the 400-500 nm region, while the formation of C60 - was confirmed directly by time-resolved infrared spectroscopy, TRIR. An IR-spectroelectrochemical study of the mono-reduced building block (C60-bpy)PtCl2, revealed a characteristic C60 - vibrational feature at 1530 cm-1, which was also detected in the TRIR spectra. This combination of experiments offers the first direct IR-identification of C60 - species in solution, and paves the way towards the application of transient infrared spectroscopy to the study of light-induced charge-separation in C60-containing assemblies, as well as fullerene films and fullerene/polymer blends in various OPV devices. Identification of the unique vibrational signature of a C60-anion provides a new way to follow photoinduced processes in fullerene-containing assemblies by means of time-resolved vibrational spectroscopy, as demonstrated for the fullerene-transition metal chromophore assembly with the lowest energy charge-separated excited state.
- Published
- 2016
41. Direct Measurement of Electron Transfer in Nanoscale Host-Guest Systems: Metallocenes in Carbon Nanotubes
- Author
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Thomas W. Chamberlain, Robert L. McSweeney, Maria A. Lebedeva, Elena Besley, E. Stephen Davies, Andrei N. Khlobystov, and Matteo Baldoni
- Subjects
Nanotube ,Organic Chemistry ,Fermi level ,Ab initio ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Carbon nanotube ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,0104 chemical sciences ,law.invention ,Coulometry ,chemistry.chemical_compound ,symbols.namesake ,Electron transfer ,chemistry ,Chemical physics ,law ,Cobaltocene ,symbols ,Cyclic voltammetry ,0210 nano-technology - Abstract
Electron-transfer processes play a significant role in host-guest interactions and determine physicochemical phenomena emerging at the nanoscale that can be harnessed in electronic or optical devices, as well as biochemical and catalytic systems. A novel method for qualifying and quantifying the electronic doping of single walled carbon nanotubes (SWNTs) using electrochemistry has been developed that establishes a direct link between these experimental measurements and ab initio DFT calculations. Metallocenes such as cobaltocene and methylated ferrocene derivatives were encapsulated inside SWNTs (1.4 nm diameter) and cyclic voltammetry (CV) was performed on the resultant host-guest systems. The electron transfer between the guest molecules and the host SWNTs is measured as a function of shift in the redox potential (E1/2 ) of Co(II) /Co(I) , Co(III) /Co(II) and Fe(III) /Fe(II) . Furthermore, the shift in E1/2 is inversely proportional to the nanotube diameter. To quantify the amount of electron transfer from the guest molecules to the SWNTs, a novel method using coulometry was developed, allowing the mapping of the density of states and the Fermi level of the SWNTs. Correlated with theoretical calculations, coulometry provides an accurate indication of n/p-doping of the SWNTs.
- Published
- 2016
42. Synthesis of a Uranium(VI)-Carbene: Reductive Formation of Uranyl(V)-Methanides, Oxidative Preparation of a [R2C═U═O]2+ Analogue of the [O═U═O]2+ Uranyl Ion (R = Ph2PNSiMe3), and Comparison of the Nature of UIV═C, UV═C, and UVI═C Double Bonds
- Author
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Floriana Tuna, Oliver Cooper, Eric J. L. McInnes, Stephen T. Liddle, William Lewis, Fabrizio Moro, Jonathan McMaster, David P. Mills, E. Stephen Davies, and Alexander J. Blake
- Subjects
chemistry.chemical_classification ,Double bond ,chemistry.chemical_element ,General Chemistry ,Uranium ,Uranyl ,Biochemistry ,Medicinal chemistry ,Catalysis ,Ion ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Deprotonation ,chemistry ,Carbene ,Nuclear chemistry - Abstract
We report attempts to prepare uranyl(VI)- and uranium(VI) carbenes utilizing deprotonation and oxidation strategies. Treatment of the uranyl(VI)-methanide complex [(BIPMH)UO2Cl(THF)] [1, BIPMH = HC(PPh2NSiMe3)2] with benzyl-sodium did not afford a uranyl(VI)-carbene via deprotonation. Instead, one-electron reduction and isolation of di- and trinuclear [UO2(BIPMH)(μ-Cl)UO(μ-O){BIPMH}] (2) and [UO(μ-O)(BIPMH)(μ3-Cl){UO(μ-O)(BIPMH)}2] (3), respectively, with concomitant elimination of dibenzyl, was observed. Complexes 2 and 3 represent the first examples of organometallic uranyl(V), and 3 is notable for exhibiting rare cation–cation interactions between uranyl(VI) and uranyl(V) groups. In contrast, two-electron oxidation of the uranium(IV)-carbene [(BIPM)UCl3Li(THF)2] (4) by 4-morpholine N-oxide afforded the first uranium(VI)-carbene [(BIPM)UOCl2] (6). Complex 6 exhibits a trans-CUO linkage that represents a [R2C═U═O]2+ analogue of the uranyl ion. Notably, treatment of 4 with other oxidants such as Me3NO, C5...
- Published
- 2012
43. Thionated perylene diimides with intense absorbance in the near-IR
- Author
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Ben A. Llewellyn, E. Stephen Davies, Constance R. Pfeiffer, William Lewis, Neil R. Champness, and Mick Cooper
- Subjects
010405 organic chemistry ,Infrared ,Near-infrared spectroscopy ,Metals and Alloys ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Absorbance ,chemistry.chemical_compound ,chemistry ,Diimide ,Materials Chemistry ,Ceramics and Composites ,Amine gas treating ,Absorption (electromagnetic radiation) ,Perylene - Abstract
A synthetic strategy involving a combination of tetra-thionation and amine substitution in the bay region of a perylene diimide (PDI) leads to remarkable examples of neutral PDIs with intense absorption maxima in the near infrared. Generation of the corresponding monoanions red shifts the absorption profile to give short-wavelength infrared bands.
- Published
- 2015
44. A Perylene Diimide Rotaxane: Synthesis, Structure and Electrochemically Driven De-Threading
- Author
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Stephen P. Argent, Neil R. Champness, Harriott Nowell, Alexander J. Blake, Benjamin J. Slater, E. Stephen Davies, and William Lewis
- Subjects
chemistry.chemical_compound ,Rotaxane ,Chemistry ,Diimide ,Organic Chemistry ,General Chemistry ,Threading (protein sequence) ,Electrochemistry ,Photochemistry ,Redox ,Catalysis ,Perylene - Abstract
The first example of a [2]-rotaxane in which a perylene diimide acts as a recognition site has been synthesised and characterised. The interlocked nature of the compound has been verified by both NMR studies and an X-ray structure determination. Electrochemical investigations confirm that the nature of the redox processes associated with the perylene diimide are modified by the complexation process and that it is possible to mono-reduce the [2]-rotaxane to give a radical anion based rotaxane. Further reduction of the compound leads to de-threading of the macrocycle from the reduced PTCDI recognition site. Our synthetic strategies confirm the potential of PTCDI-based rotaxanes as viable targets for the preparation of complex interlocked species.
- Published
- 2011
45. Uranium-Carbon Multiple Bonding: Facile Access to the Pentavalent Uranium Carbene [U{C(PPh2NSiMe3)2}(Cl)2(I)] and Comparison of UVC and UIVC Bonds
- Author
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Oliver Cooper, William Lewis, Alexander J. Blake, E. Stephen Davies, Stephen T. Liddle, Jonathan McMaster, David P. Mills, Fabrizio Moro, Cooper, O, Mills, D, Mcmaster, J, Moro, F, Davies, E, Lewis, W, Blake, A, and Liddle, S
- Subjects
F-block element ,Metallo-Wittig reactivity ,Carbene ligand ,Chemistry (all) ,Inorganic chemistry ,chemistry.chemical_element ,General Medicine ,General Chemistry ,Uranium ,Uranium complexe ,Multiple bonds ,Catalysis ,Catalysi ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Multiple bonding ,Carbon ,Carbene - Abstract
(Chemical Equation Presented) A straightforward oxidation strategy affords the first pentavalent uranium carbene complex, 2. Owing to the structural similarity of 1 and 2, it was possible for the first time to directly probe the differences in U=C bonding on oxidation of UIVto UV. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA
- Published
- 2011
46. Building Multistate Redox-Active Architectures Using Metal-Complex Functionalized Perylene Bis-imides
- Author
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E. Stephen Davies, Alexander J. Blake, Gudrun Goretzki, Neil R. Champness, Stephen P. Argent, and John E. Warren
- Subjects
Chemistry ,Stereochemistry ,Redox ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,Crystallography ,Ferrocene ,visual_art ,visual_art.visual_art_medium ,Redox active ,Physical and Theoretical Chemistry ,Single crystal ,Perylene - Abstract
A series of multistate redox-active architectures has been synthesized, structurally characterized, and their optical and redox properties investigated. Specifically, two redox-active ferrocene or cobalt-dithiolene moieties have been introduced to the "bay" region of perylene-bisimides. Three of these disubstituted perylene-bisimide species have been structurally characterized by single crystal X-ray diffraction, confirming the twisted nature of the central perylene core. The first isomeric pair of disubstituted perylene-bisimide isomers, N,N'-di-(n-butyl)-1,7-diferrocenyl-perylene-3,4:9,10-tetracarboxylic acid bisimide (2) and N,N'-di-(n-butyl)-1,6-diferrocenyl-perylene-3,4:9,10-tetracarboxylic acid bisimide (3), structurally characterized by single crystal X-ray diffraction are reported and compared. Structural characterization of the cobalt-dithiolene substituted perylene-bisimide, N,N'-di-(n-butyl)-1,7-dicyclopentadienyl-cobalt(II)-dithiolenyl-perylene-3,4:9,10-tetracarboxylic acid bisimide (4), reveals the expected twisting of the perylene core and confirms the ene-dithiolate geometry of the cobalt dithiolene moiety. Cyclic voltammetry measurements, coupled with spectroelectrochemcial and electron paramagnetic resonance studies, of 1-4, where 1 is N,N'-di-(n-butyl)-1,7-diethynylferrocenyl-perylene-3,4:9,10-tetracarboxylic acid bisimide, reveal the two anticipated perylene-bisimide based reductions. In addition, for the ferrocene substituted compounds, 1-3, a single reversible two-electron oxidation is seen with only a small degree of communication between the ferrocene groups observed in the 1,6-isomer where the two ferrocene groups are attached to the same naphthyl moiety. In the case of 4, two reversible reductions associated with the cobalt-dithiolene moieties are observed, confirming communication across the reduced perylene core.
- Published
- 2009
47. Unusual formation of a [NiSFe2(CO)6] cluster: a structural model for the inactive form of [NiFe] hydrogenase
- Author
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Alexander J. Blake, Jonathan McMaster, Qiang Wang, E. Stephen Davies, Claire Wilson, Martin Schröder, and Alessandro Perra
- Subjects
chemistry.chemical_classification ,Hydrogenase ,Spectrophotometry, Infrared ,Sulfide ,Iron ,Electron Spin Resonance Spectroscopy ,chemistry.chemical_element ,Crystallography, X-Ray ,Electrochemistry ,law.invention ,Inorganic Chemistry ,Bond length ,Crystallography ,chemistry.chemical_compound ,Nickel ,chemistry ,Thioether ,law ,Organometallic Compounds ,Electron paramagnetic resonance ,Group 2 organometallic chemistry - Abstract
The synthesis and characterisation of the trinuclear Ni-Fe complex [Ni(L(2))SFe(2)(CO)(6)] (1) formed from the reaction of [Ni(L(1))] with Fe(3)(CO)(12) is described. The single-crystal X-ray structure of 1 shows Ni(ii) bound to three thioether R(2)-S donors and bridged by a sulfide (S(2-)) group to two Fe(CO)(3) units. undergoes a reversible one-electron reduction process at E(1/2) = -1.62 V vs. Fc(+)/Fc to generate 1 (-), which has been characterised by UV-vis and IR spectroelectrochemistry and by EPR spectroscopy. DFT calculations on 1and 1 (-) reveal electronic structures that are delocalised across the NiFe(2) core. The SOMO in 1 (-) possesses Ni-Fe and Fe-Fe anti-bonding character and lies approximately in the plane defined by the equilateral triangle of Ni and Fe atoms. It possesses d-orbital contributions of 18.5, 15.0 and 19.8% for the Ni(1), Fe(1) and Fe(2) atoms, respectively. The Ni-S(sulfide) bond length in 1 [2.1654(7) A] is identical to that for the bridging sulfide found in the oxidised inactive form of the [NiFe] hydrogenase from D. vulgaris (2.16 A). Thus, 1 provides a useful comparison for biological [NiFe] centres bridged by sulfide donors.
- Published
- 2009
48. Bis-morpholine-Substituted Perylene Bisimides: Impact of Isomeric Arrangement on Electrochemical and Spectroelectrochemical Properties
- Author
-
E. Stephen Davies, Alexander J. Blake, John E. Warren, Stephen P. Argent, Gudrun Goretzki, Wassim Z. Alsindi, Jonathan McMaster, and Neil R. Champness
- Subjects
medicine.diagnostic_test ,Organic Chemistry ,Electrochemistry ,Chemical synthesis ,Redox ,chemistry.chemical_compound ,chemistry ,Morpholine ,Spectrophotometry ,Polymer chemistry ,medicine ,Organic chemistry ,Amine gas treating ,Imide ,Perylene - Abstract
The synthesis and separation of the 1,6- and 1,7- isomers of N,N'-bis(n-butyl)dimorpholino-3,4:9,10-perylenetetracarboxylic acid bisimide are reported. Investigations of the electrochemical and spectroscopic, in particular, spectroelectrochemical, properties of the two isomers reveal a sequence of electrochemically and chemically reversible redox processes for both isomers. Importantly, the 1,7-isomer of N,N'-bis(n-butyl)dimorpholino-3,4:9,10-perylenetetracarboxylic acid bisimide was observed to undergo a two-electron oxidation process, which contrasts with the behavior of both the corresponding 1,6-isomer and other related amino-substituted perylene bis-imide species.
- Published
- 2008
49. Probing the Solvent Dependent Photophysics of fac-[Re(CO)3(dppz-X2)Cl] (dppz-X2 = 11,12-X2-dipyrido[3,2-a:2′,3′-c]phenazine); X = CH3, H, F, Cl, CF3)
- Author
-
Marina K. Kuimova, Pavel Matousek, Michael W. George, E. Stephen Davies, Jonathan McMaster, Anthony W. Parker, Michael Towrie, Xue-Zhong Sun, Claire Wilson, Alexander J. Blake, Daniele J. Lampus, and Wassim Z. Alsindi
- Subjects
Light switch ,Stereochemistry ,Ligand ,Phenazine ,Resonance Raman spectroscopy ,Substituent ,Inorganic Chemistry ,Solvent ,chemistry.chemical_compound ,Crystallography ,chemistry ,Excited state ,Physical and Theoretical Chemistry ,HOMO/LUMO - Abstract
The results of electrochemical measurements, density-functional theory calculations, emission and time-resolved IR (TRIR) spectroscopic studies for fac-[ReCl(CO)3(dppz-X2)], (dppz = dipyrido[3,2-a:2',3'-c]phenazine; X = CH3, H, F, Cl, CF3) are reported. For all complexes the calculations show that the lowest unoccupied molecular orbital (LUMO) is a phenazine based orbital localized on the dppz ligand. We observe that three different excited states, IL pi pi*, metal-to-ligand charge-transfer (MLCT) (phen), and MLCT (phz), are formed depending upon the substituent on the dppz ligand and on the nature of the solvent. This means that both the energy and the nature of the photophysically active state(s) can be tuned by both chemical modification of dppz ligand and solvent properties. The excited-state dynamics in these systems is directly related to the mechanism of the "light switch effect", and ps-TRIR has allowed a deeper insight into this mechanism by being able to directly monitor the change in the population of the higher lying emissive phen-type (3)MLCT and IL pi pi* states and the dark (3)MLCT (phz) state depending on the different environmental factors.
- Published
- 2008
50. Controlled Assembly of Silver(I)-Pyridylfullerene Networks
- Author
-
E. Stephen Davies, Andrei N. Khlobystov, Jian Fan, Alexander J. Blake, Yu Wang, Martin Schröder, and Claire Wilson
- Subjects
Fullerene ,Silver ,Molecular Structure ,Chemistry ,Pyridines ,X-Rays ,Supramolecular chemistry ,Nanotechnology ,General Chemistry ,General Medicine ,Ligands ,Catalysis ,Models, Chemical ,Spectrophotometry ,Organometallic Compounds ,Self-assembly ,Fullerenes - Published
- 2007
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