ORCID Profile
0000-0002-1801-8132
Current Organisation
University of Oxford
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Informa UK Limited
Date: 19-08-2018
Publisher: Wiley
Date: 23-05-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2SC05923A
Abstract: Aromatic or antiaromatic ring currents – why not both? We use experimental NMR chemical shifts to identify both local and global ring currents in π-conjugated molecules.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4OB02507E
Abstract: We report the synthesis of four new cationic push–pull membrane probes based on a thiophene core and evaluate their photobiological properties.
Publisher: American Chemical Society (ACS)
Date: 24-07-2017
DOI: 10.1021/JACS.7B05386
Publisher: Wiley
Date: 17-09-2019
Publisher: American Chemical Society (ACS)
Date: 26-07-2016
Publisher: Wiley
Date: 11-07-2022
Abstract: A recent Research Article in this journal by Matito and co‐workers claimed that none of the oxidation states of a butadiyne‐linked six‐porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. Experimental data from NMR spectroscopy for a whole family of nanorings provide strong evidence for global ring currents. The NMR data reveal these ring currents directly, without needing analysis by density functional theory (DFT). Furthermore, DFT calculations reproduce the experimental results when a suitable functional is used.
Publisher: American Chemical Society (ACS)
Date: 04-03-2019
DOI: 10.26434/CHEMRXIV.7797533.V1
Abstract: Aromaticity can be a useful concept for predicting the behavior of excited states. Here we show that π-conjugated porphyrin nanorings exhibit size-dependent excited-state global aromaticity and antiaromaticity, for rings containing up to eight porphyrin subunits, although they have no significant global aromaticity in their neutral singlet ground states. Applying Baird’s law, odd rings ([4n] π-electrons) are aromatic in their excited states, whereas the excited states of even rings ([4n+2] π-electrons) are antiaromatic. These predictions are borne out by density functional theory (DFT) studies of the nucleus-independent chemical shift in the T1 triplet state of each ring, which reveal the critical importance of the triplet delocalization to the emergence of excited-state aromaticity. The singlet excited states (S1) are explored by measurements of the radiative rate and fluorescence peak wavelength, revealing a subtle odd-even alternation as a function of ring size, consistent with symmetry-breaking in antiaromatic excited states.
Publisher: American Chemical Society (ACS)
Date: 19-06-2015
DOI: 10.1021/JACS.5B04511
Publisher: American Chemical Society (ACS)
Date: 29-07-2019
DOI: 10.26434/CHEMRXIV.9120974
Abstract: Doping, through oxidation or reduction, is often used to modify the properties of π-conjugated oligomers. In most cases, the resulting charge distribution is difficult to determine. If the oligomer is cyclic and doping establishes global aromaticity or antiaromaticity, then it is certain that the charge is fully delocalized over the entire perimeter of the ring. Here we show that reduction of a six-porphyrin nanoring using decamethylcobaltocene results in global aromaticity (in the 6– state [90 π]) and antiaromaticity (in the 4– state [88 π]), consistent with Hückel’s rules. Aromaticity is assigned by NMR spectroscopy and density-functional theory calculations. br
Publisher: American Chemical Society (ACS)
Date: 04-03-2019
DOI: 10.26434/CHEMRXIV.7797533
Abstract: Aromaticity can be a useful concept for predicting the behavior of excited states. Here we show that π-conjugated porphyrin nanorings exhibit size-dependent excited-state global aromaticity and antiaromaticity, for rings containing up to eight porphyrin subunits, although they have no significant global aromaticity in their neutral singlet ground states. Applying Baird’s law, odd rings ([4n] π-electrons) are aromatic in their excited states, whereas the excited states of even rings ([4n+2] π-electrons) are antiaromatic. These predictions are borne out by density functional theory (DFT) studies of the nucleus-independent chemical shift in the T1 triplet state of each ring, which reveal the critical importance of the triplet delocalization to the emergence of excited-state aromaticity. The singlet excited states (S1) are explored by measurements of the radiative rate and fluorescence peak wavelength, revealing a subtle odd-even alternation as a function of ring size, consistent with symmetry-breaking in antiaromatic excited states.
Publisher: American Chemical Society (ACS)
Date: 19-07-2019
DOI: 10.26434/CHEMRXIV.8953565.V1
Abstract: Aromaticity is an important concept for predicting electronic delocalisation in molecules, particularly for designing organic semiconductors and single-molecule electronic devices. It is most simply defined by the ability of a cyclic molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that if a ring has [4n+2] π-electrons, it will be aromatic with an induced magnetisation that opposes the external field inside the ring, whereas if it has 4n π-electrons, it will be antiaromatic with the opposite magnetisation. This rule reliably predicts the behaviour of small molecules, typically with circuits of less than about 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit and whether Hückel’s rule is valid in much larger macrocycles. Here, we present evidence for global aromaticity in a wide variety of porphyrin nanorings, with circuits of up to 162 π-electrons (n = 40 diameter 5 nm). We show that aromaticity can be controlled by changing the molecular structure, oxidation state and three-dimensional conformation. Whenever a global ring current is observed, its direction is correctly predicted by Hückel’s rule. The magnitude of the current is maximised when the average oxidation state of the porphyrin units is around 0.5–0.7, when the system starts to resemble a conductor with a partially filled valence band. Our results show that aromaticity can arise in large macrocycles, bridging the size gap between ring currents in molecular and mesoscopic rings.
Publisher: Elsevier BV
Date: 09-2012
Publisher: American Chemical Society (ACS)
Date: 10-09-2019
DOI: 10.26434/CHEMRXIV.8953565.V2
Abstract: Aromaticity is an important concept for predicting electronic delocalisation in molecules, particularly for designing organic semiconductors and single-molecule electronic devices. It is most simply defined by the ability of a cyclic molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that if a ring has [4n+2] π-electrons, it will be aromatic with an induced magnetisation that opposes the external field inside the ring, whereas if it has 4n π-electrons, it will be antiaromatic with the opposite magnetisation. This rule reliably predicts the behaviour of small molecules, typically with circuits of less than about 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit and whether Hückel’s rule is valid in much larger macrocycles. Here, we present evidence for global aromaticity in a wide variety of porphyrin nanorings, with circuits of up to 162 π-electrons (n = 40 diameter 5 nm). We show that aromaticity can be controlled by changing the molecular structure, oxidation state and three-dimensional conformation. Whenever a global ring current is observed, its direction is correctly predicted by Hückel’s rule. The magnitude of the current is maximised when the average oxidation state of the porphyrin units is around 0.5–0.7, when the system starts to resemble a conductor with a partially filled valence band. Our results show that aromaticity can arise in large macrocycles, bridging the size gap between ring currents in molecular and mesoscopic rings.
Publisher: Springer Science and Business Media LLC
Date: 19-12-2016
DOI: 10.1038/NATURE20798
Abstract: Aromatic and antiaromatic molecules-which have delocalized circuits of [4n + 2] or [4n] electrons, respectively-exhibit ring currents around their perimeters. The direction of the ring current in an aromatic molecule is such as to generate a magnetic field that opposes the external field inside the ring (a 'diatropic' current), while the ring current in an antiaromatic molecule flows in the reverse direction ('paratropic'). Similar persistent currents occur in metal or semiconductor rings, when the phase coherence of the electronic wavefunction is preserved around the ring. Persistent currents in non-molecular rings switch direction as a function of the magnetic flux passing through the ring, so that they can be changed from diatropic ('aromatic') to paratropic ('antiaromatic') simply by changing the external magnetic field. As in molecular systems, the direction of the persistent current also depends on the number of electrons. The relationship between ring currents in molecular and non-molecular rings is poorly understood, partly because they are studied in different size regimes: the largest aromatic molecules have diameters of about one nanometre, whereas persistent currents are observed in microfabricated rings with diameters of 20-1,000 nanometres. Understanding the connection between aromaticity and quantum-coherence effects in mesoscopic rings provides a motivation for investigating ring currents in molecules of an intermediate size. Here we show, using nuclear magnetic resonance spectroscopy and density functional theory, that a six-porphyrin nanoring template complex, with a diameter of 2.4 nanometres, is antiaromatic in its 4+ oxidation state (80 π electrons) and aromatic in its 6+ oxidation state (78 π electrons). The antiaromatic state has a huge paramagnetic susceptibility, despite having no unpaired electrons. This work demonstrates that a global ring current can be promoted in a macrocycle by adjusting its oxidation state to suppress the local ring currents of its components.The discovery of ring currents around a molecule with a circumference of 7.5 nanometres, at room temperature, shows that quantum coherence can persist in surprisingly large molecular frameworks.
Publisher: American Chemical Society (ACS)
Date: 03-06-2014
DOI: 10.1021/JA504730J
Publisher: American Chemical Society (ACS)
Date: 05-04-2019
Publisher: American Chemical Society (ACS)
Date: 11-04-2018
DOI: 10.1021/JACS.8B02552
Abstract: We report the template-directed synthesis of a π-conjugated 14-porphyrin nanoball. This structure consists of two intersecting nanorings containing six and 10 porphyrin units. Fluorescence upconversion spectroscopy experiments demonstrate that electronic excitation delocalizes over the whole three-dimensional π system in less than 0.3 ps if the nanoball is bound to its templates or over 2 ps if the nanoball is empty.
Publisher: American Chemical Society (ACS)
Date: 15-10-2019
Publisher: American Chemical Society (ACS)
Date: 04-01-2018
DOI: 10.1021/JACS.7B10542
Abstract: We have employed the scanning tunneling microscope break-junction technique to investigate the single-molecule conductance of a family of 5,15-diaryl porphyrins bearing thioacetyl (SAc) or methylsulfide (SMe) binding groups at the ortho position of the phenyl rings (S2 compounds). These ortho substituents lead to two atropisomers, cis and trans, for each compound, which do not interconvert in solution under ambient conditions even at high temperatures, isomerization takes several hours (half-life 15 h at 140 °C for SAc in C
Publisher: Springer Science and Business Media LLC
Date: 20-01-2020
Publisher: Wiley
Date: 23-05-2016
Publisher: American Chemical Society (ACS)
Date: 17-05-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4SC02424A
Abstract: When light is absorbed by a nanoring consisting of 6–24 porphyrin units, the excitation delocalizes over the whole molecule within 200 fs. Highly symmetric nanorings exhibit thermally enhanced super-radiance.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CC02544G
Abstract: Supramolecular assemblies can show unusual splitting patterns in their NMR spectra, with the magnitude of the effect increasing with molecular size. A simple NMR relaxation experiment reveals the origin of the effect and provides information on tumbling rates and local electronic structure.
Publisher: Wiley
Date: 16-07-2013
Publisher: Springer Science and Business Media LLC
Date: 03-08-2022
DOI: 10.1038/S41467-022-31909-W
Abstract: Many spintronic devices rely on the presence of spin-polarized currents at zero magnetic field. This is often obtained by spin exchange-bias, where an element with long-range magnetic order creates magnetized states and displaces the hysteresis loop. Here we demonstrate that exchange-split spin states are observable and usable in the smallest conceivable unit: a single magnetic molecule. We use a redox-active porphyrin as a transport channel, coordinating a dysprosium-based single-molecule-magnet inside a graphene nano-gap. Single-molecule transport in magnetic field reveals the existence of exchange-split channels with different spin-polarizations that depend strongly on the field orientation, and comparison with the diamagnetic isostructural compound and milikelvin torque magnetometry unravels the role of the single-molecule anisotropy and the molecular orientation. These results open a path to using spin-exchange in molecular electronics, and offer a method to quantify the internal spin structure of single molecules in multiple oxidation states.
Publisher: American Chemical Society (ACS)
Date: 13-10-2020
DOI: 10.26434/CHEMRXIV.13073231.V1
Abstract: Polyyne polyrotaxanes, encapsulated cyclocarbon catenanes and other fascinating mechanically interlocked carbonrich architectures should become accessible if masked alkyne equivalents (MAEs) can be developed that are large enough to prevent unthreading of a macrocycle, and that can be cleanly unmasked under mild conditions. Here we report the synthesis of a new bulky MAE based on a t-butylbicyclo[4.3.1]decatriene. This MAE was used to synthesize a polyyne [2]rotaxane and a maskedpolyyne [3]rotaxane by Cadiot-Chodkiewicz coupling. Glaser cyclooligomerization of the [2]rotaxane gave masked cyclocarbon catenanes. The unmasking behavior of the catenanes and rotaxanes was tested by photolysis at a range of UV wavelengths. Photochemical unmasking did not proceed cleanly enough to prepare extended encapsulated polyyne polyrotaxanes. We highlight the scope and challenges involved with this approach to interlocked carbon-rich architectures.
Publisher: American Chemical Society (ACS)
Date: 28-02-2011
DOI: 10.1021/NN103588H
Abstract: We report on the noncovalent binding of conjugated porphyrin oligomers to small diameter single-walled carbon nanotubes (SWNTs) and highlight two remarkable observations. First, the binding of the oligomers to SWNTs is so strong that it induces mechanical strain on the nanotubes in solution. The magnitudes of the strains are comparable to those found in solid-state studies. Comparable strains are not observed in any other SWNT-supramolecular complexes. Second, large decreases in polymer band gap with increasing length of the oligomer lead to the formation of a type-II heterojunction between long chain oligomers and small-diameter nanotubes. This is demonstrated by the observation of enhanced red-shifts for the nanotube interband transitions. These complexes offer considerable promise for photovoltaic devices.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1TC05951C
Abstract: NIR OLEDs are achieved by blending ethyne-linked zinc(II) porphyrin pentamers into a red-emitting push–pull polymeric host matrix (PIDT-2TPD). We report external quantum efficiencies of 2.0 % with peak emission at 830 nm, confirming the promise of porphyrin oligomers for non-toxic NIR OLEDs.
Publisher: Springer Science and Business Media LLC
Date: 02-07-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP04444A
Abstract: Ladder formation and planarisation do not enhance delocalisation in the triplet excited states of linear porphyrin oligomers.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2017
DOI: 10.1038/NCOMMS14842
Abstract: The exchange interaction, J , between two spin centres is a convenient measure of through bond electronic communication. Here, we investigate quantum interference phenomena in a bis-copper six-porphyrin nanoring by electron paramagnetic resonance spectroscopy via measurement of the exchange coupling between the copper centres. Using an analytical expression accounting for both dipolar and exchange coupling to simulate the time traces obtained in a double electron electron resonance experiment, we demonstrate that J can be quantified to high precision even in the presence of significant through-space coupling. We show that the exchange coupling between two spin centres is increased by a factor of 4.5 in the ring structure with two parallel coupling paths as compared to an otherwise identical system with just one coupling path, which is a clear signature of constructive quantum interference.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP07424J
Abstract: Excitation wavelength-dependent EPR and ENDOR reveal localization of the triplet state in twisted conformations of porphyrin oligomers.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8SC00130H
Abstract: We demonstrate that a photochromic spironaphthoxazine switch operates with excellent fatigue resistance and high conversion when irradiated at 405/561 nm in a range of media including living cells.
Publisher: American Chemical Society (ACS)
Date: 29-07-2019
DOI: 10.26434/CHEMRXIV.9120974.V1
Abstract: Doping, through oxidation or reduction, is often used to modify the properties of π-conjugated oligomers. In most cases, the resulting charge distribution is difficult to determine. If the oligomer is cyclic and doping establishes global aromaticity or antiaromaticity, then it is certain that the charge is fully delocalized over the entire perimeter of the ring. Here we show that reduction of a six-porphyrin nanoring using decamethylcobaltocene results in global aromaticity (in the 6– state [90 π]) and antiaromaticity (in the 4– state [88 π]), consistent with Hückel’s rules. Aromaticity is assigned by NMR spectroscopy and density-functional theory calculations.
Publisher: Wiley
Date: 24-02-2011
Publisher: American Chemical Society (ACS)
Date: 07-07-2017
Publisher: Wiley
Date: 21-01-2021
Publisher: American Chemical Society (ACS)
Date: 06-03-2015
Publisher: American Chemical Society (ACS)
Date: 08-12-2014
DOI: 10.1021/JZ5022153
Abstract: The topology of a conjugated molecule plays a significant role in controlling both the electronic properties and the conformational manifold that the molecule may explore. Fully π-conjugated molecular nanorings are of particular interest, as their lowest electronic transition may be strongly suppressed as a result of symmetry constraints. In contrast, the simple Kasha model predicts an enhancement in the radiative rate for corresponding linear oligomers. Here we investigate such effects in linear and cyclic conjugated molecules containing between 6 and 42 butadiyne-linked porphyrin units (corresponding to 600 C-C bonds) as pure monodisperse oligomers. We demonstrate that as the diameter of the nanorings increases beyond ∼10 nm, its electronic properties tend toward those of a similarly sized linear molecule as a result of excitation localization on a subsegment of the ring. However, significant differences persist in the nature of the emitting dipole polarization even beyond this limit, arising from variations in molecular curvature and conformation.
Publisher: American Chemical Society (ACS)
Date: 16-12-2021
DOI: 10.26434/CHEMRXIV-2021-V8B0K
Abstract: The luminescence and electroluminescence of an ethyne-linked zinc(II) porphyrin pentamer have been investigated, by testing blends in two different conjugated polymer matrices, at a range of concentrations. The best results were obtained for blends with the conjugated polymer PIDT-2TPD, at a porphyrin loading of 1 wt%. This host matrix was selected because the excellent overlap between its emission spectrum and the absorption spectrum of the porphyrin oligomer leads to efficient energy transfer. Thin films of this blend exhibit intense fluorescence in the near-infrared (NIR), with a peak emission wavelength of 886 nm and a photoluminescent quantum yield (PLQY) of 27% in the solid state. Light-emitting diodes (LEDs) fabricated with this blend as the emissive layer achieve average external quantum efficiencies (EQE) of 2.0% with peak emission at 830 nm and a turn-on voltage of 1.6 V. This performance is remarkable for a singlet NIR-emitter 93% of the photons are emitted in the NIR (λ 700 nm), indicating that conjugated porphyrin oligomers are promising emitters for non-toxic NIR OLEDs.
Publisher: Wiley
Date: 11-07-2022
Abstract: A recent Research Article in this journal by Matito and co‐workers claimed that none of the oxidation states of a butadiyne‐linked six‐porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. Experimental data from NMR spectroscopy for a whole family of nanorings provide strong evidence for global ring currents. The NMR data reveal these ring currents directly, without needing analysis by density functional theory (DFT). Furthermore, DFT calculations reproduce the experimental results when a suitable functional is used.
Publisher: Springer Science and Business Media LLC
Date: 02-02-2014
DOI: 10.1038/NN.3646
Abstract: Recent evidence in vitro suggests that the tuft dendrites of pyramidal neurons are capable of evoking local NMDA receptor-dependent electrogenesis, so-called NMDA spikes. However, it has so far proved difficult to demonstrate their existence in vivo. Moreover, it is not clear whether NMDA spikes are relevant to the output of pyramidal neurons. We found that local NMDA spikes occurred in tuft dendrites of layer 2/3 pyramidal neurons both spontaneously and following sensory input, and had a large influence on the number of output action potentials. Using two-photon activation of an intracellular caged NMDA receptor antagonist (tc-MK801), we found that isolated NMDA spikes typically occurred in multiple branches simultaneously and that sensory stimulation substantially increased their probability. Our results demonstrate that NMDA receptors have a vital role in coupling the tuft region of the layer 2/3 pyramidal neuron to the cell body, enhancing the effectiveness of layer 1 input.
Publisher: American Chemical Society (ACS)
Date: 25-09-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9SC05717J
Abstract: Break down of the Born–Oppenheimer approximation is caused by mixing of electronic and vibrational transitions in the radical cations of some conjugated polymers, resulting in unusually intense vibrational bands known as infrared active vibrations (IRAVs).
Publisher: American Chemical Society (ACS)
Date: 10-09-2019
DOI: 10.26434/CHEMRXIV.8953565
Abstract: Aromaticity is an important concept for predicting electronic delocalisation in molecules, particularly for designing organic semiconductors and single-molecule electronic devices. It is most simply defined by the ability of a cyclic molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that if a ring has [4n+2] π-electrons, it will be aromatic with an induced magnetisation that opposes the external field inside the ring, whereas if it has 4n π-electrons, it will be antiaromatic with the opposite magnetisation. This rule reliably predicts the behaviour of small molecules, typically with circuits of less than about 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit and whether Hückel’s rule is valid in much larger macrocycles. Here, we present evidence for global aromaticity in a wide variety of porphyrin nanorings, with circuits of up to 162 π-electrons (n = 40 diameter 5 nm). We show that aromaticity can be controlled by changing the molecular structure, oxidation state and three-dimensional conformation. Whenever a global ring current is observed, its direction is correctly predicted by Hückel’s rule. The magnitude of the current is maximised when the average oxidation state of the porphyrin units is around 0.5–0.7, when the system starts to resemble a conductor with a partially filled valence band. Our results show that aromaticity can arise in large macrocycles, bridging the size gap between ring currents in molecular and mesoscopic rings. /
Publisher: Wiley
Date: 17-09-2019
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP01787A
Abstract: The unique combination of EPR, DFT and novel large-scale simulation methods provides information on exchange coupling between metal centers in molecular wires.
Publisher: American Chemical Society (ACS)
Date: 07-02-2018
Abstract: Extended triisopropylsilyl end-capped polyynes have been prepared from the corresponding tetracobalt complexes by removing the complexed dicobalt tetracarbonyldiphenylphosphinomethane (Co
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP06167A
Abstract: Temperature-dependent changes in the UV-vis-NIR absorption spectrum of a butadiyne linked porphyrin dimer have been used to determine the height of the energy barrier to torsional rotation.
Publisher: Wiley
Date: 21-01-2021
Publisher: American Chemical Society (ACS)
Date: 18-12-2014
DOI: 10.1021/JA510663Z
Publisher: American Chemical Society (ACS)
Date: 04-08-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP07348H
Abstract: We compare the absorption and magnetic circular dichroism (MCD) spectra of a series of porphyrin oligomers – dimer, tetramer, and hexamer – bound in a linear or cyclic fashion.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Harry Anderson.