Ben Powell

Exact exchange and the density functional theory of metal-to-ligand charge-transfer in fac-Ir(ppy)3

Publisher: Elsevier BV

Date: 06-2016

DOI: 10.1016/J.ORGEL.2016.02.039

Superconductivity suppression and peak resistivity enhancement for thin crystals of κ‐(BEDT‐TTF)₂Cu(SCN)₂

Publisher: Wiley

Date: 22-03-2012

DOI: 10.1002/PSSB.201100711

Guest-Induced Multistep to Single-Step Spin-Crossover Switching in a 2-D Hofmann-Like Framework with an Amide-Appended Ligand

Publisher: American Chemical Society (ACS)

Date: 21-07-2022

DOI: 10.1021/ACS.INORGCHEM.2C01253

Abstract: A detailed study of the two-dimensional (2-D) Hofmann-like framework [Fe(furpy)

Electronic correlations in organometallic complexes

Publisher: Elsevier BV

Date: 05-2011

DOI: 10.1016/J.CPLETT.2011.03.090

Preparation of metal mixed plastic superconductors: Electrical properties of tin-antimony thin films on plastic substrates

Publisher: AIP Publishing

Date: 05-2009

DOI: 10.1063/1.3123803

Abstract: Metal mixed polymers are a cheap and effective way to produce flexible metals and superconductors. As part of an on-going effort to learn how to tune the properties of these systems with ion implantation, we present a study of the electrical properties of these systems prior to metal mixing. We show that the electrical properties of tin-antimony thin films are remarkably robust to variations in the substrate morphology. We demonstrate that the optical absorbance of the films at a fixed wavelength provides a reliable and reproducible characterization of the relative film thickness. We find that as the film thickness is reduced, the superconducting transition in the unimplanted thin films is broadened, but the onset of the transition remains at ∼3.7 K, the transition temperature of bulk Sn. This is in marked contrast to the behavior of metal mixed films, which suggests that the metal mixing process has a significant effect on the physics of the superconducting state beyond that achieved by reducing the film thickness alone.

Sensitivity of the photophysical properties of organometallic complexes to small chemical changes

Publisher: AIP Publishing

Date: 28-09-2010

DOI: 10.1063/1.3480981

Abstract: We investigate an effective model Hamiltonian for organometallic complexes that are widely used in optoelectronic devices. The two most important parameters in the model are J, the effective exchange interaction between the π and π∗ orbitals of the ligands, and ε∗, the renormalized energy gap between the highest occupied orbitals on the metal and on the ligand. We find that the degree of metal-to-ligand charge transfer character of the lowest triplet state is strongly dependent on the ratio ε∗/J. ε∗ is purely a property of the complex and can be changed significantly by even small variations in the complex’s chemistry, such as replacing substituents on the ligands. We find that small changes in ε∗/J can cause large changes in the properties of the complex, including the lifetime of the triplet state and the probability of injected charges (electrons and holes) forming triplet excitations. These results give some insight into the observed large changes in the photophysical properties of organometallic complexes caused by small changes in the ligands.

Towards quantum chemistry on a quantum computer

Publisher: Springer Science and Business Media LLC

Date: 10-01-2010

DOI: 10.1038/NCHEM.483

Abstract: Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications.

Interplay of dipoles and spins in κ−(BEDT

Publisher: American Physical Society (APS)

Date: 13-03-2020

DOI: 10.1103/PHYSREVB.101.125110

Multi-Redox Responsive Behavior in a Mixed-Valence Semiconducting Framework Based on Bis-[1,2,5]-thiadiazolo-tetracyanoquinodimethane

Publisher: American Chemical Society (ACS)

Date: 13-07-2022

DOI: 10.1021/JACS.2C03794

Abstract: The two-dimensional (2-D) framework, [Cu(BTDAT)(MeOH)] {BTDAT = bis-[1,2,5]-thiadiazolo-tetracyanoquinodimethane}, possesses remarkable multi-step redox properties, with electrochemical studies revealing six quasi-stable redox states in the solid state. In situ electron paramagnetic resonance and visible-near infrared spectroelectrochemistry elucidated the mechanism for these multi-step redox processes, as well as the optical and electrochromic behavior of the BTDAT ligand and framework. In studying the structural, spectroscopic, and electronic properties of [Cu(BTDAT)(MeOH)], the as-synthesized framework was found to exist in a mixed-valence state with thermally-activated semiconducting behavior. In addition to pressed pellet conductivity measurements, single-crystal conductivity measurements using a pre-patterned polydimethylsiloxane layer on a silicon substrate provide important insights into the anisotropic conduction pathways. As an avenue to further understand the electronic state of [Cu(BTDAT)(MeOH)], computational band structure calculations predicted delocalized electronic transport in the framework. On the balance of probabilities, we propose that [Cu(BTDAT)(MeOH)] is a Mott insulator (i.e., electron correlations cause a metal-insulator transition). This implies that the conductivity is incoherent. However, we are unable to distinguish between activated transport due to Coulombically bound electron-hole pairs and a hopping mechanism. The combined electrochemical, electronic, and optical properties of [Cu(BTDAT)(MeOH)] shine a new light on the experimental and theoretical challenges for electroactive framework materials, which are implicated as the basis of advanced optoelectronic and electrochromic devices.

Mechanomagnetics in Elastic Crystals: Insights from [Cu(acac)₂]

Publisher: Wiley

Date: 20-09-2019

DOI: 10.1002/ANGE.201907889

A unified explanation of the Kadowaki–Woods ratio in strongly correlated metals

Publisher: Springer Science and Business Media LLC

Date: 19-04-2009

DOI: 10.1038/NPHYS1249

On the origin of electrical conductivity in the bio-electronic material melanin

Publisher: AIP Publishing

Date: 27-02-2012

DOI: 10.1063/1.3688491

Abstract: The skin pigment melanin is one of a few bio-macromolecules that display electrical and photo-conductivity in the solid-state. A model for melanin charge transport based on amorphous semiconductivity has been widely accepted for 40 years. In this letter, we show that a central pillar in support of this hypothesis, namely experimental agreement with a hydrated dielectric model, is an artefact related to measurement geometry and non-equilibrium behaviour. Our results cast significant doubt on the validity of the amorphous semiconductor model and are a reminder of the difficulties of electrical measurements on low conductivity, disordered organic materials.

Gapless spinons and a field-induced soliton gap in the hyperhoneycomb Cu oxalate framework compound [(

Publisher: American Physical Society (APS)

Date: 13-10-2023

DOI: 10.1103/PHYSREVB.108.134418

Emergence of quasi-one-dimensional physics in a nearly-isotropic three-dimensional molecular crystal:Ab initiomodeling of

Publisher: American Physical Society (APS)

Date: 26-03-2015

DOI: 10.1103/PHYSREVB.91.125140

Phase diagram of thespin−12triangul

Publisher: American Physical Society (APS)

Date: 09-06-2015

DOI: 10.1103/PHYSREVB.91.245119

In-plane superfluid density and microwave conductivity of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: Evidence for d-wave pairing and resilient quasiparticles

Publisher: American Physical Society (APS)

Date: 07-08-2013

DOI: 10.1103/PHYSREVB.88.064501

Spin-state smectics in spin crossover materials

Publisher: AIP Publishing

Date: 10-05-2021

DOI: 10.1063/5.0045763

Abstract: We show that a simple two-dimensional model of spin crossover materials gives rise to spin-state smectic phases where the pattern of high-spin (HS) and low-spin (LS) metal centers spontaneously breaks rotational symmetry and translational symmetry in one direction only. The spin-state smectics are distinct thermodynamic phases and give rise to plateaus in the fraction of HS metal centers. Smectic order leads to lines of Bragg peaks in the x-ray and neutron scattering structure factors. We identify two smectic phases and show that both are ordered in one direction, but disordered in the other, and hence that their residual entropy scales with the linear dimension of the system. This is intermediate to spin-state ices (ex les of “spin-state liquids”) where the residual entropy scales with the system volume, and antiferroelastic ordered phases (ex les of “spin-state crystals”) where the residual entropy is independent of the size of the system.

Haldane Phase in the Hubbard Model at 2/3-Filling for the Organic Molecular CompoundMo

Publisher: American Physical Society (APS)

Date: 31-12-2014

DOI: 10.1103/PHYSREVLETT.113.267204

Magnetic excitations of the Cu2+

Publisher: American Physical Society (APS)

Date: 30-03-2018

DOI: 10.1103/PHYSREVB.97.104426

Frustration, ring exchange, and the absence of long-range order inEtMe3

Publisher: American Physical Society (APS)

Date: 07-04-2020

DOI: 10.1103/PHYSREVMATERIALS.4.044403

Relativistic effects in a phosphorescent Ir(III) complex

Publisher: American Physical Society (APS)

Date: 21-01-2011

DOI: 10.1103/PHYSREVB.83.041105

Haldane insulator protected by reflection symmetry in the doped Hubbard model on the three-legged ladder

Publisher: American Physical Society (APS)

Date: 19-12-2016

DOI: 10.1103/PHYSREVB.94.214418

Breakdown of the universality of the Kadowaki-Woods Ratio in multi-band metals

Publisher: American Physical Society (APS)

Date: 19-11-2015

DOI: 10.1103/PHYSREVB.92.195138

Models of organometallic complexes for optoelectronic applications

Publisher: Royal Society of Chemistry (RSC)

Date: 2010

DOI: 10.1039/C0JM01786H

Mechanomagnetics in Elastic Crystals: Insights from [Cu(acac)

Publisher: Wiley

Date: 20-09-2019

DOI: 10.1002/ANIE.201907889

Abstract: We predict that the magnetic properties of [Cu(acac)

A Tunable Metal–Organic Resistance Thermometer

Publisher: Wiley

Date: 14-12-2010

DOI: 10.1002/CPHC.201000762

Low-energy effective theories of the two-thirds filled Hubbard model on the triangular necklace lattice

Publisher: American Physical Society (APS)

Date: 16-07-2014

DOI: 10.1103/PHYSREVB.90.035120

Spin-Crossover 2-D Hofmann Frameworks Incorporating an Amide-Functionalized Ligand: N-(pyridin-4-yl)benzamide

Publisher: MDPI AG

Date: 03-2021

DOI: 10.3390/CHEMISTRY3010026

Abstract: Two analogous 2-D Hofmann-type frameworks, which incorporate the novel ligand N-(pyridin-4-yl)benzamide (benpy) [FeII(benpy)2M(CN)4]·2H2O (M = Pd (Pd(benpy)) and Pt (Pt(benpy))) are reported. The benpy ligand was explored to facilitate spin-crossover (SCO) cooperativity via amide group hydrogen bonding. Structural analyses of the 2-D Hofmann frameworks revealed benpy-guest hydrogen bonding and benpy-benpy aromatic contacts. Both analogues exhibited single-step hysteretic spin-crossover (SCO) transitions, with the metal-cyanide linker (M = Pd or Pt) impacting the SCO spin-state transition temperature and hysteresis loop width (Pd(benpy): T½↓↑: 201, 218 K, ∆T: 17 K and Pt(benpy): T½↓↑: 206, 226 K, ∆T: 20 K). The parallel structural and SCO changes over the high-spin to low-spin transition were investigated using variable-temperature, single-crystal, and powder X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. These studies indicated that the ligand–guest interactions facilitated by the amide group acted to support the cooperative spin-state transitions displayed by these two Hofmann-type frameworks, providing further insight into cooperativity and structure–property relationships.

Competition between superconductivity and weak localization in metal-mixed ion-implanted polymers

Publisher: American Physical Society (APS)

Date: 29-04-2010

DOI: 10.1103/PHYSREVB.81.144520

Dynamical Reduction of the Dimensionality of Exchange Interactions and the “Spin-Liquid” Phase of κ

Publisher: American Physical Society (APS)

Date: 25-08-2017

DOI: 10.1103/PHYSREVLETT.119.087204

Role of semiconductivity and ion transport in the electrical conduction of melanin

Publisher: Proceedings of the National Academy of Sciences

Date: 21-05-2012

DOI: 10.1073/PNAS.1119948109

Abstract: Melanins are pigmentary macromolecules found throughout the biosphere that, in the 1970s, were discovered to conduct electricity and display bistable switching. Since then, it has been widely believed that melanins are naturally occurring amorphous organic semiconductors. Here, we report electrical conductivity, muon spin relaxation, and electron paramagnetic resonance measurements of melanin as the environmental humidity is varied. We show that hydration of melanin shifts the comproportionation equilibrium so as to dope electrons and protons into the system. This equilibrium defines the relative proportions of hydroxyquinone, semiquinone, and quinone species in the macromolecule. As such, the mechanism explains why melanin at neutral pH only conducts when “wet” and suggests that both carriers play a role in the conductivity. Understanding that melanin is an electronic-ionic hybrid conductor rather than an amorphous organic semiconductor opens exciting possibilities for bioelectronic applications such as ion-to-electron transduction given its biocompatibility.

Toward High-Temperature Light-Induced Spin-State Trapping in Spin-Crossover Materials: The Interplay of Collective and Molecular Effects

Publisher: American Chemical Society (ACS)

Date: 12-05-2022

DOI: 10.1021/JACS.2C03202

Abstract: Spin-crossover (SCO) materials display many fascinating behaviors including collective phase transitions and spin-state switching controlled by external stimuli, e.g., light and electrical currents. As single-molecule switches, they have been fêted for numerous practical applications, but these remain largely unrealized-partly because of the difficulty of switching these materials at high temperatures. We introduce a semiempirical microscopic model of SCO materials combining crystal field theory with elastic intermolecular interactions. For realistic parameters, this model reproduces the key experimental results including thermally induced phase transitions, light-induced spin-state trapping (LIESST), and reverse-LIESST. Notably, we reproduce and explain the experimentally observed relationship between the critical temperature of the thermal transition,

Tight-Binding Approach to Pyrazine-Mediated Superexchange in Copper–Pyrazine Antiferromagnets

Publisher: American Chemical Society (ACS)

Date: 26-07-2021

DOI: 10.1021/ACS.INORGCHEM.1C00532

Gaseous Adsorption in Melanins: Hydrophilic Biomacromolecules with High Electrical Conductivities

Publisher: American Chemical Society (ACS)

Date: 11-11-2009

DOI: 10.1021/LA901290F

Abstract: The melanins are an important class of multifunctional biomacromolecules that possess a number of intriguing physical and chemical properties including electrical and photoconductivity. Unusually for a conducting organic material, eumelanin is hydrophilic and its electrical properties are strongly dependent on its hydration state. We have therefore measured adsorption isotherms for two polar adsorbates, water and ethanol, in the pressed powder pellets of synthetic eumelanin typically used in electrical studies. We show that a simple kinetic monolayer Langmuir model describes the adsorption and find that there are strong adsorbate-eumelanin interactions in both cases. These isotherms allow the proper scaling of electrical conductivity data and in doing so make progress toward a better understanding of eumelanin electrical properties, which is a critical prerequisite to the design of new eumelanin-like bioelectronic materials.

Elucidating the Spatial Arrangement of Emitter Molecules in Organic Light-Emitting Diode Films

Publisher: Wiley

Date: 07-02-2017

DOI: 10.1002/ANIE.201610727

Abstract: The effect of varying the emitter concentration on the structural properties of an archetypal phosphorescent blend consisting of 4,4'-bis(N-carbazolyl)biphenyl and tris(2-phenylpyridyl)iridium(III) has been investigated using non-equilibrium molecular dynamics (MD) simulations that mimic the process of vacuum deposition. By comparison with reflectometry measurements, we show that the simulations provide an accurate model of the average density of such films. The emitter molecules were found not to be evenly distributed throughout film, but rather they can form networks that provide charge and/or energy migration pathways, even at emitter concentrations as low as ≈5 weight percent. At slightly higher concentrations, percolated networks form that span the entire system. While such networks would give improved charge transport, they could also lead to more non-radiative pathways for the emissive state and a resultant loss of efficiency.

Hydration-controlled X-band EPR spectroscopy: A tool for unravelling the complexities of the solid-state free radical in eumelanin

Publisher: American Chemical Society (ACS)

Date: 19-04-2013

DOI: 10.1021/JP401615E

Abstract: Melanin, the human skin pigment, is found everywhere in nature. Recently it has gained significant attention for its potential bioelectronic properties. However, there remain significant obstacles in realizing its electronic potential, in particular, the identity of the solid-state free radical in eumelanin, which has been implicated in charge transport. We have therefore undertaken a hydration-controlled continuous-wave electron paramagnetic resonance study on solid-state eumelanin. Herein we show that the EPR signal from solid-state eumelanin arises predominantly from a carbon-centered radical but with an additional semiquinone free radical component. Furthermore, the spin densities of both of these radicals can be manipulated using water and pH. In the case of the semiquinone radical, the comproportionation reaction governs the pH- and hydration-dependent behavior. In contrast, the mechanism underlying the carbon-centered radical's pH- and hydration-dependent behavior is not clear consequently, we have proposed a new destacking model in which the intermolecular structure of melanin is disordered due to π-π destacking, brought about by the addition of water or increased pH, which increases the proportion of semiquinone radicals via the comproportionation reaction.

Effects of fluorination on iridium(III) complex phosphorescence: Magnetic circular dichroism and relativistic time-dependent density functional theory

Publisher: American Chemical Society (ACS)

Date: 16-02-2012

DOI: 10.1021/IC201899Z

Abstract: We use a combination of low temperature, high field magnetic circular dichroism, absorption, and emission spectroscopy with relativistic time-dependent density functional calculations to reveal a subtle interplay between the effects of chemical substitution and spin-orbit coupling (SOC) in a family of iridium(III) complexes. Fluorination at the ortho and para positions of the phenyl group of fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) cause changes that are independent of whether the other position is fluorinated or protonated. This is demonstrated by a simple linear relationship found for a range of measured and calculated properties of these complexes. Further, we show that the phosphorescent radiative rate, k(r), is determined by the degree to which SOC is able to hybridize T(1) to S(3) and that k(r) is proportional to the inverse fourth power of the energy gap between these excitations. We show that fluorination in the para position leads to a much larger increase of the energy gap than fluorination at the ortho position. Theory is used to trace this back to the fact that fluorination at the para position increases the difference in electron density between the phenyl and triazolyl groups, which distorts the complex further from octahedral symmetry, and increases the energy separation between the highest occupied molecular orbital (HOMO) and the HOMO-1. This provides a new design criterion for phosphorescent iridium(III) complexes for organic optoelectronic applications. In contrast, the nonradiative rate is greatly enhanced by fluorination at the ortho position. This may be connected to a significant redistribution of spectral weight. We also show that the lowest energy excitation, 1A, has almost no oscillator strength therefore, the second lowest excitation, 2E, is the dominant emissive state at room temperature. Nevertheless the mirror image rule between absorption and emission is obeyed, as 2E is responsible for both absorption and emission at all but very low (<10 K) temperatures.

Spin–Orbit Coupling in Phosphorescent Iridium(III) Complexes

Publisher: Wiley

Date: 22-07-2011

DOI: 10.1002/CPHC.201100397

Abstract: We study the excited states of two iridium(III) complexes with potential applications in organic light-emitting diodes: fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)(3)] and fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) [Ir(ptz)(3)]. Herein we report calculations of the excited states of these complexes from time-dependent density functional theory (TDDFT) with the zeroth-order regular approximation (ZORA). We show that results from the one-component formulation of ZORA, with spin-orbit coupling included perturbatively, accurately reproduce both the results of the two-component calculations and previously published experimental absorption spectra of the complexes. We are able to trace the effects of both scalar relativistic correction and spin-orbit coupling on the low-energy excitations and radiative lifetimes of these complexes. In particular, we show that there is an indirect relativistic stabilisation of the metal-to-ligand charge transfer (MLCT) states. This is important because it means that indirect relativistic effects increase the degree to which SOC can hybridise singlet and triplet states and hence plays an important role in determining the optical properties of these complexes. We find that these two compounds are remarkably similar in these respects, despite Ir(ppy)(3) and Ir(ptz)(3) emitting green and blue light respectively. However, we predict that these two complexes will show marked differences in their magnetic circular dichroism (MCD) spectra.

Linkage - International - Grant ID: LX0455413

Start Date: 08-2004

End Date: 06-2008

Amount: $87,200.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP180101483

Start Date: 2018

End Date: 12-2021

Amount: $357,072.00

Funder: Australian Research Council

ARC Future Fellowships - Grant ID: FT130100161

Start Date: 2014

End Date: 12-2017

Amount: $803,814.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE170100144

Start Date: 05-2017

End Date: 11-2017

Amount: $480,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP230100139

Start Date: 12-2023

End Date: 12-2026

Amount: $410,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0878523

Start Date: 2008

End Date: 03-2014

Amount: $624,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP200100305

Start Date: 2020

End Date: 06-2023

Amount: $660,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0559215

Start Date: 2005

End Date: 12-2008

Amount: $345,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0882224

Start Date: 2008

End Date: 03-2010

Amount: $440,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE120100181

Start Date: 03-2012

End Date: 12-2015

Amount: $650,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0557532

Start Date: 06-2005

End Date: 12-2008

Amount: $405,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE110100060

Start Date: 2011

End Date: 03-2012

Amount: $150,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP1093224

Start Date: 2010

End Date: 12-2013

Amount: $363,500.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP160100060

Start Date: 03-2016

End Date: 12-2019

Amount: $347,582.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP130100757

Start Date: 2013

End Date: 05-2016

Amount: $270,000.00

Funder: Australian Research Council