Weak Electronic Coupling Research Articles

Electron‐Penetrating in Heterointerface Engineering for Oxygen Evolution Reaction in Seawater Splitting

AbstractThe interfacial electric field (IEF) between heterogeneous units plays an important role in the electronic modulation of active centers during oxygen evolution reaction (OER). However, the weak electronic coupling between spatially separated IEFs limits the deep activation of metal sites on the surface of the catalyst. Herein, a proof‐of‐concept strategy is provided that imbed MS2 (M = Ni3Fe) species with high spin Fe orbits into heterogeneous units to promote the electron penetrating between IEFs. By designing a Fe2O3@MS/MS2@MOy model catalyst, the electronic interaction between adjacent IEFs is effectively enhanced for the deep oxidation of bimetals on the surface, breaking the competing relationship between adsorbed evolution mechanism (AEM) and lattice oxygen mechanism (LOM) of catalysts during OER. As a result, the onset overpotential of the synthesized electrode is only 171 mV, and it maintains excellent stability for more than 2300 h at a current density of 10 mA cm−2 in 1 M KOH + 0.5 M NaCl electrolyte.

Electronic Coupling in Triferrocenylpnictogens.

From a fundamental perspective, studies of novel mixed-valent complexes containing ferrocenyl units are motivated by the prospect of improving and extending electron transfer models and theories. Here, the series of triferrocenylpnictogens Fc3E was extended to the heavier analogues (E = As, Sb, and Bi), and the influence of the bridging atom was investigated with Fc3P as a reference. Electrochemical studies elucidate the effect of electrostatic contribution on the large redox splitting (ΔE 1) exhibited by the compounds and solvent stabilization in the case of Fc3As. Structural characterization of the triferrocenylpnictogens combined with spectroelectrochemical studies indicates weak electronic couplings in the related cations [Fc3E]+, suggesting a through-space mechanism.

Missing-cell defects in QCA wires: The ground and excited electronic states perspectives

Quantum Cellular Automata (QCA) technology offers promising prospects for designing molecular electronic circuits that operate at high frequencies and with ultra-low power consumption. QCA wires serve as crucial conduits for digital data transmission between logic gates. A series of QCA cells arranged sequentially forms these wires, with data written or read using paired nanogap electrodes. In this study, employing a simplified full-basis quantum mechanical model, we investigate the impact of single and double missing cells on the response function and output voltage of wires implemented within the two-dot QCA architecture. The electronic coupling between the quantum dots within each QCA cell stands out as a critical structural parameter influencing both the nonlinearity of the response function and the level of output voltage. Ground state analyses of wires affected by missing-cell defects suggest that employing QCA cells with weak electronic coupling could potentially enhance fault tolerance. However, examination of excited states reveals that reducing electronic coupling may compromise the thermal robustness of such defective QCA wires.

Unveiling the Interlayer Interaction in a 1H/1T TaS2 van der Waals Heterostructure.

This study delves into the intriguing properties of the 1H/1T-TaS2 van der Waals heterostructure, focusing on the transparency of the 1H layer to the charge density wave of the underlying 1T layer. Despite the sizable interlayer separation and metallic nature of the 1H layer, positive bias voltages result in a pronounced superposition of the 1T charge density wave structure on the 1H layer. The conventional explanation relying on tunneling effects proves insufficient. Through a comprehensive investigation combining low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, non-contact atomic force microscopy, and first-principles calculations, we propose an alternative interpretation. The transparency effect arises from a weak yet substantial electronic coupling between the 1H and 1T layers, challenging prior understanding of the system. Our results highlight the critical role played by interlayer electronic interactions in van der Waals heterostructures to determine the final ground states of the systems.

Carrier transport and mesomorphic properties of deformable fluorinated perylene bisimide bearing disiloxane chains

We synthesized liquid crystalline difluorinated perylene bisimide derivatives bearing oligosiloxane moieties. At room temperature, these compounds exhibited columnar phases which were stabilized thermodynamically, compared to that of a non-fluorinated analog. The absorption bands in the thin films of the fluorinated compounds exhibited a slight bathochromic shift compared to that in the solution state, indicating a weak electronic coupling between the fluorinated perylene bisimide cores in the columnar phases. The electron mobilities in the columnar phases of the difluorinated compounds were determined to be on the order of 10−2 cm2V−1s−1 at room temperature by the time-of-flight measurements. The LUMO levels of the difluorinated compounds were lowered by 0.1 eV from that of non-fluorinated analog. Anion radicals of the fluorinated compounds were stable as that of the non-fluorinated analog while dianions of the fluorinated compounds were unstable unlike that of the non-fluorinated analog. The difluorinated compounds was soft waxy solid. In particular, the 1,7-difluorinated derivative is deformable to form various shapes at room temperature. A study on the surface morphology of the thin film indicated formation of microscopic grooves, which should enhance the softness of the compound.

J-aggregates and two-dimensional materials indirect-coupling with polariton-assisted resonance energy transfer

Researching resonance energy transfer (RET) from one quantum emitter to another in the strong coupling regime can provide a new route to empower ultrafast quantum manipulations and possess fascinating technological frontiers. However, most of the reports only discussed the weak electronic coupling limit and incoherent energy transfer. Here, we establish a universal theory to investigate RET between two emitters weakly/strongly coupled to a plasmonic mode and analyze the dynamics of RET by utilizing a full-quantum method. Combining with our theory, we investigate the RET rate of a multilayer system in which J-aggregates/monolayer WS2 acts as the donor/acceptor. The calculated results verify that RET rates in the strong coupling regime increase two orders of magnitude compared to the weak coupling regime. Moreover, the coherent energy exchange between two detuned emitters is realized in the strong coupling regime by the time-dependent population calculations. The double Rabi splitting appears in the photoluminescence (PL) spectrum with sufficient RET rates (103ns−1) and coupling strength (g=60 meV). Our work demonstrates a quantitative calculation of RET rates and PL spectrum for the plasmon-biexciton coupled systems, providing a promising way for precise photochemical control, integrated optical device design and quantum information processing.

Giant Rashba-splitting of one-dimensional metallic states in Bi dimer lines on InAs(100).

Bismuth produces different types of ordered superstructures on the InAs(100) surface, depending on the growth procedure and coverage. The (2 × 1) phase forms at completion of one Bi monolayer and consists of a uniformly oriented array of parallel lines of Bi dimers. Scanning tunneling and core level spectroscopies demonstrate its metallic character, in contrast with the semiconducting properties expected on the basis of the electron counting principle. The weak electronic coupling among neighboring lines gives rise to quasi one-dimensional Bi-derived bands with open contours at the Fermi level. Spin- and angle-resolved photoelectron spectroscopy reveals a giant Rashba splitting of these bands, in good agreement with ab initio electronic structure calculations. The very high density of the dimer lines, the metallic and quasi one-dimensional band dispersion and the Rashba-like spin texture make the Bi/InAs(100)-(2 × 1) phase an intriguing system, where novel transport regimes can be studied.

Linear and nonlinear optical absorption of 2D monolayer NbOCl2

The in-layer crystal structure of a two-dimensional material is stable, but the interaction force between the atomic layers is much weaker. Niobium oxide dichloride (NbOCl2) not only has high second-order nonlinear coefficients unique to common monolayer two-dimensional materials but also weak electronic coupling between layers. These characteristics make NbOCl2 very suitable as a quantum light source in quantum optical systems. This article mainly studies the linear and nonlinear optical absorption of two-dimensional monolayer NbOCl2. The characterization means include a surface distance projection map and three views, total density of states, photoelectron spectrum, charge density difference, transition dipole moment density, one-photon absorption spectrum, and two-photon absorption spectrum. There is a size effect on the total density of states, photoelectronic energy spectrum, and one-photon absorption spectrum, that is, as the size increases, the total density of states is red-shift, the photoelectronic energy spectrum is blue-shift, and the absorption spectrum has a significant red-shift. The charge density difference indicates that there is charge transfer around the Nb atom of NbOCl2. The transition dipole moment density changes periodically. The study of the two-photon absorption spectrum shows that it is dominated by a one-step transition. In summary, our work provides an in-depth understanding of its optical properties and is of great significance for the miniaturization of quantum light sources.

Does a Blatter Radical Retain Its Open-Shell Character When Incorporated into Gold–Molecule–Gold Junctions?

One of the key issues for the use of organic radicals in high-performance molecular electronic, spintronic and thermoelectric devices is the retention, at room temperature, of their open-shell character when they are in contact with the metal electrodes of a junction. By means of first-principles quantum transport calculations, we have investigated the stability and the electronic transport properties of single-molecule junctions incorporating a Blatter radical (BR) with thiomethyl linker groups. Our calculations suggest that the BR can unequivocally retain its open-shell nature even when bound to gold electrodes through undercoordinated gold adatoms. Such a state cannot be destroyed by the surrounding solvent molecules and the applied bias. The calculated low-bias conductance values of junctions with BR, an oxidized BR derivative, and a closed-shell stilbene molecule are in quantitative agreement with the available experimental measurements. The small conductance of the BR can be associated with the localization of its π-type singly occupied and singly unoccupied molecular orbitals (SOMO and SUMO), leading to an asymmetrically weak electronic coupling to the two gold electrodes, even though these two orbitals lie very close to the Fermi energy. Furthermore, the nonmonotonic modulation of the junction conductance controlled by a charge gate can be used in experiments to further verify the presence of the unpaired electron. This proof may be realized in practice with an electrostatic solid-state or an electrochemical gate. Our findings deepen the current understanding of the radical–metal interfacial properties and facilitate the design of future radical-based multifunctional molecular devices.

Metal-Induced Fast Vibrational Energy Relaxation: Quantum Nuclear Effects Captured in Diabatic Independent Electron Surface Hopping (IESH-D) Method.

In this paper, we propose a simple approach to include quantum nuclear effects in the weak electronic coupling regime within the independent electron surface hopping (IESH) method for simulating nonadiabatic dynamics near metal surfaces. Our method uses electronic states in a diabatic basis, and electronic transitions between metal and molecular states are included using Landau-Zener theory. We benchmark our novel approach using a two-state model system for which exact results (obtained from Fermi's golden rule) are available. We further investigate the effect of metallic electrons on the rate and the pathway of vibrational energy relaxation.

Antisymmetric Exchange in a Real Copper Triangular Complex

The antisymmetric exchange, also known as the Dzyaloshinskii-Moriya interaction (DMI), is an effective interaction that may be at play in isolated complexes (with transition metals or lanthanides, for instance), nanoparticles, and highly correlated materials with adequate symmetry properties. While many theoretical works have been devoted to the analysis of single-ion zero-field splitting and to a lesser extent to symmetric exchange, only a few ab initio studies deal with the DMI. Actually, it originates from a subtle interplay between weak electronic interactions and spin-orbit couplings. This article aims to highlight the origin of this interaction from theoretical grounds in a real tri-copper(II) complex, capitalizing on previous methodological studies on bi-copper(II) model complexes. By tackling this three-magnetic-center system, we will first show that the multispin model Hamiltonian is appropriate for trinuclear (and likely for higher nuclearity) complexes, then that the correct application of the permutation relationship is necessary to explain the outcomes of the ab initio calculations, and finally, that the model parameters extracted from a binuclear model transfer well to the trinuclear complex. For a more theory-oriented purpose, we will show that the use of a simplified structural model allows one to perform more demanding electronic structure calculations. On this simpler system, we will first check that the previous transferability is still valid, prior to performing more advanced calculations on the derived two-magnetic-center model system. To this end, we will explain in detail the physics of the DMI in the copper triangle of interest, before advocating further theory/experiment efforts.

Molecular heterostructure by fusing graphene nanoribbons of different lengths through a pentagon ring junction

Graphene nanoribbons (GNRs) have attracted great research interest because of their widely tunable and unique electronic properties. The required atomic precision of GNRs can be realized via on-surface synthesis method. In this work, through a surface assisted reaction we have longitudinally fused the pyrene-based graphene nanoribbons (pGNR) of different lengths by a pentagon ring junction, and built a molecular junction structure on Au (111). The electronic properties of the structure are studied by scanning tunneling spectroscopy (STS) combined with tight binding (TB) calculations. The pentagon ring junction shows a weak electronic coupling effect on graphene nanoribbons, which makes the electronic properties of the two different graphene nanoribbons connected by a pentagon ring junction analogous to type I semiconductor heterojunctions.

Vibronic resonance along effective modes mediates selective energy transfer in excitonically coupled aggregates.

We recently proposed effective normal modes for excitonically coupled aggregates that exactly transform the energy transfer Hamiltonian into a sum of one-dimensional Hamiltonians along the effective normal modes. Identifying physically meaningful vibrational motions that maximally promote vibronic mixing suggested an interesting possibility of leveraging vibrational-electronic resonance for mediating selective energy transfer. Here, we expand on the effective mode approach, elucidating its iterative nature for successively larger aggregates, and extend the idea of mediated energy transfer to larger aggregates. We show that energy transfer between electronically uncoupled but vibronically resonant donor-acceptor sites does not depend on the intermediate site energy or the number of intermediate sites. The intermediate sites simply mediate electronic coupling such that vibronic coupling along specific promoter modes leads to direct donor-acceptor energy transfer, bypassing any intermediate uphill energy transfer steps. We show that the interplay between the electronic Hamiltonian and the effective mode transformation partitions the linear vibronic coupling along specific promoter modes to dictate the selectivity of mediated energy transfer with a vital role of interference between vibronic couplings and multi-particle basis states. Our results suggest a general design principle for enhancing energy transfer through synergistic effects of vibronic resonance and weak mediated electronic coupling, where both effects individually do not promote efficient energy transfer. The effective mode approach proposed here paves a facile route toward four-wavemixing spectroscopy simulations of larger aggregates without severely approximating resonant vibronic coupling.

Molecular design strategy for realizing vectorial electron transfer in photoelectrodes

<h2>Summary</h2> Vectorial electron transfer is essential for developing ideal artificial photosystems. Conventional photosensitizers with only strong electronic coupling, as used in photovoltaics, cannot achieve vectorial electron transfer because of their rapid charge recombination. Herein, we present a design strategy for integrating strong (∼600 cm⁻¹) and relatively weak (310 cm⁻¹) electronic coupling in a single molecule to realize vectorial electron transfer in dye-sensitized solar cells. Four sensitizers with donor-acceptor-π-spacer and anchoring group configurations are developed, and the electronic coupling in these sensitizers is controlled by the π-spacers of varying steric hindrances. Transient-absorption spectroscopies reveal the occurrence of vectorial electron transfer in the designed sensitizer by suppressing charge recombination via weakened electronic coupling between the acceptor and π-spacer and the efficient charge injection via strong electronic coupling between the donor and acceptor. The optimization of electronic coupling in the sensitizers improves the photovoltaic performances, achieving a power-conversion efficiency of 10.8%.

Understanding Diffusional Charge Transport within a Pyrene-Based Hydrogen-Bonded Organic Framework.

Electrochemically active hydrogen-bonded organic frameworks (HOFs) offer opportunities to study charge transport in supramolecular systems where the rate of movement of charges is dependent on weak electronic coupling between individual components. Here, we used potential-step chronoamperometric measurements on electrochemically active, drop-cast HOF-102 films to estimate both redox-hopping-based apparent diffusion coefficients for charge transport and rate constants for linker-to-linker charge transfer (hole transfer) in the mesoporous two-dimensional (2D) plane created by interlinker hydrogen bonding. Also present are one-dimensional columns formed by stacking pyrene units. However, because the HOF-102 crystallites containing these columns are oriented parallel to an underlying electrode, dynamics of charge transport (hole-transport) along the column axis, in contrast to the plane, are not directly probed by the electrochemical measurements. Furthermore, we employed electrochemical impedance spectroscopy to measure the electrical conductivity of the as-deposited films biased at various potentials. We found that both the neutral/singly oxidized and the singly oxidized/doubly oxidized pyrene linker redox couples of HOF-102 can engender hopping-based film conductivity within the 2D plane of HOF-102. Consistent with the radical cation and radical dication nature of the singly and doubly oxidized linkers, respectively, HOF-102 films are electrochromic. The measured values of in-plane charge-diffusion coefficients (∼10-10 to 10-11 cm2 s-1) and electrical conductivity (∼10-6 to 10-8 S cm-1) compare favorably with those for related redox-conductive MOFs and suggest that the transport and conductivity parameters for HOF-102 are sufficiently large to support electrocatalysis by subsequently installed catalysts in films─specifically, films of micron or greater thickness, corresponding to the equivalent hundreds of monolayers of closely packed (i.e., face-to-face-packed) pyrene-derivatives, but with solution access (solvent, ion, and reactant access) still readily provided by channels oriented parallel to an underlying planar electrode.

Anhydride-Terminated Solid-State Carbon Dots with Bright Orange Emission Induced by Weak Excitonic Electronic Coupling.

In this work, fluorescent solid carbon dots (CDs) welcome a new member, namely anhydride-terminated CDs, which have a photoluminescence quantum yield (PLQY) of 28% for orange-emitted CDs at 580 nm in powder form. For the first time, we revealed that the electronic coupling of the functional groups should be a crucial factor affecting the optical properties of solid CDs. Due to the negligible hydrogen bonding interaction between the anhydride groups, the electronic coupling of excitons between neighboring anhydride groups is weak, leading to a high PLQY of 28% and an immobile emission peak at 580 nm in solid state. Anhydride-terminated CDs can be partly converted into carboxyl-terminated CDs after dispersion in ethanol. However, the strong electronic coupling of carboxyl groups at high concentration generates the stacking mode of J-aggregates, giving rise to a red-shifted emission from 450 to 515 nm as well as quenched fluorescence in solid state. In comparison, a useful blue emission for solid-state CDs occurs from low sp2 hybridized carbon atoms, which possess weak electronic coupling and a stationary emission band at 450 nm in both solution and solid state. By adjusting the feed ratio of the reactants, the relevant intensities between the emission from low sp2 hybridized carbon atoms at 450 nm and the emission from anhydride groups at 580 nm can be controlled. As a result, single-component anhydride-terminated CD powder with tunable emission color from orange to white light can be achieved. As-prepared anhydride-terminated CDs can be used for fabricating light-emitting diodes (LEDs), white LEDs, and luminescent solar concentrators (LSCs).

Unexpected role of electronic coupling between host redox centers in transport kinetics of lithium ions in olivine phosphate materials.

The discrepancy between the trend in the diffusion coefficient of a lithium ion (DLi+) and that in the activation energy of ion hopping signals hidden factors determining ion transport kinetics in layered olivine phosphate materials (LiMPO4). Combining density functional theory (DFT) calculations and the Landau–Zener electron transfer theory, we unravel this hidden factor to be the electronic coupling between redox centers of the host materials. The ion transport process in LiMPO4 is newly described as an ion-coupled electron transfer (ET) reaction, where the electronic coupling effect on DLi+ is considered by incorporating the electronic transmission coefficient into the rate constant of the transfer reaction. The new model and DFT calculation results rationalize experimental values of DLi+ for various LiMPO4 (M = Fe, Mn, Co, Ni) materials, which cannot be understood solely by the calculated activation barrier of ion hopping. Interestingly, the electronic coupling between host redox centers is found to play an essential role. Particularly, the sluggish ion mobility in LiFePO4 is due to a very weak electronic coupling. The obtained insights imply that one can improve the rate performance of intercalation materials for metal-ion batteries through modifying the electronic coupling between redox centers of host materials.

Zinc phthalocyanine absorbance in the near-infrared with application for transparent and colorless dye-sensitized solar cells

Transparent and colorless solar cells are attractive new photovoltaic devices as they could bring new opportunities to harness sunlight energy and particularly for their integrations in windows. In this work, a new zinc phthalocyanine was synthesized and investigated as sensitizer in dye sensitized solar cell (DSSC) for this purpose. The zinc phthalocyanine features a benzoic acid anchoring group and six thio(4-tertbutylphenyl) substituents in position alpha of the phtalocyanine. The dye was characterized by absorption and emission spectroscopy and by electrochemistry. The physico-chemical properties show that the dye fulfills the criteria for such an application. A detailed computational study indicates that the electronic communication with TiO2 conduction is weak owing to the absence of overlapping of the wavefunctions of the dye with those of the TiO2 semiconductor. The photovoltaic performances of the zinc phthalocyanine were measured in TiO2 based DSSC and revealed inefficient electron injection and certainly explained by the weak electronic coupling of the 2 dye with TiO2 that limits electron injection efficiency. Strategy is proposed to make better performing sensitizers.

Peri-N-amine-perylenes, with and without phenyl bridge: Photophysical studies and their OLED applications

Donor-bridge-acceptor framework has been studied widely for their detailed photophysical properties with the aim of efficient long range charge transfer. Carbazole attached with electron acceptors has been used for charge transfer properties, thermally activated delayed fluorescence, exciton dynamics etc. In this study, we synthesized donor–acceptor dyads of seconday amine (carbazole and diphenyl amine) attached to perylene through nitrogen, with phenyl (P-Ph-N-CBZ and P-Ph-N-BP) and without phenyl (P-N-CBZ and P-N-BP). Further their detailed photophysical and electroluminescent properties are discussed. P-N-BP is known and is used as standard in this work. DFT studies show nearly orthogonal geometry of P-N-CBZ with the dihedral angle of ∼ 71° between the planes of perylene and carbazole. For P-Ph-N-BP and P-Ph-N-CBZ, the perylene and amines are adopting almost co-planar geometries. Emission spectra of P-Ph-N-CBZ and P-N-CBZ in dichloromethane are structural with clear vibronic features while for P-Ph-N-BP and P-N-BP, the emission is structureless and broad indicating prominent electronic coupling between molecular orbitals of donor and acceptor in the latter case. Fluorescence quantum yields of phenyl-linked dyads are found to be higher than directly linked perylene-amine derivatives. High quantum yield (0.79) in non-polar hexane and polar DMSO (0.66) is observed for P-Ph-N-CBZ. It is interesting to note that the fluorescence lifetimes of these dyads are increasing while fluorescence quantum yields are decreasing with increasing polar solvents, suggesting that the emission has a significant contribution from the 1CT state. Dipole moments estimated from DFT studies and photophysical methods are higher for phenyl-linked dyads than those directly attached which is also consistent with their solvatochromism properties. Weaker electronic coupling in phenyl-linked dyads resulted due to the long distance between donor and acceptor in phenyl-linked dyads. Furthermore application in OLEDs was shown for P-Ph-N-CBZ and P-Ph-N-BP. OLEDs of P-Ph-N-BP showed a peak emission at 568 nm resulting in an amber device. A high luminance of 4.3 × 103 Cd/m2 at a current density of 100 mA/cm2 and a maximum EQE of 4.2% with a low turn on volatage of ∼ 4 V was obtained for these devices. Thus, our results show that weaker charge transfer takes place in perylene based donor–acceptor dyads resulting in bright OLED devices.

Photoinduced Energy-Level Realignment at Interfaces between Organic Semiconductors and Metal-Halide Perovskites

In contrast to the common conception that the interfacial energy-level alignment is affixed once the interface is formed, we demonstrate that heterojunctions between organic semiconductors and metal-halide perovskites exhibit huge energy-level realignment during photoexcitation. Importantly, the photoinduced level shifts occur in the organic component, including the first molecular layer in direct contact with the perovskite. This is caused by charge-carrier accumulation within the organic semiconductor under illumination and the weak electronic coupling between the junction components.