Molecular structure, spectroscopy, and photoinduced kinetics in trinuclear cyanide bridged complex in solution: a first-principles perspective

Enabling long-cycling aqueous sodium-ion batteries via Mn dissolution inhibition using sodium ferrocyanide electrolyte additive

Aqueous sodium-ion batteries (AIBs) are promising candidates for large-scale energy storage due to their safe operational properties and low cost. However, AIBs have low specific energy (i.e., <80 Wh kg^-1) and limited lifespans (e.g., hundreds of cycles). Mn-Fe Prussian blue analogues are considered ideal positive electrode materials for AIBs, but they show rapid capacity decay due to Jahn-Teller distortions. To circumvent these issues, here, we propose a cation-trapping method that involves the introduction of sodium ferrocyanide (Na₄Fe(CN)₆) as a supporting salt in a highly concentrated NaClO₄-based aqueous electrolyte solution to fill the surface Mn vacancies formed in Fe-substituted Prussian blue Na_1.58Fe_0.07Mn_0.97Fe(CN)₆ · 2.65H₂O (NaFeMnF) positive electrode materials during cycling. When the engineered aqueous electrolyte solution and the NaFeMnF-based positive electrode are tested in combination with a 3, 4, 9, 10-perylenetetracarboxylic diimide-based negative electrode in a coin cell configuration, a specific energy of 94 Wh kg^-1 at 0.5 A g^-1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 73.4% after 15000 cycles at 2 A g^-1 are achieved.

Linear fractional charge behavior in density functional theory through dielectric tuning of conductor-like polarizable continuum model

A property of exact density functional theory is linear fractional charge behavior as electrons are added or removed from a molecule. Typical density functional approximations (DFAs) exhibit delocalization error, which overstabilizes this fractional charge. Conversely, solvent corrections have been shown to erroneously destabilize this fractional charge. This work will show that an implicit solvent correction with a tuned dielectric can be used as an ad hoc correction to offset the delocalizing character of DFAs and achieve linear fractional charge behavior. While desirable, in principle, we find that this linear charge behavior degrades the vertical ionization energies reported by DFAs. Our results reveal that the localizing character of the solvent correction and the Hartree-Fock (HF) exchange offset each other. This helps explain the decreased ratios of HF exchange to DFA exchange in long-range hybrid tuning studies that use a solvent correction.

Electromagnetic absorbers with Schottky contacts derived from interfacial ligand exchanging metal-organic frameworks

Various types of polycrystals have been regarded as excellent electromagnetic (EM) microwave absorbents, while differentiated heterointerfaces among grains usually manipulate conductive loss and polarization relaxation, especially interfacial polarization. Herein, polar facets that dominated the optimization of EM attenuation were clarified by carefully designing polycrystalline Schottky junctions with metal-semiconductor contacts for the first time. An ingenious ligand exchange technique was utilized to construct Zn-MOF (ZIF-L) precursors for Fe-ZnO polycrystals, in which Fe-containing Fe(CN)₆^3- etching ligand acted as metallic source in Schottky junctions. By adjusting the Schottky contacts in polycrystals, the enhanced grain boundaries mainly induced stronger interfacial polarization and affected the microcurrent lightly. This is because Schottky barriers can cause local charge accumulation on heterointerfaces for polarization relaxation. Additionally, the coexistence of Zn and O vacancies brought a lot of lattice defects and distortions for dipole polarization. Thus, optimal EM wave absorbability was obtained by polycrystals with 8 h ligand exchange and an effective absorption band reaching 4.88 GHz. This work can provide guidance for designing advanced polycrystalline EM absorption materials and also highlight the mechanism and requirement of Schottky junctions dominating polarization.

Unraveling the Mechanism of Near-Infrared Thermally Activated Delayed Fluorescence of TPA-Based Molecules: Effect of Hydrogen Bond Steric Hindrance

A recently synthesized novel molecule (named CAT-1) exhibits intriguing near-infrared (NIR) thermally activated delayed fluorescence (TADF) close to 1000 nm wavelength; however, the mechanism behind these intrinsic properties is not fully understood. Herein, we unravel that the fluorescence emission spectrum with a broad wavelength range (770-950 nm) of CAT-1 is primarily induced by hydrogen bond steric hindrance based on density functional theory and Marcus theory. It is found that the hydrogen bond steric hindrance plays a critical role in inhibiting the twist of the configuration of different excited states, which leads to the minor driving force for fast electron trapping between the excited states, as well as small internal reorganization energy caused by less changed geometric configuration. Furthermore, such steric hindrance will cause a more distorted plane, resulting in a less favorable electron delocalization. A faster reverse intersystem crossing (RISC) rate is then obtained due to the nearly unchanged conformation between excited states caused by steric hindrance, although the spin-orbit coupling is small. Consequently, the NIR TADF with a longer wavelength can be emitted in CAT-1. This work shows that the hydrogen bond steric hindrance can fine-tune the electronic interactions of the donor and acceptor units to control the TADF.

Cyanide Bridged Platinum-Iron Complexes as Cisplatin Prodrug Systems: Design and Computational Study

The potential role of cyanide-bridged platinum-iron complexes as an anti-cancer Pt(IV) prodrug is studied. We present design principles of a dual-function prodrug that can upon reduction dissociate and release concurrently six cisplatin units and a ferricyanide anion per prodrug unit. The prodrug molecule is a unique complex of hepta metal centers consisting of a ferricyanide core with six Pt(IV) centers each bonded to the Fe(III) core through a cyano ligand. The functionality of the prodrug is addressed through density functional theory (DFT) calculations.

Enhanced dielectricity coupled to spin-crossover in a one-dimensional polymer iron(ii) incorporating tetrathiafulvalene

A concerted bending–flattening motion of the redox-active TTF within constructed one-dimensional Fe^II–TTF–Schiff-base chain with bridging 4,4′-bpy enhances the dielectric constant coupled to its spin-crossover transition above room temperature.

In designing multifunctional materials for potential switches that can be used as memory devices, the high-spin (HS) to low-spin (LS) crossover (SCO) one-dimensional polymer, [Fe^II(L)(4,4′-bpy)]_n, was constructed from a designed redox-active tetrathiafulvalene (TTF) functionalized Schiff-base and the ditopic linker 4,4′-bipyridine (bpy). It exhibits an 8 K hysteretic SCO centred at T_1/2 = 325 K which is coupled to changes in its dielectric constant. The crystal structures above and below the transition temperature reveal similar parallel linear ···Fe–bpy–Fe–bpy··· chains displaying expansion of the Fe^II octahedron in the HS state. Density functional theory (DFT) calculations reveal a concerted electronic charge and spin change represented by the Mülliken charge of the Fe and the magnitude and direction of the dipole moment which substantiate the experimental observations.

Molecular-scale engineering of the charge-transfer excited states in non-covalently bound Zn–porphyrin and carbon fullerene based donor–acceptor complex

Tailoring charge-transfer through selective pyrrole ring hydrogenation in a novel Zn–porphyrin and PCBM based donor–acceptor complex has been investigated using quantum chemical computations.

Dielectric Screening Meets Optimally Tuned Density Functionals

A short overview of recent attempts at merging two independently developed methods is presented. These are the optimal tuning of a range-separated hybrid (OT-RSH) functional, developed to provide an accurate first-principles description of the electronic structure and optical properties of gas-phase molecules, and the polarizable continuum model (PCM), developed to provide an approximate but computationally tractable description of a solvent in terms of an effective dielectric medium. After a brief overview of the OT-RSH approach, its combination with the PCM as a potentially accurate yet low-cost approach to the study of molecular assemblies and solids, particularly in the context of photocatalysis and photovoltaics, is discussed. First, solvated molecules are considered, with an emphasis on the challenge of balancing eigenvalue and total energy trends. Then, it is shown that the same merging of methods can also be used to study the electronic and optical properties of molecular solids, with a similar discussion of the pros and cons. Tuning of the effective scalar dielectric constant as one recent approach that mitigates some of the difficulties in merging the two approaches is considered.

Directional Electron Transfer in Crystals of [CrCo] Dinuclear Complexes Achieved by Chirality-Assisted Preparative Method

The polarization switching mechanism is used in various devices such as pyroelectric sensors and memory devices. The change in polarization mostly occurs by ion displacement. The development of materials whose polarization switches via electron transfer in order to enhance operation speed is a challenge. We devised a synthetic and crystal engineering strategy that enables the selective synthesis of a [CrCo] heterometallic dinuclear complex with a polar crystal structure, wherein polarization changes stem from intramolecular charge transfer between Co and the ligand. Polarization can be modulated both by visible-light irradiation and temperature change. The introduction of chiral ligands was paramount to the successful polarization switching in the valence tautomeric compound. Mixing Cr and Co complexes with enantiopure chiral ligands resulted in the selective formation of only pseudosymmetric [CrCo] heterometallic complexes. Furthermore, the left-handed chiral ligands preferentially interacted with their right-handed counterparts, enabling molecules to form a polar crystal structure.

Achieving Predictive Description of Molecular Conductance by Using a Range-Separated Hybrid Functional

The conductance of molecular bridges tends to be overestimated by computational studies in comparison to measured values. While this well-established trend may be related to difficulties for achieving robust bridges, the employed computational scheme can also contribute to this tendency. In particular, caveats of the traditional functionals employed in first-principles-based calculations can lead to discrepancies reflected in exaggerated conductance. Here, we show that by employing a range-separated hybrid functional the calculated values are within the same order as the measured conductance for all four considered cases. On the other hand, with B3LYP, which is a widely used functional, the calculated values greatly overestimate the conductance (by about 1-2 orders of magnitude). The improved description of the conductance with a RSH functional builds on achieving a physically meaningful treatment of the quasi particles associated with the frontier orbitals.