Efficient and Accurate Estimation of Electronic Polarization Energies for Organic Semiconductors: An Embedding Charge Quantum Mechanics/Continuum Dielectric Model.

Electronic polarization plays a pivotal role in determining the molecular energy levels of organic semiconductors (OSCs) in the condensed phase. However, accurate estimation of the electronic polarization energy is a challenging task due to the intricate imbalance between the precision and efficiency. In this work, we have developed an embedding charge quantum mechanics/continuum dielectric (EC-QM/CD) model, which enables quantitative evaluation of the ionization potential (IP), electron affinity (EA), and polarization energy in both crystalline and amorphous solids for OSCs. The benchmark calculations on both p-type OSCs of oligoacenes and n-type OSCs of A-D-A small-molecule acceptors show that the values of IP, EA, and polarization energy obtained by EC-QM/CD are in good accordance with the experimental measurements or the results by high-precision methods, while the computational costs are substantially reduced. Given its balance between the accuracy and efficiency, the EC-QM/CD model exhibits considerable potential to broaden the applications in the field of OSCs, for instance, high-throughput screening by using solid-state energy levels or polarization energies as critical descriptors.

Investigation of the Degradation of LiPF6- in Polar Solvents through Deep Potential Molecular Dynamics.

The nonaqueous electrolyte based on lithium hexafluorophosphate (LiPF6) is the dominant liquid electrolyte in lithium-ion batteries (LIBs). However, trace protic impurities, including H3O+, alcohols, and hydrofluoric acid (HF), can trigger a series of side reactions that lead to rapid capacity fading in high energy density LIBs. It is worth noting that this degradation process is highly dependent on the polarity of the solvents. In this work, a deep potential (DP) model is trained with a certain commercial electrolyte formula through a machine learning method. H3O+ is anchored with polar solvents, making it difficult to approach the PF6-, and suppressing the degradation process quickly at room temperature. Control experiments and simulations at different temperatures or concentrations are also performed to verify it. This work proposes a precise model to describe the solvation structure quantitatively and offers a new perspective on the degradation mechanism of PF6- in polar solvents.

Constrained Hybrid Monte Carlo Sampling Made Simple for Chemical Reaction Simulations.

Most electrochemical reactions should be studied under a grand canonical ensemble condition with a constant potential and/or a constant pH value. Free energy profiles provide key insights into understanding the reaction mechanisms. However, many molecular dynamics (MD)-based theoretical studies for electrochemical reactions did not employ an exact grand canonical ensemble sampling scheme for the free energy calculations, partially due to the issues of discontinuous trajectories induced by the particle-number variations during MD simulations. An alternative statistical sampling approach, the Monte Carlo (MC) method, is naturally appropriate for the open-system simulations if we focus on the thermodynamic properties. An advanced MC scheme, the hybrid Monte Carlo (HMC) method, which can efficiently sample the configurations of a system with large degrees of freedom, however, has limitations in the constrained-sampling applications. In this work, we propose an adjusted constrained HMC method to compute free energy profiles using the thermodynamic integration (TI) method. The key idea of the method for handling the constraint in TI is to integrate the reaction coordinate and sample the rest degrees of freedom by two types of MC schemes, the HMC scheme and the Metropolis algorithm with unbiased trials (M(RT)2-UB). We test the proposed method on three different systems involving two kinds of reaction coordinates, which are the distance between two particles and the difference of particles' distances, and compare the results to those generated by the constrained M(RT)2-UB method serving as benchmarks. We show that our proposed method has the advantages of high sampling efficiency and convenience of implementation, and the accuracy is justified as well. In addition, we show in the third test system that the proposed constrained HMC method can be combined with the path integral method to consider the nuclear quantum effects, indicating a broader application scenario of the sampling method reported in this work.

Unraveling the Dynamic Correlations between Transition Metal Migration and the Oxygen Dimer Formation in the Highly Delithiated LixCoO2 Cathode.

The voltage-window expansion can increase the practical capacity of LixCoO2 cathodes, but it would lead to serious structural degradations and oxygen release induced by transition metal (TM) migration. Therefore, it is crucial to understand the dynamic correlations between the TM migration and the oxygen dimer formation. Here, machine-learning-potential-assisted molecular dynamics simulations combined with enhanced sampling techniques are performed to resolve the above question using a representative CoO2 model. Our results show that the occurrence of the Co migration exhibits local characteristics. The formation of the Co vacancy cluster is necessary for the oxygen dimer generation. The introduction of the Ti dopant can significantly increase the kinetic barrier of the Co ion migration and thus effectively suppress the formation of the Co vacancy cluster. Our work reveals atomic-scale dynamic correlations between the TM migration and the oxygen sublattice's instability and provides insights about the dopant's promotion of the structural stability.

Impact of the Local Environment on Li Ion Transport in Inorganic Components of Solid Electrolyte Interphases.

The spontaneously formed passivation layer, the solid electrolyte interphase (SEI) between the electrode and electrolyte, is crucial to the performance and durability of Li ion batteries. However, the Li ion transport mechanism in the major inorganic components of the SEI (Li2CO3 and LiF) is still unclear. Particularly, whether introducing an amorphous environment is beneficial for improving the Li ion diffusivity is under debate. Here, we investigate the Li ion diffusion mechanism in amorphous LiF and Li2CO3 via machine-learning-potential-assisted molecular dynamics simulations. Our results show that the Li ion diffusivity in LiF at room temperature cannot be accurately captured by the Arrhenius extrapolation from the high temperature (>600 K) diffusivities (difference of ∼2 orders of magnitude). We reveal that the spontaneous formation of Li-F regular tetrahedrons at low temperatures (<500 K) leads to an extremely low Li ion diffusivity, suggesting that designing an amorphous bulk LiF-based SEI cannot help with the Li ion transport. We further show the critical role of Li2CO3 in suppressing the Li-F regular tetrahedron formation when these two components of SEIs are mixed. Overall, our work provides atomic insights into the impact of the local environment on Li ion diffusion in the major SEI components and suggests that suppressing the formation of large-sized bulk-phase LiF might be critical to improve battery performance.

Toward Quantifying the Relation between Exciton Binding Energies and Molecular Packing.

Reducing the exciton binding energy Eb of organic photoactive materials is critical to minimize the energy loss and improve the photovoltaic efficiency of organic solar cells. However, the relation between the Eb and molecular packing is not well understood. Herein, the Eb in the crystals of a series of A-D-A type nonfullerene acceptors with different lengths of alkyl side chains has been examined by self-consistent quantum mechanics/embedded charge calculations. The variation of molecular packing induced by the different alkyl chains can have an important impact on the polarization effect of charge carriers and thereby the Eb. More interestingly, the Eb values are found to be linearly increased with the ratio of the void fraction vs the packing coefficient of molecular backbones in the solid crystals. Owing to the smallest ratio, a remarkable low Eb of several tens of meV is achieved for the acceptor with an optimal length of alkyl chains.

Surface-Plasmon-Mediated Alloying for Monodisperse Au-Ag Alloy Nanoparticles in Liquid.

Plasmonic noble-metal nanoparticles with broadly tunable optical properties and catalytically active surfaces offer a unique opportunity for photochemistry. Resonant optical excitation of surface-plasmon generates high-energy hot carriers, which can participate in photochemical reactions. Although the surface-plasmon-driven catalysis on molecules has been extensively studied, surface-plasmon-mediated synthesis of bimetallic nanomaterials is less reported. Herein, we perform a detailed investigation on the formation mechanism and colloidal stability of monodisperse Au-Ag alloy nanoparticles synthesized through irradiating the intermixture of Au nanochains and AgNO3 solution with a nanosecond pulsed laser. It is revealed that the Ag atoms can be extracted from AgNO3 solution by surface-plasmon-generated hot electrons and alloy with Au atoms. Particularly, the obtained Au-Ag alloy nanoparticles without any surfactants or ligands exhibit superior stability that is confirmed by experiments as well as DLVO-based theoretical simulation. Our work would provide novel insights into the synthesis of potentially useful bimetallic nanoparticles via surface-plasmon-medicated alloying.

Two-Channel Space Charge Transfer-Induced Thermally Activated Delayed Fluorescent Materials for Efficient OLEDs with Low Efficiency Roll-Off.

Enhancing the reverse intersystem crossing (RISC) process of thermally activated delayed fluorescent (TADF) emitters is an effective approach to realize efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off. In this work, we designed two novel TADF emitters, SAT-DAC and SATX-DAC, via a spiro architecture. Efficient maximum external quantum efficiencies (EQEs) of 22.6 and 20.9% with reduced efficiency roll-off (EQEs of 17.9 and 17.0% at 1000 cd m-2) were achieved via a "two-RISC-channel" strategy. X-ray diffraction shows close donor (D)/acceptor (A) spacing and suitable D/A orientation in crystals of the two emitters favoring both intra- and intermolecular through-space charge transfer (TSCT) processes. Transient photoluminescence decay measurements show that both emitters have two RISC channels leading to kISCT exceeding 106 s-1. These results suggest that the "two-RISC-channel" design can be a novel approach for enhancing performance of TADF emitters, in particular at high excitation densities.

Reducing the Singlet-Triplet Energy Gap by End-Group π-π Stacking Toward High-Efficiency Organic Photovoltaics.

To improve the power conversion efficiencies for organic solar cells, it is necessary to enhance light absorption and reduce energy loss simultaneously. Both the lowest singlet (S1) and triplet (T1) excited states need to energertically approach the charge-transfer state to reduce the energy loss in exciton dissociation and by triplet recombination. Meanwhile, the S1 energy needs to be decreased to broaden light absorption. Therefore, it is imperative to reduce the singlet-triplet energy gap (ΔEST ), particularly for the narrow-bandgap materials that determine the device T1 energy. Although maximizing intramolecular push-pull effect can drastically decrease ΔEST , it inevitably results in weak oscillator strength and light absorption. Herein, large oscillator strength (≈3) and a moderate ΔEST (0.4-0.5 eV) are found for state-of-the-art A-D-A small-molecule acceptors (ITIC, IT-4F, and Y6) owing to modest push-pull effect. Importantly, end-group π-π stacking commonly in the films can substantially decrease the S1 energy by nearly 0.1 eV, but the T1 energy is hardly changed. The obtained reduction of ΔEST is crucial to effectively suppress triplet recombination and acquire small exciton dissociation driving force. Thus, end-group π-π stacking is an effective way to achieve both small energy loss and efficient light absorption for high-efficiency organic photovoltaics.

Clustering-Triggered Efficient Room-Temperature Phosphorescence from Nonconventional Luminophores.

Pure organic room-temperature phosphorescence (RTP) and luminescence from nonconventional luminophores have gained increasing attention. However, it remains challenging to achieve efficient RTP from unorthodox luminophores, on account of the unsophisticated understanding of the emission mechanism. Herein, we propose a strategy to realize efficient RTP in nonconventional luminophores through incorporation of lone pairs together with clustering and effective electronic interactions. The former promotes spin-orbit coupling and boosts the consequent intersystem crossing, whereas the latter narrows energy gaps and stabilizes the triplets, thus synergistically affording remarkable RTP. Experimental and theoretical results of urea and its derivatives verify the design rationale. Remarkably, RTP from thiourea solids with unprecedentedly high efficiency of up to 24.5 % is obtained. Further control experiments testify the crucial role of through-space delocalization on the emission. These results will spur the future fabrication of nonconventional phosphors and advance the understanding of the underlying emission mechanism.

Angular-Fused Dithianaphthylquinone Derivative: Selective Synthesis, Thermally Activated Delayed Fluorescence Property, and Application in Organic Light-Emitting Diode.

A novel angular-fused dithianaphthylquinone derivative, f-TX-TPA, was designed and selectively synthesized. The regioselectivity of angular-fused reaction was interpreted by theoretical calculations. The f-TX-TPA compound displayed excellent thermally activated delayed fluorescence property. Moreover, the organic light-emitting diodes (OLEDs) using f-TX-TPA as an emitter exhibited a high external quantum efficiency of 15.9%. These results indicated that angular-fused dithianaphthylquinone derivatives could have great potential in the application of high-efficiency OLEDs.

Phthalimide-based "D-N-A" emitters with thermally activated delayed fluorescence and isomer-dependent room-temperature phosphorescence properties.

Phthalimide-based "D-N-A" emitters o-AI-Cz, m-AI-Cz and p-AI-Cz showed TADF and RTP properties due to their small ΔEST in both film and crystalline states. In particular, o-AI-Cz exhibited an ultralong RTP with a lifetime of 602 ms in air and remarkable afterglow, which could allow it to be used as a security ink for application in anti-counterfeiting materials. Moreover, o-AI-Cz showed intense intramolecular interaction between the donor and the acceptor subunits, while p-AI-Cz could form regular hexagonal pores with a diameter of 13.171 Å in the solid state, which might result in their different RTP properties.

Inorganic-organic CdSe-diethylenetriamine nanobelts for enhanced visible photocatalytic hydrogen evolution.

Inorganic-organic hybrid nanomaterials, with excellent chemical and physical properties and technology applications, have attracted much attention in many fields. In the photocatalytic field, it is still a problem to find a stable, adjustable morphology and band gap and effective photocatalyst in utilizing solar energy conversion to hydrogen (H2) to solve the energy crisis. Herein, with the assistance of diethylenetriamine (DETA), the novel inorganic-organic CdSe-DETA hybrids with different morphology and adjustable band gap have been synthesised via simple microwave hydrothermal method. The morphological transformation mechanism involves the consumption of organic components controlled by the mixed precursor and subsequent self-assembly of residual inorganic components (CdSe). Under the visible light irradiation (λ > 420 nm), CdSe-18DETA nanobelt, showed the best photocatalytic H2 production activity (5.75 mmol·g-1·h-1), which is 3.03 times greater than that of pure CdSe (1.90 mmol·g-1·h-1). Moreover, after four cycles, the photocatalytic H2 production activity can still remain 91.27% of initial value, which indicates its good photocatalytic stability. Our results provide a promising approach for designing visible-light photocatalysts with efficient electron-hole separation and adjustable morphology and band gap.

Intermolecular Interaction-Induced Thermally Activated Delayed Fluorescence Based on a Thiochromone Derivative.

Exploration of new extrinsic ways to modulate thermally activated delayed fluorescence (TADF) to achieve high exciton utilization efficiency in organic light-emitting diodes (OLEDs) is highly desirable. A new thiochromone derivative 2,3-bis(4-(9 H-carbazol-9-yl)phenyl)-4 H-thiochromen-4-1,1-dioxide (THI-PhCz) with tunable photophysical properties from crystals to amorphous states is reported. THI-PhCz shows molecular-packing-dependent TADF in different aggregation states based on the differences of intermolecular interactions. Furthermore, it is observed that THI-PhCz doped in amorphous films of different hosts also shows host-dependent TADF with a short delay lifetime (108 ns), which is interpreted as the effect of host-guest intermolecular interaction on the 3CT state except for the effect on the 1CT state in reported references. This work provides a new perspective for generation of TADF by tuning intermolecular interactions in crystals and amorphous films except for molecular design, which is expected to contribute in achieving low-efficiency roll-off OLEDs with effective exciton utilization efficiency.

Design of Efficient Exciplex Emitters by Decreasing the Energy Gap Between the Local Excited Triplet (3LE) State of the Acceptor and the Charge Transfer (CT) States of the Exciplex.

A series of thermally activated delayed fluorescence (TADF) exciplex based on the TX-TerPy were constructed. The electronic coupling between the triplet local excited states (3LE) of the donors and acceptor and the charge transfer states had a great influence on the triplet exciton harvesting and ΦPL. Herein, based on this strategy, three donor molecules TAPC, TCTA, and m-MTDATA were selected. The local triplet excited state (3LE) of the three donors are 2.93, 2.72 and 2.52 eV in pure films. And the 3LE of TX-TerPy is 2.69 eV in polystyrene film. The energy gap between the singlet charge transfer (1CT) states of TAPC:TX-TerPy (7:1), TCTA:TX-TerPy (7:1) and the 3LE of TX-TerPy are 0.30 eV and 0.20 eV. Finally, the ΦPL of TAPC:TX-TerPy (7:1) and TCTA:TX-TerPy (7:1) are 65.2 and 69.6%. When we changed the doping concentration of the exciplex from 15% to 50%, the ratio of the triplet decreased, and ΦPL decreased by half, perhaps due to the increased energy gap between 1CT and 3LE. Therefore, optimizing the 1CT, 3CT, and 3LE facilitated the efficient exciplex TADF molecules.

Sonic hedgehog improves delayed wound healing via enhancing cutaneous nitric oxide function in diabetes.

Sonic hedgehog (SHH) plays an important role in postnatal tissue repair. The present study tested the hypothesis that impaired SHH pathway results in delayed wound healing by suppressing cutaneous nitric oxide (NO) function in type 1 diabetes. Adult male C57/B6 mice and streptozotocin (STZ)-induced type 1 diabetic mice were used. Although cutaneous SHH and Patched-1 (Ptc-1 encoded by PTCH, PTCH 1) proteins were increased significantly on day 4 after wounding compared with day 0 in normal mice, both were decreased significantly in STZ-induced diabetic mice. Topical application of SHH restored wound healing delay in STZ-induced diabetic mice, with a concomitant augmentation of both cutaneous constitutive nitric oxide synthase (NOS) activity and nitrite level. The effects of SHH on wound healing and cutaneous NO function were markedly inhibited by SHH receptor inhibitor cyclopamine. After 24-h treatment in vitro, SHH (5-20 microg/ml) significantly increased cutaneous endothelial NOS protein expression, NOS activity and NO level in normal mice and STZ-induced diabetic mice in a concentration-dependent manner, an effect that was blunted by cyclopamine and NOS inhibitor N(omega)-nitro-L-arginine methyl ester. The phosphatidylinositol 3-kinase inhibitor LY-294002 significantly blunted the increase of NOS activity and NO level induced by SHH treatment in human umbilican vein endothelial cells. These results demonstrate that the SHH pathway is activated in a normal wound, and its reduction results in impaired NO function and wound healing in diabetes. Strategies aimed at augmenting the endogenous SHH pathway may provide an effective means in ameliorating delayed diabetic wound healing.

Simvastatin inhibits leptin-induced hypertrophy in cultured neonatal rat cardiomyocytes.

AIM: To test the hypothesis that statins inhibit leptin-induced hypertrophy in cultured neonatal rat cardiomyocytes. METHODS: Cultured neonatal rat cardiomyocytes were used to evaluate the effects of simvastatin on leptin-induced hypertrophy. Intracellular reactive oxygen species (ROS) levels were determined by using 2',7'-dichlorofluorescein diacetate (DCF-DA) fluorescence. Total intracellular RNA and cell protein content, which serve as cell proliferative markers, were assayed by using propidium iodide (PI) fluorescence and the Bio-Rad DC protein assay, respectively. The cell surface area, an indicator of cell hypertrophy, was quantified by using Leica image analysis software. RESULTS: After 72 h treatment, leptin markedly increased RNA levels, cell surface area, and total cell protein levels in cardiomyocytes, which were significantly inhibited by simvastatin or catalase treatment. ROS levels were significantly elevated in cardiomyocytes treated with leptin for 4 h compared with those cells without leptin treatment. The increase in ROS levels in cardiomyocytes induced by leptin was reversed by treatment with simvastatin and catalase. CONCLUSION: Simvastatin inhibits leptin-induced ROS-mediated hypertrophy in cultured neonatal rat cardiac myocytes. Statin therapy may provide an effective means of improving cardiac dysfunction in obese humans.