A theoretical study on π-stacking and ferromagnetism of the perylene diimide radical anion dimer and tetramer.

Ferromagnetism is rare in pure organic materials. Recently, the perylene diimide radical anion (PDI-) salt prepared through solvothermal reduction by hydrazine hydrate has shown room-temperature ferromagnetism in our work [Jiang et al., Adv. Mater., 2022, 34, 2108103]. Based on this, herein we conduct a theoretical study based on density functional theory (DFT) to reveal the stacked geometries between two NH4PDI monomers for low-spin (LS) and high-spin (HS) states and their magnetic exchange interactions (JAB) using Yamaguchi's approximate spin projection. It is observed that the pancake-bonded dimer of NH4PDI is the most stable pimer compared to others on both LS and HS potential energy surfaces. A transition of magnetic properties from strong antiferromagnetic (-1333.9 cm-1) to moderate ferromagnetic (67.0 cm-1) appears after increasing the interplanar distance between monomers and their relative rotation angle to access the HS state. According to energy decomposition analysis, the enhanced hydrogen bond formation and decrease of Pauli repulsion is able to counteract the decrease of attraction induced by electron correlation after accessing the HS state. Stacking patterns of exchange-coupled chain consisting of the NH4PDI tetramer are obtained for the HS state after geometry optimization of the structure constructed by two most stable HS pimers. The exchange interactions (51.8 cm-1, 381.2 cm-1 and 53.2 cm-1) between adjacent NH4PDI monomers are ferromagnetic in the HS state, which is in accordance with the experimentally observed room-temperature ferromagnetism.

Predicting the Feasibility of Copper(I)-Catalyzed Alkyne-Azide Cycloaddition Reactions Using a Recurrent Neural Network with a Self-Attention Mechanism.

The copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction, a major click chemistry reaction, is widely employed in drug discovery and chemical biology. However, the success rate of the CuAAC reaction is not satisfactory as expected, and in order to improve its performance, we developed a recurrent neural network (RNN) model to predict its feasibility. First, we designed and synthesized a structurally diverse library of 700 compounds with the CuAAC reaction to obtain experimental data. Then, using reaction SMILES as input, we generated a bidirectional long-short-term memory with a self-attention mechanism (BiLSTM-SA) model. Our best prediction model has total accuracy of 80%. With the self-attention mechanism, adverse substructures responsible for negative reactions were recognized and derived as quantitative descriptors. Density functional theory investigations were conducted to provide evidence for the correlation between bromo-α-C hybrid types and the success rate of the reaction. Quantitative descriptors combined with RDKit descriptors were fed to three machine learning models, a support vector machine, random forest, and logistic regression, and resulted in improved performance. The BiLSTM-SA model for predicting the feasibility of the CuAAC reaction is superior to other conventional learning methods and advances heuristic chemical rules.

Lead-Based Metal-Organic Framework with Stable Lithium Anodic Performance.

A microporous Pb-based metal-organic framework (MOF) [Pb(4,4'-ocppy)2]·7H2O (Pb-MOF) has been constructed from 4-(4-carboxyphenyl)pyridine N-oxide and Pb(NO3)2. Structural analysis reveals that the Pb-MOF possesses three-dimensional framework with a one-dimensional rhombic channel. When tested as a lithium-ion battery anode, a reversible lithium storage capacity of 489 mAh g-1 was maintained after 500 cycles at 100 mA g-1 as well as excellent cycling stability. The superior electrochemical performance may be derived from the sustenance of the Pb-MOF framework and compositional features of the organic moiety.

A DFT study on the mechanism of photoselective catalytic reduction of 4-bromobenzaldehyde in different solvents employing an OH-defected TiO2 cluster model.

Density functional theory calculations are employed to study the mechanism of photoselective catalytic reduction of 4-bromobenzaldehyde (4-BBA) in acetonitrile and in ethanol solvents. A totally relaxed Ti3O9H6 cluster model is proposed to represent titanium dioxide (TiO2) surfaces. The reduction selectivity of an adsorbed 4-BBA molecule on Ti3O9H6 has been investigated. Owing to the difference in the proton and H atom donating capabilities between explicit CH3CN and C2H5OH solvent molecules, the photocatalytic reduction of 4-BBA is the debromination process in acetonitrile, whereas in ethanol it is the carbonyl reduction process. Therefore 4-BBA can be selectively reduced to benzaldehyde in acetonitrile and 4-bromobenzyl alcohol in ethanol, respectively. Our computational results have verified the reaction mechanism proposed by experiments and show that the debromination of 4-BBA would be efficient if both 4-BBA and Ti3O9H6 have an extra photoelectron. The Ti3O9H6 cluster, playing a role as a hydrogen source and a bridge to transfer photoelectrons from bulk TiO2, would have potential to be an ideal molecular model for understanding photocatalytic reactions on the TiO2 surface.

Achieving Ultra-Narrow-Band Deep-Red Electroluminescence By a Soliton-type Dye Squaraine.

Due to the soliton-like electronic structural characteristics, cyanine dyes typically exhibit spectral behaviors such as large molar extinction coefficients, narrow spectra, and high fluorescence efficiency. However, their extensive applications as emitters in electroluminescence are largely ignored due to their serious emission quenching in the aggregation state. Herein, it is reported a squaraine dye (a type of cyanine) SQPhEt. At different solution concentrations, the unusual decrease in full-width at half-maxima (FWHM) with increasing Stokes shift indicates the fluorescence quenching of SQPhEt in the aggregated state is because of the strong self-absorption effect. A sensitized device structure can help to reduce the doping concentration of dye, which can effectively suppress self-absorption. Benefitting from the large molar extinction coefficient of SQPhEt, even at low doping concentrations of 0.1 wt%, efficient Förster energy transfer can be achieved. The corresponding spin-coating sensitized device based on SQPhEt as the dopant exhibits favorable deep-red emission at 668 nm with a small FWHM of 0.10 eV.

Band-like transport in solution-processed perylene diimide dianion films with high Hall mobility.

It is crucial to prepare high-mobility organic polycrystalline film through solution processing. However, the delocalized carrier transport of polycrystalline films in organic semiconductors has rarely been investigated through Hall-effect measurement. This study presents a strategy for building strong intermolecular interactions to fabricate solution-crystallized p-type perylene diimide (PDI) dianion films with a closer intermolecular π-π stacking distance of 3.25 Å. The highly delocalized carriers enable a competitive Hall mobility of 3 cm2 V-1 s-1, comparable to that of the reported high-mobility organic single crystals. The PDI dianion films exhibit a high electrical conductivity of 17 S cm-1 and typical band-like transport, as evidenced by the negative temperature linear coefficient of mobility proportional to T-3/2. This work demonstrates that, as the intermolecular π-π interactions become strong enough, they will display high mobility and conductivity, providing a new approach to developing high-mobility organic semiconductor materials.

Chemical reaction-transport model of oxidized diethylzinc based on quantum mechanics and computational fluid dynamics approaches.

We developed and studied a chemical reaction-transport model for the production of zinc oxide (ZnO) with diethylzinc (DEZn) and oxygen (O2). It was confirmed that a large number of ZnO particles were generated during the growth process by testing the internal particles of the cavity by X-ray diffraction. The formation of Zn3O3 in the gas phase reaction was simulated using density functional theory, and the effect of nucleation and formation of nanoparticles on the growth of the films was revealed. We also speculate that the adsorption of Zn-containing gas on the wall is the main route by which a ZnO film is formed. The mechanism calculated by quantum chemistry was applied in computational fluid dynamics (CFD) simulations using Fluent14.0 software, and the concentration distribution and gas reaction path of the reaction chamber were calculated and analyzed. Finally, a 9 gas phase reaction model and an 8 surface reaction model were established. Together with the transport model, a complete chemical reaction-transport reaction model was constructed for the ZnO-MOCVD cavity. The validity of the model was verified, and the optimum temperature range of DEZn and oxygen-stabilized growth of ZnO films was determined to be 673-873 K. Using the results of the chemical reaction transport model, the geometry and operation parameters of the reactor can be optimized to improve the characteristics of the epitaxial layer.