Orbital Theory Research Articles

Nature and stability of the chemical bond in H3C-XHn (XHn = CH3, NH2, OH, F, Cl, Br, I).

We have quantum chemically analyzed the trends in bond dissociation enthalpy (BDE) of H3C-XHn single bonds (XHn = CH3, NH2, OH, F, Cl, Br, I) along three different dissociation pathways at ZORA-BLYP-D3(BJ)/TZ2P: (i) homolytic dissociation into H3C∙ + ∙XHn, (ii) heterolytic dissociation into H3C+ + -XHn, and (iii) heterolytic dissociation into H3C- + +XHn. The associated BDEs for the three pathways differ not only quantitatively but, in some cases, also in terms of opposite trends along the C-X series. Based on activation strain analyses and quantitative molecular orbital theory, we explain how these differences are caused by the profoundly different electronic structures of, and thus bonding mechanisms between, the resulting fragments in the three different dissociation pathways. We demonstrate that the nature and strength of a chemical bond are only fully defined when considering both (i) the molecule in which the bond exists and (ii) the fragments from which it forms or into which it dissociates.

Origin of 13C NMR chemical shifts elucidated based on molecular orbital theory: paramagnetic contributions from orbital-to-orbital transitions for the pre-α, α, β, α-X, β-X and ipso-X effects, along with effects from characteristic bonds and groups.

13C NMR chemical shifts (δ(C)) were analysed via MO theory, together with the origin, using σ d(C), σ p(C) and σ t(C), where C4- was selected as the standard for the analysis since σ p(C: C4-) = 0 ppm. An excellent relationship was observed between σ d(C) and the charges on C for (C4+, C2+, C0, C2- and C4-) and (C4-, CH2 2-, CH3 - and CH4). However, such a relationship was not observed for the carbon species other than those above. The occupied-to-unoccupied orbital (ψ i →ψ a ) transitions were mainly employed for the analysis. The origin was explained by the pre-α, α, β, α-X, β-X and ipso-X effects. The pre-α effect of an approximately 20 ppm downfield shift is theoretically predicted, and the observed α and β effects of approximately 10-15 ppm downfield shifts are well reproduced by the calculations, as are the variations in the α-X, β-X and ipso-X effects. Large downfield shifts caused by the formation of ethene (∼120 ppm), ethyne (∼60 ppm) and benzene (∼126 ppm) from ethane and carbonyl (∼146 ppm) and carboxyl (∼110 ppm) groups from CH3OH are also reproduced well by the calculations. The analysis and illustration of σ p(C) through the ψ i →ψ a transitions enables us to visualize the effects and to understand the δ(C) values for the C atoms in the specific positions of the species. The occupied-to-occupied orbital (ψ i →ψ j ) transitions are also examined. The theoretical investigations reproduce the observed results of δ(C). The origin for δ(C) and the mechanism are visualized, which allows us to image the process in principle. The role of C in the specific position of a compound in question can be more easily understood, which will aid in the development of highly functional compounds based on NMR.

Plasmon hybridization model in molecules: molecular jackhammers.

We recently demonstrated molecular plasmons in cyanine dyes for the conversion of photon energy into mechanical energy through a whole-molecule coherent vibronic-driven-action. Here we present a model, a molecular plasmon analogue of molecular orbital theory and of plasmon hybridization in metal nanostructures. This model describes that molecular plasmons can be obtained from the combination or hybridization of elementary molecular fragments, resulting in molecules with hybridized plasmon resonances in the electromagnetic spectrum. We applied our approach to the hybridization of the benzoindole and heptamethine fragments for understanding of the resonance frequencies in cyanines using UV-vis and Raman spectroscopy. The molecular plasmon resonances in cyanines are tunable by engineering molecular structure modifications and controlling the dielectric constant of the medium in which the cyanines are dissolved. We measured the plasmonicity index, an easy-to-use and powerful tool to predict and quantify if an organic molecule in solution is a molecular plasmon. This is done by analyzing the UV-vis spectrum as a function of the change of the dielectric constant of the solvent. Our model provides a tool for understanding how to manipulate chemical structures and their interaction with light at the molecular scale as plasmon-driven molecular jackhammers for applications at the interface with biological structures.

Transformation behavior and toxicity assessment of beaytlmethodeyammonNium chbride (BAC-12) disinfectant during hospital wastewater treatment.

This work focused on the transformation behavior of the emerging beaytlmethodeyammonium chbride (BAC-12) disinfectant existed in the treatment of medical sewage during its disinfection treatment. The degradation ability of ozone (O3) to BAC-12 was the best, followed by UV/NaOCl, UV, and NaOCl. The enhancement of BAC-12 in UV/NaOCl system is caused by the combined effect of UV photolysis, reactive chlorine species (RCS), and •OH. The transformation products of BAC-12 in the disinfection treatment were detected, and the chemical structure of products was rationalized by frontier molecular orbital and transition state theory methodologies. According to the ecological structure-activity relationship (ECOSAR) assessment, the intermediates of BAC-12 in UV, NaOCl, and UV/NaOCl treatments had lower half lethal concentration (LC50) and chronic toxicity (ChV) values with a higher ecotoxicity than BAC-12. O3 disinfection treatment of these toxic intermediates can significantly reduce the toxicity of the BAC-12 solution. This work provides necessary information on the potential environmental risks of BAC-12 arising from different disinfection methods in the treatment of medical wastewater.

Analyzing first-semester chemistry students’ transactive talk and problem-solving activities in an intervention study through a quantitative coding manual

IntroductionDuring the COVID-19 pandemic, digital video conferencing formats temporarily became the new norm at universities. Due to social distancing, these environments were often the only way for students to work together. In the present study, we investigated how first-semester chemistry students dealt with new, challenging content, i.e., quantum theories of chemical bonding such as molecular orbital (MO) theory, in such an unfamiliar collaboration environment. Studies in the field of Computer-Supported Collaborative Learning (CSCL) suggest that small groups working on complex tasks are particularly effective when students actively build on the ideas and reasoning of their peers, i.e., when they engage in transactive talk and when they structure their work on a metacognitive level by following typical problem-solving patterns.MethodsTo operationalize these constructs, we developed a coding manual through quantitative content analysis, that we used to analyze a total of N = 77 students working together in 21 small groups on two consecutive tasks: the creation of glossaries and the construction of concept maps on MO theory. Our manual showed very good characteristics in terms of internal consistency and inter-coder reliability. Based on the data obtained, it was possible to not only describe the student’s transactive communication and problem-solving activities, but to correlate it with other variables such as knowledge development in MO theory, which allowed us to compare the two different collaborative phases as well as different treatment groups.Results and discussionStudents showed a higher proportion of transactivity and problem-solving activities when constructing the concept maps than when creating glossaries. In terms of knowledge gains, a multiple linear regression analysis revealed that students in groups that derived consequences from their collaborative work showed greater improvements than students who did not, although the students’ prior knowledge remained the most influential factor. As for the different treatments, our data did not reveal any noticeable difference when students from a small group worked with either complementary or identical material before collaboration, neither in terms of transactive talk nor problem-solving patterns. All in all, we were able to develop and test a powerful tool to quantify transactive communication and problem-solving activities in a collaborative context.

Representing The World Around Us: Applications of Group Representation Theory to Molecular Orbital (MO) Theory

Molecular orbital (MO) theory is a theory at the forefront of modern chemistry, allowing for accurate descriptions of reactivity of molecules by using quantum mechanics to predict the location of electrons within a molecule, and their corresponding energies. The equations which govern their behavior, the Schrodinger equation, are often difficult to solve. Often, we can only approximate a solution using numerical methods. This paper discusses a method which exploits a molecule’s internal symmetry. Specifically, we use Group representation theory to help analyze and break down the molecular symmetry, and then use the analysis to help us find the MO’s. First, we establish key results about irreducible representations and characters. We then establish a correspondence between MO’s and irreducible representations. We then use the results we obtained to perform MO calculations on water (H2O). We then compare the results obtained via our MO theory calculations and Valance Bond Theory (VBT). We conclude by showing these calculations are best used for rough work, being most useful for deciding which atomic orbitals they arose from, and each MO’s energies relative to each other.

Bioassay-guided separation of antioxidants in Blaps rynchopetera Fairmaire and their theoretical mechanism

Blaps rynchopetera Fairmaire is a medicinal insect with a wide range of biological activities. Some of its activities, including anti-cancer and anti-inflammatory activities, are closely related to antioxidant capacity. In this study, a method was established to investigate components and theoretical mechanism of antioxidant from B. rynchopetera. As a result, two antioxidants were obtained by bioassay-guided separation and identified as 4-(2-hydroxyethyl)-1,2-benzenediol and 4-ethylbenzol-1,3-diol. Their EC50 were 20.20 ± 0.30 μM and 22.90 ± 1.30 μM for ABTS·+ scavenging, and 153.00 ± 2.00 μM and 301.00 ± 3.00 μM for DPPH· scavenging, respectively. The thermodynamic investigation indicated that the 2-OH of 4-(2-hydroxyethyl)-1,2-benzenediol and the 1-OH of 4-ethylbenzol-1,3-diol were more susceptible to be attacked by free radicals. They tended to exert antioxidant effects via the sequential proton loss electron transfer mechanism in polar media, whereas the hydrogen atom transfer mechanism was more likely to occur in non-polar media. In addition, frontier molecular orbital theory and energy barrier analysis suggested that 4-(2-hydroxyethyl)-1,2-benzenediol was more likely to react with DPPH·. These results confirmed that 4-(2-hydroxyethyl)-1,2-benzenediol had better antioxidant potential.

Ultra-high rate and long cycle life sodium-based dual-ion batteries enabled by Li2TiO3-modified cathode-electrolyte-interphase

Sodium-based dual-ion batteries (SDIBs) have received widespread attention due to their high voltage, low cost, safety, and eco-friendliness. Nevertheless, the irregular spherical graphite cathodes are limited by the mass transfer non-uniformity and sluggish reaction kinetics due to uneven anion migration through the highly tortuous pathways and the inductive anisotropic electric fields. Herein, we report a facile dissolution-precipitation-carbonation optimized modification strategy to synthesize a series of nano-Li2TiO3/C-modified graphite flake (GF-LTx, x = 1, 2.5, and 5) as cathode for SDIBs. The Li2TiO3-C-Cathode Electrolyte Interphase (Li2TiO3-C-CEI) trinity layer by in situ reactions shows good cycling performance. The intrinsic mechanism of Li2TiO3-C-CEI was further explored by DFT molecular orbital theory and distribution relaxation time (DRT) analysis. Notably, the GF-LT2.5 achieves 10,000 stable cycles at 3–5.2 V (vs. Na/Na+) with a initial capacity of 91.1 mAh g−1 and a decay rate of only 0.00217 % per cycle. Furthermore, GF-LT2.5 demonstrates an ultra-high rate performance of 100C with only 30 s for a single charge and 86 % capacity for low current density. Infrared thermography confirms the good thermal stability and safety of the gel-based flexible pouch cells. This work provides new insights into the design of high-rate performance, long-cycle stability, and high-safety energy storage systems.

Influence of hydrogen bond donor compound type on the properties of betaine based deep eutectic solvents: A computational and experimental approach

Novel deep eutectic solvents (DESs) based on Betaine as a hydrogen bond acceptor and Urea, Lactic acid, Glycerol, 1.2 - Propanediol, Xylitol as a hydrogen bond donor were prepared. Using computational approach, a theoretical analysis of compounds reactivity for hydrogen bond formation was carried out to justify the intermolecular interactions reactivity for hydrogen bond formation among the components. Through frontier molecular orbital theory and HOMO−LUMO values and various quantum chemical parameters, viz., ionization potential, electron affinities, electro negativity, chemical potential, global softness and hardness, electrophilicity and nucleophilicity indexes were calculated for all DESs. The calculated parameter namely charge transfer (ΔN) was used to evaluate the effectiveness of the formation of the DES. The value of charge transfer varies in the range 0.053–0.2836 eV and is higher for systems Betaine – Glycerol and Betaine – 1,2 - Propanediol. Electronegativity of the HBD varies in 4.2465< χ >7.2179 eV. They are promising options for applications that need to contact with water because of their hydrophilic nature. The formation of hydrogen bonds during the formation of DES was confirmed using the nuclear magnetic resonance (NMR) method. Donors of hydrogen bonds are able to ensure the formation of DES with Betaine, but the choice of the donor depends on the specific conditions of use and requirements for the solvent. Thermal behavior, surface tension, viscosity, electrical conductivity, рН of the prepared DES was investigated. Systems of the Betaine based DES with Xylitol and Urea have higher thermal stability (> 150 ºC). The highest values of surface tension are observed for DESs with Glycerol (65.02⋅103 J/m2) and 1.2-Propanediol (54.29⋅103 J/m2). The Betaine-Urea deep eutectic solvents (DES-1) and Betaine-Lactic acid (DES-2) systems have fairly high electrical conductivity (0.0091 and 0.4160 Sm/m). The effect of water on the properties (electrical conductivity, рН and surface tension) of DESs was investigated. The surface tension measurements revealed a broad range of surface tension, with water content being a major factor. This work has the effect of supplying new theoretical approach for a more deliberate comprehension on design of betaine-based DES as novel solvents for use in applications.

Transition Metals Doped into g-C3N4 via N,O Coordination as Efficient Electrocatalysts for the Carbon Dioxide Reduction Reaction.

The electrochemical carbon dioxide reduction reaction (CO2RR) is a potential and efficient method that can directly convert CO2 into high-value-added chemicals under mild conditions. Owing to the exceptionally high activation barriers of CO2, catalysts play a pivotal role in CO2RR. In this study, the transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is doped into g-C3N4 with a unique N,O-coordination environment, namely, TM-N1O2/g-C3N4. Herein, the catalytic performance and reaction mechanism for the CO2RR on TM-N1O2/g-C3N4 are systematically investigated by density functional theory methods. Especially, through the calculation of ΔG*H and ΔG*COOH/ΔG*OCHO, the catalysts with preference for the CO2RR over the hydrogen evolution reaction (HER) are selected for further study. Furthermore, Gibbs free energy computation results of each elementary step for the CO2RR on these catalysts indicate that Ti-N1O2/g-C3N4 has significant catalytic activity and selectivity for reducing CO2 to methanol (CH3OH) with the limiting potential (UL) of -0.55 V. Finally, through frontier molecular orbital theory and charge transfer analyses, the introduction of the O atoms illustrates that it is instrumental in regulating the electron distribution of the catalytic active site, thereby improving the catalytic performance. This work provides insight into the design of single-atom catalysts with unique coordination structures for the CO2RR.

Going Beyond Woodward and Hoffmann's Electrocyclizations and Cycloadditions: Sigmatropic Rearrangements.

On June 1, 1965, R. B. Woodward and Roald Hoffmann published their third communication in the Journal of the American Chemical Society in which they applied orbital symmetry control to explain the mechanism of a wide variety of valence isomerizations that they termed "sigmatropic reactions." This publication reveals the research trajectory taken by Hoffmann from which this portion of the no-mechanism problem was solved. Hoffmann used five different quantum chemical tools, all based on either extended Hückel theoretical calculations or frontier molecular orbital theory, in his research. Hoffmann's laboratory notebooks and his three draft manuscripts along with Woodward's four subsequent drafts have survived the past 59 years and provide an excellent window into the thinking and manuscript-writing processes used by these Nobel laureates in February-April 1965.

Efficient degradation of DDBAC in water by a heterogeneous Vis/H2O2 catalytic system based on MIL-53(Fe)

In this study, the iron-based metal–organic framework MIL-53(Fe) was successfully prepared by a solvent method and used as a photocatalyst for the efficient degradation of DDBAC under visible light. The morphology, structure and photocatalytic properties of MIL-53(Fe) were investigated by SEM, XRD, XPS and UV–vis DRS characterization methods. The optimum conditions for the degradation of DD pathways of DDBAC were analyzed in combination with DFT calculations. Based on molecular orbital theory and free radical quenching experiments, it was demonstrated that hydroxyl radicals were the main contributors in the oxidative degradation of DDBAC. The toxicity of DDBAC and its intermediates was evaluated by culturing Chlorella vulgaris, and the results showed that the Vis/MIL-53(Fe)/H2O2 system was capable of solution detoxification.

Theoretical Investigation of Rhodium-Decorated Gallium Nitride Nanotubes for Sulfur Hexafluoride Decomposition Products Sensing and Scavenging Applications.

Gas-insulated switchgear (GIS) plays an important role as a modern power distribution device in power plants and power stations, which is commonly filled with SF6 insulating gas. During the equipment operation, the inevitable partial discharge causes SF6 to be broken down into gas (SF4, SOF2, SO2, and H2S), which degrades the insulation performance of the GIS. This paper is devoted to the detection of partial discharge and the removal of SF4 and SOF2, which are not conducive to insulation, by exploring new gas-sensing materials for characteristic gas detection. Based on first-principles calculation, on the one hand, the most stable adsorption configurations of rhodium-decorated gallium nitride nanotubes (Rh-GaNNTs) and gas adsorption systems were obtained. On the other hand, the doping and adsorption mechanisms were analyzed by band structure, density of states, deformation charge density, and molecular orbital theory. Subsequently, the gas-sensitive performance of Rh-GaNNTs for these four impurity gases was evaluated by analyzing the sensing response and recovery time. The adsorption stability and recovery time of Rh-GaNNTs to these gases are ranked as SF4 > SOF2 > SO2 > H2S; the order of influence of gas adsorption on sensitivity response is H2S > SO2 > SF4 ≈ SOF2. Calculation results show the potential of Rh-doped surfaces as reusable H2S and SO2 sensors and suggest their use as gas scavengers to remove SF4 and SOF2, especially SOF2.

Synthesis, crystal structure, hirshfeld surface analysis, and computational studies of dimeric and polymeric cadmium complexes

In the current investigation, a new dimeric [Cd(DNBA)2(py)2]2 and a polymeric [Cd(DNBA)2(pyz)2]n cadmium complexes have been prepared by the reaction of 3,5-dinitrobenzoic acid (main ligand), nitrogen donor auxiliary ligands (pyridine and pyrazine), and Cd(II) sulphate in aqueous media. The crystal structures of the synthesized compounds were determined by single-crystal X-ray diffraction analysis. The crystal structures were investigated in terms of the coordination geometry, dihedral angles between various rings, and intermolecular interactions. The solid-state assembly was stabilized by various interatomic contacts, explored by Hirshfeld surface analysis. Void analysis was performed to predict the response of crystals to the applied stress. The optimized molecular geometries of the compounds were achieved utilizing the DFT approach along with the B3LYP functional/6–311G(d,p)/LANL2DZ basic set. MEP maps, molecular orbital theory, and quantum chemical parameters for the synthesized compounds were generated using the same level of theory.

Comparison of gas-sensitive properties of Pb, Pd and Pt metal-doped Ti3C2X2 for aqueous zinc ion battery H2 gas

This work aims to provide early warning of uncontrolled reactions in aqueous zinc-ion batteries by timely and effectively detecting H2 gas. The large specific surface area and rich pore structure of Ti3C2X2 (X = F, O, and OH) make it a good gas-sensitive sensing material, and the gas-sensitive properties of the material can be improved by metal doping. Therefore, in this paper, the gas-sensitive response properties of Pb, Pd and Pt metal-doped Ti3C2X2 (M-Ti3C2X2) to H2 are compared based on density functional theory (DFT) calculations. The adsorption mechanism was analyzed by structure optimization, density of states, frontier molecular orbital theory and differential charge density, and the results were in high agreement. Doping of three metals, Pb, Pd and Pt, improved the adsorption capacity of Ti3C2X2 for H2 gas to different degrees. The simulation results show that the energy gap of Pb-Ti3C2(OH)2 adsorbed gas changes most obviously, and the maximum change value of energy gap (Eg) is 297.56 %. And Pt-Ti3C2F2 and Pt-Ti3C2O2 adsorbed H2 with large adsorption energies and large charge transfers indicating that they can be used as H2 removers. The energy gaps after the adsorption of H2 by M-Ti3C2O2 are 0.109 eV, 0.163 eV, and 0.082 eV, and the change of Eg is 24.77 %, 16.56 %, and 67.07 %, respectively. The change of Eg for the adsorption of H2 by Pt-Ti3C2O2 adsorbed H2 with a resistivity change of 67.07 %. This is caused by the irreversibility of adsorption due to too strong adsorption resulting in elongation of Pt-O bond length after adsorption. For the detection of H2, the properties of several doped materials were ranked as follows: Pb-Ti3C2(OH)2 > Pt-Ti3C2O2 > Pb-Ti3C2F2 > Pb-Ti3C2O2 > Pd-Ti3C2O2 > Pd-Ti3C2(OH)2 > Pt-Ti3C2F2 > Pt-Ti3C2(OH)2 > Pd-Ti3C2F2. In summary, it is shown that Ti3C2X2 doped with Pb, Pd and Pt metals is a potential H2 gas-sensitive material that can be a new material for online monitoring of fault gas content in aqueous zinc-metal energy storage batteries.

Preferred Electric Field Mechanism for Frustrated Lewis Pair Reactivity.

This study employs computational methods to investigate the mechanism of H2 activation by frustrated Lewis pair (FLP) species, including both intermolecular and intramolecular nitrothane/borane FLP systems. Previous studies have proposed two qualitative reactivity mechanism models to explain the facile cleavage of H2 by FLPs. The findings of this study support the electric field mechanism as the favorable pathway for H2 cleavage. Utilizing frontier molecular orbital theory and energy decomposition analysis, the study explores the electronic structure and nature of the reactions under an external electric field (EEF). Analysis using the activation strain model highlights the significant influence of geometrical deformation energies of FLPs on the activation barriers of H2 activation reactions. Computational results suggest that H2 activation by FLP molecules follows the electric field mechanism, indicating the potential of the FLP/EEF combination as an effective activator for inert molecules.

Adsorption behavior of temozolomide, carmustine, procarbazine, and lomustine anticancer drugs on zinc oxide nanocage: A DFT study

The adsorption behavior of zinc oxide (Zn12O12) nanocage toward delivering the temozolomide (TMZ), carmustine (CM), procarbazine (PR), and lomustine (LO) anticancer drugs was herein investigated utilizing the density functional theory (DFT) method. The emerging outcomes unveiled the potential efficiency of the Zn12O12 nanocage toward adsorbing the TMZ, CM, PR, and LO drugs and showed prominent negative values of binding energies (ΔEbind) up to −14.69 kcal.mol−1. Among the studied complexes, the Zn12O12-TMZ complex showed the most preferential ΔEbind values in the gas and water phases compared to other studied complexes with values up to −14.69 and −12.88 kcal.mol−1, respectively. The quantum theory of atoms in molecules announced the occurrence of the adsorption process between the Zn12O12 nanocage and anticancer drugs via polar covalent interactions and electrostatic interactions. Based on frontier molecular orbital theory affirmations, the electronic parameters of Zn12O12 nanocage changed preferentially upon adsorption of the studied drug within the most stable configurations. Moreover, the Zn12O12-drug complexes exhibited short recovery times for drug desorption from the nanocage. The results clearly confirmed that the Zn12O12 nanocage is an ideal candidate for the highly efficient development of anticancer TMZ, CM, PR, and LO drug carriers.

Configuration Interaction in Frontier Molecular Orbital Basis for Screening the Spin-Correlated, Spatially Separated Triplet Pair State 1(T···T) Formation.

In the theoretical screening of Singlet Fission rates in molecular aggregates, often the frontier molecular orbital model for dimers is employed. However, the dimer approach fails to account for recent experimental findings that suggest singlet fission progresses through a further intermediate state featuring two spatially separated, spin-correlated triplets, specifically a 1(T···T) state. We address this limitation by generalizing the often used frontier molecular orbital model for singlet fission by incorporation of both separated Charge Transfer (C···T) and 1(T···T) states as well as mixed triplet-charge transfer states, delivering analytic expressions for the diabatic matrix elements. Applying the methodology to the perylene diimide trimer, we examine the packing dependence of competing formation pathways of the 1(T···T) state by evaluation of diabatic matrix elements.

Effect of pre-oxidation and cooling process on characteristics and mechanism of the coal re-ignition

Based on the engineering background that the sealed fire area is easy to reignite, the reignition characteristics of pre-oxidized coals (POC) after cooling are studied. Predecessors mainly explain this problem from the perspective of pre-oxidation affecting coals pore structure. This paper analyzes the effects of different pre-oxidation temperatures and cooling atmospheres on coal physical and chemical structure. The changes of coals during oxidation-cooling-reoxidation were studied by means of a programmed heating device, low temperature nitrogen adsorption experiment, FTIR and quantum chemical calculation. The results show that the average pore size of the coal cooled in nitrogen at the same pre-oxidation temperature is smaller than that of the coal cooled in dry air, while the spontaneous combustion characteristics of the coal cooled in nitrogen are stronger than those of raw coal, and spontaneous combustion characteristics of coal cooled in air are the opposite. The oxygen-containing functional groups of the coal cooled in nitrogen are pyrolyzed to produce active sites which can exist stably in nitrogen. Then, the rationality of “The active sites tend to be alkyl radical” is analyzed and speculated by molecular orbital theory, and it's found that alkyl radicals can release lots of heat at 30 °C.

Construction frontier molecular orbital prediction model with transfer learning for organic materials

The frontier molecular orbitals of organic semiconductor materials play a crucial role in the performance of photoelectric devices, including organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), and organic photodetectors (OPDs). In this work, a model for predicting frontier molecular orbital of organic materials, including HOMO and LUMO levels, is established with the extreme gradient boosting algorithm and Klekota-Roth fingerprints. The correlation coefficients of HOMO or LUMO energy levels in the testing set are 0.75 and 0.84 in the transfer model from 11,626 DFT data in Harvard Energy database to 1198 experimental data in literature. The difference between the ML predicted value and the experimental value is smaller than the difference between ML prediction and DFT calculation, always less than 10%. Moreover, based on correlation and SHAP interpretability analysis, 13 key structural fragments influencing energy levels are selected to further verify the effective regulation of the frontier molecular orbital by the key structural fragments in practical applications. Considering the completely opposite regulatory functions of key structural fragments on HOMO and LUMO energy levels, four new Y6 derivatives, Y-PCP, Y-P6F, Y-PCF, and Y-P4FC, are designed to flexibly modify the HOMO and LUMO energy levels. The prediction trends of ML align closely with the computational trends from DFT. It is worth noting that the accuracy of LUMO energy level prediction by the prediction model makes up for the instability of DFT calculation on LUMO energy level. This work offers a cost-effective method to accelerate the acquisition of electronic properties of organic materials.