Highest Occupied Molecular Orbital-lowest Unoccupied Molecular Orbital Research Articles

Screening Carbon-Boron Frustrated Lewis Pairs for Small-Molecule Activation including N2 , O2 , CO, CO2 , CS2 , H2 O and CH4 : A Computational Study.

Dinitrogen (N2 ) activation is particularly challenging under ambient conditions because of its large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (10.8 eV) and high bond dissociation energy (945 kJ mol-1 ) of the N≡N triple bond, attracting considerable attention from both experimental and theoretical chemists. However, most effort has focused on metallic systems. In contrast, nitrogen activation by frustrated Lewis pairs (FLPs) has been initiated recently via theoretical calculations. Here we perform density functional theory (DFT) calculations to screen a series of experimentally viable FLPs for small-molecule activation including N2 , O2 , CO, CO2 , CS2 , H2 O and CH4 . In addition, aromaticity is found to play an important role in most of these small-molecule activation. The particularly thermodynamic stabilities of the activation products and low reaction barriers could be a step forward for the development of FLP towards small-molecule activation including N2 , inviting experimental chemists' verification.

Structural predictions of three medium-sized thiolate-protected gold nanoclusters Au44(SR)30, Au56(SR)32, and Au60(SR)34.

The knowledge of structural evolution among thiolate-protected gold nanoclusters is not only helpful for understanding their structure-property relationship but also provides scientific evidence to rule-guided structure predictions of gold nanoclusters. In this paper, three new atomic structures of medium-sized thiolate-protected gold nanoclusters, i.e. Au44(SR)30, Au56(SR)32, and Au60(SR)34, are predicted based on the grand unified model and ring model. Two structural evolution rules, i.e., Au44(SR)28 + [Au12(SR)4] → Au56(SR)32 + [Au12(SR)4] → Au68(SR)36 and Au44(SR)30 + [Au8(SR)2] → Au52(SR)32 + [Au8(SR)2] → Au60(SR)34 + [Au8(SR)2] → Au68(SR)36, are explored. The generic growth patterns underlying both sequences of nanoclusters can be viewed as sequential addition of four and three highly stable tetrahedral Au4 units on the cores, respectively. In addition, density functional theory calculations show that these three newly predicted gold nanoclusters have very close formation energies with their adjacent structures, large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, and all-positive harmonic vibration frequencies, indicating their high stabilities.

Adsorption of cytosine on Si and Ge doped graphene: A DFT study

This study describes how the cytosine adsorption on Si and Ge-doped Graphene uses density functional theory (DFT) calculations. The adsorption energies of cytosine on Si and Ge-doped Graphene are computed. The method used a hybrid B3LYP approach with 6-31G (d,p) and LANL2DZ basis sets to determine the Highest Occupied Molecular Orbital -Lowest Unoccupied Molecular Orbital HOMO and LUMO states and descriptors; and charge distribution potential. According to charge distributions, both Ge-doped and Si-doped graphene structures are sensitive to the cytosine base. The DNA base cytosine plays a crucial role as an adsorbent. When cytosine was adsorbed on Ge- and Si-doped graphene structures, the Highest Occupied Molecular Orbital -Lowest Unoccupied Molecular Orbital (HOMO-LUMO) gap decreased. This finding implies that the electrical conductivity of both systems has increased. The result shows that the Ge- and Si-doped graphene structures might be introduced as strong adsorbents for biosensor applications in various fields.

2-(3-Methyl-4,5-Dihydro-1H-1,2,4-Triazol-5-One-4-yl-Azomethine)-Phenyl Cinnamate: Theoretical and Experimentical Properties

In this study, theoretically spectral values of 2-(3-methyl-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl-azomethine)-phenyl cinnamate was calculated according to Gaussian G09W software. These theoretical values were compared with experimental values and obtained the results are interpreted. For this purpose, firstly, 2-(3-methyl-4,5-dihydro-1H-1,2,4-triazol-5-one-4-yl-azomethine)-phenyl cinnamate molecula were optimized using B3LYP/6-311G(2d,p) basis set. Bond angles, bond lengths, dihedral angles, dipole moments, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy, mulliken charges and total energy of the molecule were calculated with B3LYP/6-311G(2d,p) basis set. UV-vis values in ethanol were calculated. In addition, Theoretically calculated IR values of this compound were calculated in gas phase. The calculated IR values are multiplied with appropriate scale factors and the values obtained according to B3LYP method is obtained using theoretical infrared spectrum. The identification of calculated IR values were used veda4f program. Finally, 1H-NMR and 13C-NMR spectral values according to GIAO method was calculated in gas phase and in DMSO solvent. Theoretically and experimentally values were inserted into the graphic according to equitation of δexp=a+b. δ calc. The standard error values were found via SigmaPlot program with regression coefficient of a and b constants. The calculated and experimental results were exhibited a very good agreement.

Effects of Atypical Hydrogen Bonds and π-π Interactions on Nonlinear Optical Properties: Dimers of Triangular Structures Based on Perylene, Naphthalene, and Pyromellitic Diimides.

Nonlinear optical (NLO) materials have become important materials in the field of high-speed optical devices due to the changes in light absorption and refraction caused by the photoelectric field. Compounds tend to exist as aggregates rather than single molecules, so intermolecular interactions are crucial to the nature of aggregates. Therefore, to study the effects of intermolecular interactions on nonlinear optical properties, we use a dimer simplified model and adopt the methods of controlling variables, which are the different intermolecular interactions resulting from the different stacking patterns of dimers based on the same monomer structures (2PMDI-1NDI and 2NDI-1PDI). It is found that compared with dimers involving π-π interactions, dimers involving C-H···O interactions have shorter intermolecular distances, larger intermolecular interaction energies, and smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps. Moreover, the C-H···O interactions are more conducive to the intermolecular charge transfers and more beneficial for increasing the nonlinear optical response values of aggregates with respect to π-π interactions. This work provides an important basis for the influence of intermolecular interactions on nonlinear optical properties.

Curious Case of Singlet Triplet Gaps in Nonlinear Polyaromatic Hydrocarbons

The singlet triplet (ST) gap of linear polyacenes decays exponentially with the system size as a result of extended conjugation and reducing highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps. These low ST gaps can ideally be leveraged toward energy applications but are hindered by the decreasing stability of the systems. Thus, there is the need to understand the ST gap of nonlinear polyacenes, which are markedly more stable than their linear counterparts. Here, we show that the ST gaps of the nonlinear polyacenes do not decrease with the system size and have no correlation with the HOMO-LUMO gaps or increased conjugation. The reason behind this is identified as the high multireference character of the triplet high-spin state. These unprecedented results are in stark contrast to the observations in linear polyacenes and are due to the combined effects of topology and geometrical factors.

High photometric and spectroscopic features of emerald light emitter terbium (III) [formula omitted]-Ketoester functionalised complexes for modern lighting devices

Emerald light-emitting terbium complexes contribute to the progress of advance lighting devices, a sequence of five complexes is synthesized via mixing of terbium ion, 2-(methacryloxy) ethylacetatoacetate (MAE), and neutral auxiliary ligands (batho, dmbipy, phen and bipy) and characterize with different spectroscopic techniques. The thermal stability of complexes is investigated by thermogravimetric and derivative thermogravimetric (TG-DTG) curves. Highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap resembles experimentally observed bandgap values. The emission spectra, color coordinates, color purity, and correlated color temperature (CCT) investigate the color and nature of specific light. The emission profile of terbium complexes shows four peaks at 494, 547, 587, and 622 nm attributed 5D4 → 7FJ, (J = 6, 5, 4, 3) transitions. Out of them, one is dominant, located at 547 nm which is responsible for emerald emissions. Further, the CIE map approve that color coordinates fall in a green area of map and color purity defines the saturation in color from T1 to T5 complexes. The nature of emerald light is cool, concluded on the base of results of CCT that are found in between 7904 and 8511 K. All superlative results of synthesized samples inspire their excellent practicability in advanced photonic appliances.

Magic Numbers in Octahedral Ligated Metal-Chalcogenide Superatoms.

The attainment of the superatomic state offers a unifying framework for the periodic classification of atomic clusters. Metallic clusters attain the superatomic state via the confined nearly free electron gas model that leads to groupings of quantum states marked by radial and angular momentum quantum numbers. We examine ligated octahedral metal-chalcogenide clusters where the nearly free electron gas model is invalid; however, the high symmetry can also lead to the bunching of electronic states. For octahedral TM6E8L6 clusters (TM = transition metal; E = chalcogen; L = ligand), the electronic shells are filled for valence electron counts of 96, 100, and 114 electrons. These magic electron counts are marked by large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, high ionization energies, and low electron affinity─all classic signatures of the superatomic state. We also find that clusters with electron counts differing from the magic counts show periodic patterns reminiscent of those observed in the periodic table of elements.

Ultrasonic Clusterization Process to Prepare [(NNCO)6Co4Cl2] as a Novel Double-Open-Co4O6 Cubane Cluster: SXRD Interactions, DFT, Physicochemical, Thermal Behaviors, and Biomimicking of Catecholase Activity.

A novel double-open-cubane (NNCO)6Co4Cl2 cluster with a Co4O6 core was made available under aqua-ultrasonic open atmosphere conditions for the first time. The ultrasonic clusterization of the (3,5-dimethyl-1H-pyrazol-1-yl)methanol (NNCOH) ligand with CoCl2·6H2O salts in ethanol yielded a high-purity and high-yield cluster product. Energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR), and ultraviolet (UV)–visible techniques were used to elucidate the clusterization process. The double-open-Co4O6 cubane structure of the (NNCO)6Co4Cl2 cluster was solved by synchrotron single-crystal X-ray diffraction (SXRD) and supported by density functional theory (DFT) optimization and thermogravimetric/differential TG (TG/DTG) measurements; moreover, the DFT structural parameters correlated with the ones determined by SXRD. Molecular electrostatic potential (MEP), Mulliken atomic charge/natural population analysis (MAC/NPA), highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO), density of states (DOS), and GRD quantum analyses were computed at the DFT/B3LYP/6-311G(d,p) theory level. The thermal behavior of the cluster was characterized to support the formation of the Co4O6 core as a stable final product. The catalytic property of the (NNCO)6Co4Cl2 cluster was predestined for the oxidation process of 3,5-DTBC diol (3,5-di-tert-butylbenzene-1,2-diol) to 3,5-DTBQ dione (3,5-di-tert-butylcyclohexa-3,5-diene-1,2-dione).

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Phosphonium-Based Ionic Thermally Activated Delayed Fluorescence Emitters for High-Performance Partially Solution-Processed Organic Light-Emitting Diodes

Molecular dynamics, transport property, and surface stoichiometry of plasma polymerized cyclohexane thin films

The properties of cyclohexane (CHex) and plasma polymerized cyclohexane (PPCHex) thin films are studied, and the results are compared with those obtained using a computing model (under the density functional theory framework). Quantum chemical calculations are performed to calculate their molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gaps, thermodynamic stability, chemical reactivity, and vibrational properties. The HOMO–LUMO energy gap sharply decreased in the case of the PPCHex thin film compared to that of CHex. Gibbs free energy shows a similar phenomenon where the enthalpy of PPCHex (formation) is almost six times higher than that of CHex. The computed FTIR spectra indicate good agreement with the experimental results. RMS roughness shows a smooth surface, and it is compared with the FESEM image. Moreover, the dielectric constant and electrical conductivity of the PPCHex thin films are also studied.

Density Functional Theoretical Computational Studies on 3-Methyl 2-Vinyl Pyridinium Phosphate

The molecular structure of 3-methyl 2-vinyl pyridinium phosphate (3M2VPP) has been optimized by using Density Functional Theory using B3LYP hybrid functional with 6-311++G (d, p) basis set in order to find the whole characteristics of the molecular complex. The theoretical structural parameters such as bond length, bond angle, and dihedral angle are determined by DFT methods and are well agreed with the single crystal X-ray diffraction parameters. Theoretical vibrational, highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO), natural bonding orbital (NBO), and electrostatic potential (ESP) analyses have also been performed. Based on the potential energy distribution (PED), the complete vibrational assignments, analysis, and correlation of the compound’s fundamental modes have been determined. Natural bonding orbital (NBO) analysis is used to evaluate the intramolecular charge transfer and hyper-conjugative interaction of the molecule. B3LYP/6-311++G (d, p) basis set determines the electronic properties such as HOMO–LUMO energies and is used to understand the kinetic stability and chemical reactivity of the studied compound. Molecular electrostatic potential (MEP) is used to investigate the electron density distribution and chemical reactive sites of 3M2VPP. The dipole moment, total polarizability, and the first-order hyperpolarizability calculations have been carried out for the studied molecule. Hirshfeld surface analysis has been done to study the intermolecular interactions in the studied complex.

Multi spectroscopic and computational investigations on the electronic structure of oxyclozanide

The present work contributes to a combined theoretical and experimental investigation on oxyclozanide. The experimental vibrational spectra were characterized by Fourier transform infrared (4000-400 cm−1), Fourier transform Raman (4000-400 cm−1), 1H and 13C NMR were recorded in Deuterated methanol, UV–Vis (200–400 nm) techniques and theoretical optimized molecular geometry, harmonic vibrational spectra, magnetic spectra, and electronic spectra was calculated by Density Functional Theory (DFT) employed with B3LYP/6-311++G(d,p) basis set and compared with experimental data. The highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO) energy was also calculated for the titled compound. The intermolecular interactions have been addressed through Hirshfeld surface analysis. In addition, Natural bond orbital (NBO) analyses of the title compound were performed to evaluate the suitable reactivity site and chemical stabilization behavior, Mulliken atomic charge distribution, and molecular electrostatic potential energy surfaces, were calculated to get a better insight into the structure of oxyclozanide. The experimental and theoretical findings suggest an excellent correlation to confirm the structure of oxyclozanide.

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Influence of Alkali Metal Doping and BN Substitution on the Second-Order Nonlinear Optical Properties of Graphyne: A Theoretical Perspective.

The electronic and nonlinear optical (NLO) properties of BN-substituted graphynes and the corresponding alkali-doped hybrid systems have been determined using density functional theory. When the carbon atoms in the graphyne are replaced by BN pairs, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (Egap) increases to some extent, and the static first hyperpolarizabilities (β0) of the novel systems hardly increase. However, when an alkali atom is introduced on the surface of BN-substituted graphyne, the doping effect can effectively modulate the electronic and NLO properties. Doping the alkali atom can significantly narrow the wide Egap of BN-substituted graphynes in the range of 1.03-2.03 eV. Furthermore, the doping effect brings considerable β0 values to these alkali-doped systems, which are 52-3609 au for Li-doped systems and 3258-211 053 au for Na/K-doped ones. The result reveals that the β0 values of alkali-doped complexes are influenced by the atomic number of alkali metals and the proportion of BN pairs. The nature of the excellent NLO responses of alkali-doped complexes can be understood by the low excitation energy of the crucial excited state and the analysis of the first hyperpolarizability density. Besides, these alkali-doped complexes have a deep-ultraviolet working region. Therefore, the combined effect of alkali metal doping and BN substitution can be an excellent strategy to design novel high-performance NLO materials based on graphyne.

Excited States of Metal-Adsorbed Dimethyl Disulfide: A TDDFT Study with Cluster Model.

The optical near field refers to a localized light field near a surface that can induce photochemical phenomena such as dipole-forbidden transitions. Recently, the photodissociation of the S–S bond of dimethyl disulfide (DMDS) was investigated using a scanning tunneling microscope with far- and near-field light. This reaction is thought to be initiated by the lowest-energy highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition of the DMDS molecule under far-field light. In near-field light, photodissociation proceeds at lower photon energies than in far-field light. To gain insight into the underlying mechanism, we theoretically investigated the excited states of DMDS adsorbed on Cu and Ag surfaces modeled by a tetrahedral 20-atom cluster. The frontier orbitals of the molecule were delocalized by the interaction with the metal, resulting in narrowing of the HOMO–LUMO gap energy. The excited-state distribution was analyzed using the Mulliken population analysis, decomposing molecular orbitals into metal and DMDS fragments. The excited states of the intra-DMDS transitions were found over a wider energy range, but at low energies, their oscillator strengths were negligible, which is consistent with the experimental results. Sparse modeling analysis showed that typical electronic transitions differed between the higher and lower excited states. If these low-lying excited states are efficiently excited by near-field light with different selection rules, the S–S bond dissociation reaction can proceed.

Doping‐Mediated Energy‐Level Engineering of M@Au12 Superatoms (M=Pd, Pt, Rh, Ir) for Efficient Photoluminescence and Photocatalysis

AbstractWe synthesized a series of MAu12(dppe)5Cl2 (MAu12; M=Au, Pd, Pt, Rh, or Ir; dppe=1,2‐bis(diphenylphosphino)ethane), which have icosahedral M@Au12 superatomic cores, and systematically investigated their electronic structures, photoluminescence (PL) and photocatalytic properties. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was expanded when doping an M element positioned at the lower left of the periodic table. The PL quantum yield was enhanced with an increase in the HOMO–LUMO gap and reached 0.46–0.67 for MAu12 (M=Pt, Rh, or Ir) under deaerated conditions. The bright PLs from MAu12 (M=Pt, Rh, or Ir) were assigned to phosphorescence based on quenching by O2. MAu12 (M=Pt, Rh, or Ir) acted as a more efficient and stable photocatalyst than Au13 for intramolecular [2+2] cycloaddition of bisenone via the oxidative quenching cycle. This study provides rational guides for designing photoluminescent and photocatalytic gold superatoms by the doping of heterometal elements.

Silver Ion-Induced Formation of Unprecedented Thorium Nonamer Clusters via Lacuna-Construction Strategy

Silver Ion-Induced Formation of Unprecedented Thorium Nonamer Clusters via Lacuna-Construction Strategy

Binding Energy of Triplet Excitons in Nonfullerene Acceptors: The Effects of Fluorination and Chlorination.

One strategy to improve the photovoltaic properties of nonfullerene acceptors (NFAs), employed in state-of-art organic solar cells, is the rational fluorination or chlorination of these molecules. Although this modification improves important acceptor properties, little is known about the effects on the triplet states. Here, we combine the polarizable continuum model with an optimally tuned range-separated hybrid functional to investigate this issue. We find that fluorination or chlorination of NFAs decreases the degree of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) overlap along these molecules. Consequently, the energy gap between T1 and S1 states, ΔEST = ES1 - ET1, also decreases. This effect reduces the binding energy of triplet excitons, which favors their dissociation into free charges. Furthermore, the reduction of ΔEST can contribute to mitigating the losses produced by the nonradiative deactivation of the T1 excitons. Interestingly, although Cl has a lower electronegativity than F, chlorination is more effective to reduce ΔEST. Since the chlorination of NFAs is easier than fluorination, Cl substitution can be a useful approach to enhance solar energy harvesting using triplet excitons.

Predicting Dinitrogen Activation by Five-Electron Boron-Centered Radicals.

Due to the high bond dissociation energy (945 kJ mol-1) and the large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (10.8 eV), dinitrogen activation under mild conditions is extremely challenging. On the other hand, the conventional Haber-Bosch ammonia synthesis under harsh conditions consumes more than 1% of the world's annual energy supply. Thus, it is important and urgent to develop an alternative approach for dinitrogen activation under mild conditions. In comparison with transition metals, main group compounds are less explored for nitrogen activation. Here, we carry out density functional theory calculation to screen boron radicals for dinitrogen activation. As a result, the experimentally available seven-electron boron-centered radicals are found to be inactive to N2 activation, whereas some five-electron boron-centered radicals become favorable for dinitrogen activation, inviting experimental chemists' examination. The principal interacting spin-orbital analyses suggest that a five-electron boron-centered radical can mimic a transition metal on a synergic interaction with dinitrogen in the transition states.