Lowest Unoccupied Molecular Orbital Gap Research Articles

Tetrahexahedral binary transition metal compound sub-nanoclusters

We explore new transition metal (TM) compound sub-nanoclusters, TM8X6 (TM = Mn, Fe, Co and X = P, B, As), using density functional theory. Their optimized geometric structures show the same polyhedral structure (tetrahexahedron) independent of a kind of TM and metalloid (X), where eight TM atoms form a cubic structure capped with six metalloid (X) atoms. Incorporating an extra TM atom into the TM cubic results in an endohedral structure, TM9X6. Encapsulation of an additional TM atom merely changes the binding energy except for the Co boride cluster. The binding energy of Co8B6 increases by incorporating an additional Co atom, in which it is observed that the electron density is accumulated between B and all Co atoms (Co atoms both at the center and at the edges), but in other clusters, the electron excess is found mainly between TM atoms. The MnnP6 (n = 8 and 9) clusters have a high adiabatic electron affinity (>6 eV) due to the relatively large difference in electronegativity between Mn and P. The highest occupied molecular orbital and lowest unoccupied molecular orbital gaps of all clusters lie in the visible range. The interaction between nanoclusters and graphene with a single vacancy is studied as a function of the different cluster landing site on the graphene, where the geometric structure change of the clusters strongly depends on the adsorption site.

Hexadecanoic acid analogs as potential CviR-mediated quorum sensing inhibitors in Chromobacterium violaceum: an in silico study

Chromobacterium violaceum is a Gram-negative, rod-shaped and opportunistic human pathogen. C. violaceum is resistant to various antibiotics due to the production of quorum sensing (QS)-controlled virulence factor and biofilm formation. Hence, we need to find alternative strategies to overcome the antimicrobial resistance and biofilm formation in Gram-negative bacteria. QS is a mechanism in which bacteria’s ability to regulate the virulence factors and biofilm formations leads to disease progression. Previously, hexadecanoic acid was identified as a CviR-mediated quorum-sensing inhibitor. In this study, we aimed to discover potential analogs of hexadecanoic acid as a CviR-mediated quorum-sensing inhibitor against C. violaceum by using ADME/T prediction, density functional theory, molecular docking, molecular dynamics and free energy binding calculations. ADME/T properties predicted for analogs were acceptable for human oral absorption and feasibility. The highest occupied molecular orbitals and lowest unoccupied molecular orbitals gap energies predicted and found oleic acid with –0.3748 energies. Docosatrienoic acid exhibited the highest binding affinity −8.15 Kcal/mol and strong and stable interactions with the amino acid residues on the active site of the CviR protein. These compounds on MD simulations for 100 ns show strong hydrogen-bonding interactions with the protein and remain stable inside the active site. Our results suggest hexadecanoic acid analogs could serve as anti-QS and anti-biofilm molecules for treating C. violaceum infections. However, further validation and investigation of these inhibitors against CviR are needed to claim their candidacy for clinical trials. Communicated by Ramaswamy H. Sarma

A high-performance S-TENG based on the synergistic effect of keratin and calcium chloride for finger activity tracking

Triboelectric nanogenerator (TENG) is one of the key research directions for future human-computer interaction (HCI), biomedicine, and environmental protection. Bio-based materials are an essential branch of many degradable materials. Keratin has attracted much attention due to its advantages of easy access, biodegradability, and good biocompatibility. A highly sensitive single-electrode TENG (S-TENG) based on CaCl2/PVA/keratin and Ecoflex with micro-domes is designed. The excellent stability (18,000 cycles) and stretchability (200%) of the sensor are confirmed by research. Moreover, the presence of CaCl2 and keratin can significantly increase the S-TENG's output voltage, and the reason is also explored by the density functional theory (DFT) method. Through simulation, it is found that the decrease of the HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) gap and the increase of the electrostatic potential are the root causes of the voltage increase. Relying on the excellent characteristics of the S-TENG, finger curvatures, gestures, and object shapes are recognized. Among them, the accuracy of object shape recognition by machine learning algorithm reached 98.1%. This study provides a new method for improving the output efficiency and prolonging the service life of S-TENG and confirms the feasibility of the electron cloud trap model to explain biomass triboelectric materials by keratin and CaCl2.

Strategic Development of Dielectric Strength Prediction Protocol for Perfluorocarbon and Nonperfluorocarbon Compounds

Predicting the dielectric strengths of organic compounds is critical for identifying potential insulating gases. However, experimental evaluation techniques are time-consuming, and current computational protocols are limited in scope. In this study, to develop a reliable prediction protocol for the dielectric strengths of a broad array of perfluorocarbon (PFC) and non-PFC compounds, systematic linear regression is combined with computational calculations of relevant core factors. The designed equation-based protocol is demonstrated to have four core factors, including two high-correlation factors (polarizability and molecular weight) and two critical factors (ionization energy and highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap). The two critical factors are crucial for determining a suitable protocol, as reliable predictions of dielectric strength are only possible if the ionization energy and HOMO–LUMO gap are maintained within specified ranges for all the compounds. These findings can act as design guidelines for future computational protocols to predict the insulating properties of PFC and non-PFC compounds.

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.

Phenothiazine- isophorone dyes (D–π–A and A–π–D–π–A): synthesis, electronic properties and DFT computational study

PurposeThis paper aims to prepare a new donor–π–acceptor (D–π–A) and acceptor–π– D–π–A (A–π–D–π–A) phenothiazine (PTZ) in conjugation with vinyl isophorone (PTZ-1 and PTZ-2) were designed and their molecular shape, electrical structures and characteristics have been explored using the density functional theory (DFT). The results satisfactorily explain that the higher conjugative effect resulted in a smaller high occupied molecular orbital–lowest unoccupied molecular orbital gap (Eg). Both compounds show intramolecular charge transfer (ICT) transitions in the ultraviolet (UV)–visible range, with a bathochromic shift and higher absorption oscillator strength, as determined by DFT calculations.Design/methodology/approachThe produced PTZ-1 and PTZ-2 sensors were characterized using various spectroscopic methods, including Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (1H/13CNMR). UV–visible absorbance spectra of the generated D–π–A PTZ-1 and A–π–D–π–A PTZ-2 dyes were explored in different solvents of changeable polarities to illustrate positive solvatochromism correlated to intramolecular charge transfer.FindingsThe emission spectra of PTZ-1 and PTZ-2 showed strong solvent-dependent band intensity and wavelength. Stokes shifts were monitored to increase with the increase of the solvent polarity up to 4122 cm−1 for the most polar solvent. Linear energy-solvation relationship was applied to inspect solvent-dependent Stokes shifting. Quantum yield (ф) of PTZ-1 and PTZ-2 was also explored. The maximum UV–visible absorbance wavelengths were detected at 417 and 419 nm, whereas the fluorescence intensity was monitored at 586 and 588 nm.Originality/valueThe PTZ-1 and PTZ-2 dyes leading to colorimetric and emission spectral changes together with a color shift from yellow to red.

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

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

Ce(Ⅲ) activates peroxymonosulfate for the degradation of substituted PAHs

Substituted polycyclic aromatic hydrocarbons (SPAHs) are being intensively investigated, considering their high toxicity. Additionally, the mechanism of the effect of substituents on the removal of SPAHs and the activation of Ce(III) ions on peroxymonosulfate (PMS) have not been explored. Here we evaluated the removal efficiency of SPAHs in the oxidation system constructed by Ce(Ⅲ) ions and PMS, with emphasized the effect of substituents on SPAHs degradation. Ce(Ⅲ) has high catalytic performance for PMS, and the degradation percentage of all pollutants was higher than 92%. The significantly negative correlation between the reaction rate constants of SPAHs and the highest occupied molecular orbital-the lowest unoccupied molecular orbital gap, confirms that substituents lead to the differences in the degradation of SPAHs. The generation of reactive oxygen species (SO4•−, •OH, and 1O2) is based on the electron transfer between Ce(Ⅲ) and PMS, and the contribution of ROS to substituted naphthalene varies due to the role of substituents. The Ce(Ⅳ)/Ce(Ⅲ) cycle accelerates the activation of PMS. Based on the transformation products and condensed Fukui function, the possible degradation pathways are inferred. In addition, inorganic anions and organic matter have little effect on the Ce(Ⅲ)/PMS system, which is a prerequisite for applying this system to real-world waste-water for SPAHs removal. This work demonstrates a new model of the degradation mechanism of SPAHs in the Ce(Ⅲ)/PMS system.

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.

Halogen-Based 17β-HSD1 Inhibitors: Insights from DFT, Docking, and Molecular Dynamics Simulation Studies.

The high expression of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) mRNA has been found in breast cancer tissues and endometriosis. The current research focuses on preparing a range of organic molecules as 17β-HSD1 inhibitors. Among them, the derivatives of hydroxyphenyl naphthol steroidomimetics are reported as one of the potential groups of inhibitors for treating estrogen-dependent disorders. Looking at the recent trends in drug design, many halogen-based drugs have been approved by the FDA in the last few years. Here, we propose sixteen potential hydroxyphenyl naphthol steroidomimetics-based inhibitors through halogen substitution. Our Frontier Molecular Orbitals (FMO) analysis reveals that the halogen atom significantly lowers the Lowest Unoccupied Molecular Orbital (LUMO) level, and iodine shows an excellent capability to reduce the LUMO in particular. Tri-halogen substitution shows more chemical reactivity via a reduced HOMO–LUMO gap. Furthermore, the computed DFT descriptors highlight the structure–property relationship towards their binding ability to the 17β-HSD1 protein. We analyze the nature of different noncovalent interactions between these molecules and the 17β-HSD1 using molecular docking analysis. The halogen-derived molecules showed binding energy ranging from −10.26 to −11.94 kcal/mol. Furthermore, the molecular dynamics (MD) simulations show that the newly proposed compounds provide good stability with 17β-HSD1. The information obtained from this investigation will advance our knowledge of the 17β-HSD1 inhibitors and offer clues to developing new 17β-HSD1 inhibitors for future applications.

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

Anion photoelectron spectroscopy and theoretical calculations of Cu4On -/0 (n = 1-4): Identification of stable quasi-square structure for Cu4O4.

We investigated Cu4On - (n = 1-4) clusters through a synergetic combination of mass-selected anion photoelectron spectroscopy and density functional theory calculations. It is found that the most stable structure of Cu4O- is an irregular planar pentagon with a Cs symmetry. Those of Cu4O2 - and Cu4O3 - are non-planar structures with a Cs symmetry. The global minimum geometry of Cu4O4 - is a D4h symmetric quasi-square eight-membered ring with Cu-O bond lengths of ∼1.78 Å. The molecular orbital analyses suggest that Cu4O4 - has a large highest occupied molecular orbital and lowest unoccupied molecular orbital gap. The chemical bonding analyses and the calculations of the magnetically induced current density, and NICS(0) and NICS(1) values indicate that the D4h structure of Cu4O4 - is very stable and it has some aromaticity.

Clarifying the Adsorption of Triphenylamine on Au(111): Filling the HOMO–LUMO Gap

In this article, we analyze the electronic structure modifications of triphenylamine (TPA), a well-known electron donor molecule widely used in photovoltaics and optoelectronics, upon deposition on Au(111) at a monolayer coverage. A detailed study was carried out by synchrotron radiation-based photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy (STM), and ab initio calculations. We detect a new feature in the pre-edge energy region of the N K-edge NEXAFS spectrum that extends over 3 eV, which we assign to transitions involving new electronic states. According to our calculations, upon adsorption, a number of new unoccupied electronic states fill the energy region between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the free TPA molecule and give rise to the new feature in the pre-edge region of the NEXAFS spectrum. This finding highlights the occurrence of a considerable modification of the electronic structure of TPA. The appearance of new states in the HOMO–LUMO gap of TPA when adsorbed on Au(111) has crucial implications for the design of molecular nanoelectronic devices based on similar donor systems.

Synthesis of cholesterol containing unsymmetrical dimers: a new series of liquid crystals

ABSTRACT We report an efficient and practical procedure for the synthesis of cholesterol containing unsymmetrical liquid crystals dimers. Liquid crystalline and thermal properties were studied by POM, TGA, DSC, and SAXS analysis. All final products (3a-d) presented liquid crystal properties. The presence of smectic (compounds 3a, 3b, and 3d) and chiral nematic (3 c) mesophases evidenced by polarised optical microscopy (POM) and further confirmed by small-angle X-ray scattering (SAXS) analyses. The compound 3 c remains supercooled until room temperature and presented enantiotropic mesomorphism at a low temperature. This characteristic of organisation and mesomorphism at room temperature makes compound 3 c an ideal candidate for technological applications. The SAXS analyses further suggest possibly the presence of smectic clusters within the nematic liquid crystalline phase. All compounds presented high thermal stability at around 300°C when tested for their thermal properties. The highest occupied molecular orbital (HOMO) energies were estimated from cyclic voltammetry (CV) and used together with the optical absorption measurements to determine the band gap and lowest unoccupied molecular orbital (LUMO) energies. The values obtained were: HOMO (–5.81 to – 6.03 eV), LUMO (–1.53 to – 2.12 eV), and band gap (3.88 to 4.28 eV).

Electronic levels of small molecules for organic solar cells: A computational study

Currently significant progress has been made for the small molecules, indeed, achieved comparable performance compared to polymer in electronic devices mainly due to the many advantages of small molecules over the polymers. Designing better small molecules for electronic applications are required a comprehensive understanding of the structure-properties relationship and the factors affecting it. Valuable information can be generated directly toward understanding by systematically theoretical and experimental studies (band gap, HOMO, LUMO energy levels and geometry). Hybrid density functional B3LYP level of theory is a very good method for predicting the reliable geometry, electronic structure and properties of conjugated systems. In the present work, we have calculated the band gaps, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and geometry of a series of small molecules based on oligothiophene, benzodithiophene and dithienosilole unit using the hybrid density functional (B3LYP/6-31G(d)) level of theory and correlated with experimental values. The study provides details for the effect of the extended conjugation, two-dimension conjugation, substitution on geometry, HOMO, LUMO and band gaps of the small molecules. Copyright © 2017 VBRI Press.

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Aggregation-Induced Fluorogens in Bio-Detection, Tumor Imaging, and Therapy: A Review

Quantification of the Properties of Organic Molecules Using Core‐Loss Spectra as Neural Network Descriptors

Artificial neural networks are applied to quantify the properties of organic molecules by introducing a new descriptor, a core‐loss spectrum, which is typically observed experimentally using electron or X‐ray spectroscopy. Using the calculated C K‐edge core‐loss spectra of organic molecules as the descriptor, the neural network models quantitatively predict both intensive and extensive properties, such as the gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) (HOMO–LUMO gap) and internal energy. The prediction accuracy estimated by the mean absolute errors for the HOMO–LUMO gap and internal energy is 0.205 and 97.3 eV, respectively, which are comparable with those of previously reported chemical descriptors. This study indicates that the neural network approach using the core‐loss spectra as the descriptor has the potential to deconvolute the abundant information available in core‐loss spectra for both prediction and experimental characterization of many physical properties. The study shows the practical potential of machine‐learning‐based material property measurements taking advantage of experimental core‐loss spectra, which can be measured with high sensitivity, high spatial resolution, and high temporal resolution.

Shape, Electronic Structure, and Trap States in Indium Phosphide Quantum Dots

Localized states on undercoordinated atoms at the surface of a quantum dot (QD) can become electron or hole traps when the atomic orbitals involved fall within the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the material. Therefore, QDs of more covalent materials are predicted to be more sensitive to trap-state formation. Here, we analyze the relation between the presence of undercoordinated surface atoms and the formation of localized trap states for InP QDs by means of density functional theory. We argue that the requirement of charge neutrality limits the possible shapes cation-rich InP QDs can take, among which small cuboctahedrons and tetrahedrons of any size. We thus select both structures as InP model QDs and show that a complete InCl3 surface passivation results in an electronic structure with a clean, delocalized HOMO–LUMO gap in either case. Upon removal of InCl3 formula units from the InP cuboctahedron, hole traps linked to 2-coordinated surface P can form, a behavior similar to that of CdSe QDs. On the other hand, InCl3 displacement from the InP tetrahedron can lead to hole and electron traps, related to 2- or 3-coordinated surface P and 2-coordinated surface In, respectively. Since we obtain a very similar electronic structure of pristine InP and CdSe cuboctahedrons, we argue that the concept of ionicity provides little guidance to understand the enhanced sensitivity of InP to trap-state formation. Therefore, more apt descriptors are needed to predict the energetic position of atomic orbitals of uncoordinated atoms relative to the delocalized band-edge states.