Lowest Occupied Molecular Orbital Research Articles

Exploring the inhibitory action of betulinic acid on key digestive enzymes linked to diabetes via in vitro and computational models: approaches to anti-diabetic mechanisms

ABSTRACT Phytochemicals are now increasingly exploited as remedial agents for the management of diabetes due to side effects attributable to commercial antidiabetic agents. This study investigated the structural and molecular mechanisms by which betulinic acid exhibits its antidiabetic effect via in vitro and computational techniques. In vitro antidiabetic potential was analysed via on α-amylase, α-glucosidase, pancreatic lipase and α-chymotrypsin inhibitory assays. Its structural and molecular inhibitory mechanisms were investigated using Density Functional Theory (DFT) analysis, molecular docking and molecular dynamics (MD) simulation. Betulinic acid significantly (p < 0.05) inhibited α-amylase, α-glucosidase, pancreatic lipase and α-chymotrypsin enzymes with IC50 of 70.02 μg/mL, 0.27 μg/mL, 1.70 μg/mL and 8.44 μg/mL, respectively. According to DFT studies, betulinic acid possesses similar reaction in gaseous phase and water due to close values observed for highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) and the chemical descriptors. The dipole moment indicates that betulinic acid has high polarity. Molecular electrostatic potential surface revealed the electrophilic and nucleophilic attack-prone atoms of the molecule. Molecular dynamic studies revealed a stable complex between betulinic acid and α-amylase, α-glucosidase, pancreatic lipase and α-chymotrypsin. The study elucidated the potent antidiabetic properties of betulinic acid by revealing its conformational inhibitory mode of action on enzymes involved in the onset of diabetes.

Nitrogen adsorption on Nb2C6H4+ cations: the important role of benzyne (ortho-C6H4).

N2 adsorption is a prerequisite for activation and transformation. Time-of-flight mass spectrometry experiments show that the Nb2C6H4+ cation, resulting from the gas-phase reaction of Nb2+ with C6H6, is more favorable for N2 adsorption than Nb+ and Nb2+ cations. Density functional theory calculations reveal the effect of the ortho-C6H4 ligand on N2 adsorption. In Nb2C6H4+, interactions between the Nb-4d and C-2p orbitals enable the Nb2+ cation to form coordination bonds with the ortho-C6H4 ligand. Although the ortho-C6H4 ligand in Nb2C6H4+ is not directly involved in the reaction, its presence increases the polarity of the cluster and brings the highest occupied molecular orbital (HOMO) closer to the lowest occupied molecular orbital (LUMO) of N2, thereby increasing the N2 adsorption energy, which effectively facilitates N2 adsorption and activation. This study provides fundamental insights into the mechanisms of N2 adsorption in "transition metal-organic ligand" systems.

Photoinduced energy transfer in sulfur-based heterocyclic compounds and corrole dyads

We have designed and synthesized three donor-acceptor systems in which corrole macrocycle is an energy acceptor and sulfur-based heterocyclic compounds such as thianthrene (S1-Cor), dibenzothiophene (S2-Cor) and benzothiophene (S3-Cor) are the donors at its meso phenyl position. The molecular integrity of all three D-A systems has been characterized by various spectroscopic techniques that include elemental analysis, 1H NMR and MALDI-MS. Differential functional theory studies suggest that the electron density of the highest occupied molecular orbital (HOMO) spread on both corrole and sulfur-substituted heterocyclic units whereas the lowest occupied molecular orbital (LUMO) spreads on corrole macrocycle only. Singlet excited state properties indicate that there is an efficient intramolecular photoinduced energy transfer (PEnT) from donor heterocyclic unit to corrole, when excited at [Formula: see text]290 nm. Förster theory was adopted to explain the PEnT reaction in these dyads. The time-correlated singlet photon counting (TCSPC) studies suggest that energy transfer rates ([Formula: see text] are found to be in the range of 1.06 × 109 S[Formula: see text] to 6.67 × 109 S[Formula: see text] and are solvent-dependent.

A COMPUTATIONAL DENSITY FUNCTIONAL THEORY INVESTIGATION OF THE INTERACTION OF BORON NITRIDE NANOSHEETS WITH MULTIPLE MOLECULAR HYDROGENS

In this study, the adsorption of molecular hydrogens (H2) on boron nitride (BN) frameworks was investigated using the density functional theory (DFT) technique. The results of optimized geometric structures revealed that molecular hydrogens were favourably adsorbed on top of nitrogen atoms in the BN monolayers. In addition, the optimized equilibrium geometries were utilized to calculate the electronic structures, including binding energies, energies of the highest and lowest occupied molecular orbitals (HOMO and LUMO), molecular electrostatic potentials (MEPs), and Mulliken atomic charges (MACs). The binding energy values were calculated to be approximately 0.01 eV per molecular hydrogen based on the results. As the number of molecular hydrogens increased in the BN framework, a slight increase was observed in the binding energy value per hydrogen molecule. Furthermore, the HOMO–LUMO gaps were determined with the corresponding energy values of about 6 eV. Regarding the Frontier molecular orbitals (FMOs) diagrams, the electron densities for the HOMOs of the studied systems were primarily focused on the N-edges. Conversely, for the LUMO, the electron density distribution was localized in the B-edges of titled systems. In the context of hydrogen adsorption on BN nanosheets, the MEP maps indicated that hydrogen atoms at the N-edges of the studied systems exhibited the most positive electrostatic potentials in this research. In contrast, surfaces with negative electrostatic potential surfaces were situated in the region close to B-edges. The computed results are consistent with the corresponding Mulliken atomic charge distributions. From the analyses of the Mulliken scheme, all nitrogen atoms displayed negative charge values, and positive charges were found on the boron atoms. The DFT results obtained in this report may serve as the foundation for developing hydrogen storage materials

A Smart Nanovector of Cationic Starch Modified Curcumin with Excellent Targeting and Sonodynamic Properties for Effective Therapy of MRSA‐Induced Osteomyelitis

AbstractDrugs treatment including antibiotics or herbal medicines cannot cure osteomyelitis effectively accompanied by drug‐resistance bacteria and even amputation after long‐term debridement. Herein, a materioherbological strategy is utilized to construct a smart nanovector of cationic starch (CS) modified curcumin nanoparticles (CS@Cur NPs) for treating methicillin‐resistant Staphylococcus aureus (MRSA) induced osteomyelitis. On the one hand, CS modification can reduce the π–π accumulation of curcumin to endow the nanocomposite with excellent water solubility. On the other hand, the hydroxyl group in the curcumin is hydrogen‐bonded to the carbonyl group in the monomer (methyl methacrylate, MMA) of CS, resulting in a decrease in both the bandgap (between the highest and lowest occupied molecular orbitals, labeled as ΔE) and the S1–T1 energy gap (ΔES‐T) while the spin–orbital coupling (SOC) values increase, which benefits the formation of triplet‐state molecules under ultrasonic irradiation, significantly improving the yields of reactive oxygen species (ROS) capacity. The CS@Cur NPs nanocomposite constructed in this paper produced a large number of ROS synergic targeting effects under continuous 15 min ultrasonic irradiation, the clearance rate of MRSA infection induced osteomyelitis in rats can be as high as 99.93%. This study provides a new therapeutic strategy for the treatment of osteomyelitis induced by pathogenic bacteria.

Analysis of Metal Clusters Based on Graph-Theoretic Interpretation of the Lowest Occupied Molecular Orbital

Molecules can be regarded as a kind of graph with atoms as vertices and bonds as edges. Therefore, it is possible to discuss the physical properties and reactivity of various molecules by applying the ideas of graph theory and network theory. Such research has flourished in the field of chemical graph theory. In this manuscript, it is shown that the lowest occupied molecular orbital (LOMO) can be interpreted graph theoretically as eigenvector centrality. This is one measure of centrality that characterizes the importance or influence of a node on a network. As such, LOMO coefficient can be regarded as a manifestation of centrality in an aggregate of atoms, indicating which atom plays the most important role in that aggregate or has the greatest influence on the atom network. Using such properties of LOMO, an analysis of the network of metal atoms in metal clusters is performed. The predictability of the binding energies of the constituent atoms of the metal clusters using LOMO coefficients is discussed.

Arginine-modified black phosphorus quantum dots with dual excited states for enhanced electrochemiluminescence in bioanalysis

The electrochemiluminescence (ECL) is generally emitted via radiative transition of singlet or triplet excited state (S1 or T1). Herein, an ECL mechanism with the transitions of both S1 and T1 of black phosphorus quantum dots (BPQDs) is found, and an arginine (Arg) modification strategy is proposed to passivate the surface oxidation defects of BPQDs, which could modulate the excited states for enhancing the ECL efficiency of BPQDs. The Arg modification leads to greater spatial overlap of highest and lowest occupied molecular orbitals, and spectral shift of radiative transitions, and improves the stability of anion radical of BPQDs. To verify the application of the proposed mechanism, it is used to construct a sensitive method for conveniently evaluating the inhibiting efficiency of cyclo-arginine-glycine-aspartic acid-d-tyrosine-lysine to cell surface integrin by using Arg containing peptide modified BPQDs as signal tag. The dual excited states mediated ECL emitters provide a paradigm for adjustable ECL generation and extend the application of ECL analysis.

Comparative study of symmetrical and asymmetrical B40 molecular junctions

This work investigates quantum transport in symmetrical and asymmetrical borospherene-based molecular junctions with adenine. Adenine is one of the four nucleobases of DNA and was selected because of its excellent transport properties. The density functional/non-equilibrium Green's function (DFT-NEGF) mathematical approach was utilized, which was further used to calculate quantum transport parameters including the I–V curve, transmission spectra, highest occupied molecular orbital (HOMO)–lowest occupied molecular orbital (LUMO) gap (HLG), differential conductance, and transmission pathways. We observed that both symmetrical and asymmetrical devices exhibit nonlinear behavior, thus leading to non-differential resistance. Also, the symmetrical B40 molecular device demonstrated reduced HLG relative to the asymmetrical B40 molecular device. This drop in HLG was due to a reduction in electron density. A high rectification ratio for the devices was observed at 0.2 V. Hence, symmetrical and asymmetrical B40 molecular junctions are potential candidates for use in future nanoscale devices.

Synthesis, antibacterial, antifungal and computational study of (E)-4-(3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-oxoprop-1-en-1-yl)benzonitrile

In the present work, synthesis, antibacterial, antifungal and computational study of synthesized (E)-4-(3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-oxoprop-1-en-1-yl)benzonitrile (DHDOBN) chalcone derivative were explored. The computational study of the DHDOBN was performed using density functional theory (DFT) with B3LYP functional and 6-31G(d,p) basis set combination. Theoretical investigations about UV–vis and FT-IR spectral investigation of the DHDOBN was reported using TD-DFT/B3LYP/6-31G(d,p) and B3LYP/6-31G(d,p) levels, respectively. The computed UV–vis and FT-IR absorption spectral properties accord well with the outcomes of the experiments. The formation of the charge separation state as a result of the successful migration of electrons from the donor to acceptor unit through the π-bridge was confirmed by the analysis of electronic properties, including the frontier molecular orbitals (FMOs) analysis, molecular electrostatic surface potential (MESP), hole density distribution (HDD), and electron density distribution (EDD) map. highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy values were used to compute the ionisation potential, electron affinity, electronegativity, chemical hardness and softness, global electrophilicity, and chemical potential of the titled compound. The examined compound's significant DFT features were compared with those of other compounds that have been previously reported. In compound DHDOBN strong electron-withdrawing –CN group present at the para position makes the titled compound kinetically more reactive. The small EHOMO and ELUMO energy gap due to cyano group makes it soft and more polarizable molecule. The DHDOBN compound was tested for antibacterial activity against two Gram-negative bacterial strains namely E. coli and P. Vulgaris and two Gram-positive bacterial strains namely S. aureus and B. subtilis, whereas fungal inhibitory action was tested against A. Niger and C. albicans. The DHDOBN compound was revealed to show moderate antibacterial and antifungal potential.

Polyarylether-Based 2D Covalent-Organic Frameworks with In-Plane D-A Structures and Tunable Energy Levels for Energy Storage.

The robust fully conjugated covalent organic frameworks (COFs) are emerging as a novel type of semi‐conductive COFs for optoelectronic and energy devices due to their controllable architectures and easily tunable the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) levels. However, the carrier mobility of such materials is still beyond requirements due to limited π‐conjugation. In this study, a series of new polyarylether‐based COFs are rationally synthesized via a direct reaction between hexadecafluorophthalocyanine (electron acceptor) and octahydroxyphthalocyanine (electron donor). These COFs have typical crystalline layered structures, narrow band gaps as low as ≈0.65 eV and ultra‐low resistance (1.31 × 10−6 S cm−1). Such COFs can be composed of two different metal‐sites and contribute improved carrier mobility via layer‐altered staking mode according to density functional theory calculation. Due to the narrow pore size of 1.4 nm and promising conductivity, such COFs and electrochemically exfoliated graphene based free‐standing films are fabricated for in‐plane micro‐supercapacitors, which demonstrate excellent volumetric capacitances (28.1 F cm−3) and excellent stability of 10 000 charge–discharge cycling in acidic electrolyte. This study provides a new approach toward dioxin‐linked COFs with donor‐acceptor structure and easily tunable energy levels for versatile energy storage and optoelectronic devices.

Organic Dyes in Dye-Sensitized Solar Cells Featuring Back Reflector

Dye-sensitized solar cells (DSSCs) were fabricated using a photoelectrode covered by a porous layer of titanium dioxide, platinum counter electrode, iodide/triiodide electrolyte and three different dyes: phenylfluorone (PF), pyrocatechol violet (PCV) and alizarin (AL). After the adsorption of the dyes on the mesoporous TiO2 layer, the measurement of absorption spectra of all the tested dyes revealed a significant broadening of the absorption range. The positions of highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) levels of dye molecules were determined, indicating that all three dyes are good candidates for light harvesters in DSSCs. The cells were tested under simulated solar light, and their working parameters were determined. The results showed that the implementation of the back reflector layer made of BaSO4 provided an improvement in the cell efficiency of up to 17.9% for phenylfluorone, 60% for pyrocatechol violet and 21.4% for alizarin dye.

Molecular modeling and antioxidant evaluation of new di-2-thienyl ketones festooned with thiazole or pyridine moiety

• Synthesis of new functionalized dithienyl ketones linked thiazole and/or pyridine. • The DFT study was conducted to determine the HOMO-LUMO energies and Fukui's indices. • The local relative electrophilicity and nucleophilicity descriptors were calculated. • Antioxidant activity of the synthesized dithienyl ketone derivatives was explored. • The computational docking processes were examined toward (PDB Code: 2AS1). Different novel derivatives of 5-(5-bromothiophen-2-oyl)-2-(phenylamino)thiophen-3-yl) ethylidene-hydrazinylthiazole and 2-(5-bromothiophen-2-oyl)thieno[2,3-b]pyridine were prepared by utilizing the synthesized (5-bromothien-2-yl) (4-acetyl-3-methyl-5-phenylaminothien-2-yl) ketone (3) as a precursor. The electronic and chemical reactivity of the derivatives toward nucleophilic, electrophilic, and radical attacks were evaluated based on quantum chemical calculations; the highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) energies and Fukui indices were determined using the density functional theory (DFT) at Becke, 3-parameter, Lee–Yang–Parr (B3LYP) level. Compound 6 possessed the lowest HOMO energy value (E H ), LUMO energy value (E L ), and energy gap (ΔE H-L ). Significant inhibition percentage was observed while evaluating the antioxidant activities of the synthesized di-2-thienyl ketones 3–8 using vitamin C as a reference drug. The highest antioxidant activity with an IC 50 value of 39.85 and 34.37 µM was observed for the di-2-thienyl ketones 5 and 6 incorporating thiazole ring. Meanwhile, the rest of the di-2-thienyl ketone derivatives displayed reasonable IC 50 values from 51.60 to 68.88 µM. This experimental data was supported by molecular docking analysis of the interactions between di-2-thienyl ketone compounds and cytochrome c peroxidase (PDB Code: 2AS1) applied through Molecular Operating Environment (MOE) v10.2015.10.

Determination of electronic characteristics of tetrahydro pyrimidine derivatives and investigation of usability as anti-corrosion

Corrosion of metallic structures is a serious problem in most industries worldwide. This problem can be controlled by the addition of chemicals capable of adsorption onto the metal surface. The metal can be isolated from the corrosive environment. These chemicals are often selected from groups containing free electron pairs and / or π electrons, which are rich in functional groups. In this study, electronic structures Highest Molecular Orbital (HOMO), Lowest Occupied Molecular Orbital (LUMO), MEP, energy gap (ΔE), ionization potential (I), electron affinity (A), chemical structure of pyrimidine derivative compounds containing unpaired electron pairs, π electrons, functional groups such as N, O and S hardness and softness (S), general electrophilic index (ω), transmitted electron fraction index (ΔN) and recovery (backEback-donation) properties of quantum chemical calculation methods to investigate the properties of the selected compounds in this direction and adsorbed to the surface with the quantum chemical calculation methods. The aim of this study is to determine the efficiency of synthesized compounds as anti-corrosion materials and to provide new gains to the industry in this sense.

Intramolecular Photo-Oxidation as a Potential Source to Probe Biological Electron Damage: A Carboxylated Adenosine Analogue as Case Study.

A carboxylated adenosine analog (C-Ado−) has been synthesized and probed via time-resolved photoelectron spectroscopy in order to induce intra-molecular charge transfer from the carboxylic acid moiety to the nucleobase. Intra-molecular charge transfer can be exploited as starting point to probe low-energy electron (LEE) damage in DNA and its derivatives. Time-dependent density functional theory (TD-DFT) calculations at the B3LYP-6311G level of theory have been performed to verify that the highest occupied molecular orbital (HOMO) was located on carboxylic acid and that the lowest occupied molecular orbital (LUMO) was on the nucleobase. Hence, the carboxylic acid could work as electron source, whilst the nucleobase could serve the purpose of electron acceptor. The dynamics following excitation at 4.66 eV (266 nm) were probed using time-resolved photoelectron spectroscopy using probes at 1.55 eV (800 nm) and 3.10 eV (400 nm). The data show rapid decay of the excited state population and, based on the similarity of the overall dynamics to deoxy-adenosine monophosphate (dAMP–), it appears that the dominant decay mechanism is internal conversion following 1ππ* excitation of the nucleobase, rather than charge-transfer from the carboxylic acid to the nucleobase.

Perspective of Zn3O3 ring cluster via density functional theory

ZnO is well known for its optical properties and broad application. Although it has been investigated extensively, information regarding Zn3O3 clusters in the form of a ring is insufficient. This paper discusses the extraction of a ZnO ring as a Zn3O3 cluster comprising three molecules obtained from a 2 × 2 × 2 zincite supercell and its optimized normal, cationic, and anionic forms under the density functional theory framework. Its geometric and electronic structures as well as electronically excited states are investigated based on electronic spectra. Furthermore, the density of states, transition densities of molecular orbitals, highest and lowest occupied molecular orbitals, lowest unoccupied molecular orbitals, gap energies, binding energies, ionization potential, electron affinity, and quantum descriptors are investigated. Significant changes in the ultraviolet (UV)–visible absorption spectra are reported based on time-dependent density functional theory. Weak interactions by non-covalent interactions in Zn3O3 are investigated for the first time in this study; variations in the electrostatic potential are also discussed. The stable form ring and its formation are investigated using thermodynamic potentials U, H, and G (with additional parameters such as zero-point energy and entropy), which are obtained through frequency optimization. The rings investigated from the Zn3O3 cluster suggest some possibilities, such as the tuning of UV to visible light absorption.

Adsorption and corrosion inhibition accomplishment for thiosemicarbazone derivatives for mild steel in 1.0 M HCl medium: Electrochemical, XPS and DFT studies

Four benzaldehyde thiosemicarbazone derivatives namely as 2-benzylidene-N-phenylhydrazinecarbothioamide (L1), 2-(4-hydroxybenzylidene)-N-phenylhydrazinecarbothioamide (L2), 2-(4-chlorobenzylidene)-N-phenylhydrazinecarbothioamide (L3), and 2-(4-methylbenzylidene)-N-phenylhydrazinecarbothioamide (L4) were successfully synthesized and elucidated by physical and spectral techniques, to be specific, melting point, elemental analysis (CHNS), infrared spectroscopy (FTIR) and 1H and 13C nuclear magnetic resonance spectroscopy (NMR). These organic corrosion inhibitors behaviour for mild steel (MS) in 1.0 M HCl solution was examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. From the electrochemical measurements, most ligands behave as efficient inhibitors for the MS in 1.0 M HCl solution which contribute the maximum inhibition efficiency up to 93.38% for L3. The potentiodynamic polarization measurements unfolds each synthesized compound were mixed-type inhibitor based on the shifting of corrosion potentials (Ecorr) found to be lesser than ±85 mV. The electrochemical impedance spectroscopy (EIS) analysis revealed retardation of metal corrosion succeeded by cause of adsorption of the four thiosemicarbazone derivatives inhibitor molecules at the metal/solution interface. The adsorption of thiosemicarbazone molecules on the low carbon steel surface in 1.0 M HCl solution obeys Langmuir adsorption isotherm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrates in the presence of optimum concentration of L1-L4 inhibitors at 0.04 mM indicates greatly reduced surface roughness of MS in comparison with uninhibited solution. The findings were further reinforced via surface elemental analysis of metal/solution interface via X-ray Photoelectron Spectroscopy (XPS), which unveils L3 exhibit the greatest inhibition efficiency. The most plausible reason is due to benzene rings in the molecular structure increases the adsorption ability in supporting the substituent of chloro as well as conjugated double bond of C=N and C=S that chemisorbed along the surface of metal. The oxide species of FeO, Fe2O3 and FeOOH found to be chemisorbed and physisorbed on MS surface. The impact of molecular properties on the corrosion inhibition and the adsorbed sites of L1-L4 on the metal were investigated using density functional theory calculations (DFT) at the B3LYP/6–311 + G (d,p) level of theory. From the Frontier Molecular Orbitals (FMO), the Highest Occupied Molecular Orbitals (HOMO) discloses adsorption of L2 on the MS surface generally due to 2-(4-hydroxybenzylidene)-N-hydrazinecarbothioamide, whereas for L1, L3 and L4 associated to the inclusion of phenyl carbothioamide. The Lowest Occupied Molecular Orbitals (LUMOs) of L1-L4 are comparatively resembling and delocalized of all molecules. DFT reveals protonated thiosemicarbazones exhibits high correlations coefficients as up to 99–100% in comparison to the corresponding neutral forms of the molecules. The increase in the inhibition efficiency of protonated L1, L2 and L3 is proportional to the ∆N and DM.

From Infection Clusters to Metal Clusters: Significance of the Lowest Occupied Molecular Orbital (LOMO).

In this paper, the nature of the lowest-energy electrons is detailed. The orbital occupied by such electrons can be termed the lowest occupied molecular orbital (LOMO). There is a good correspondence between the Hückel method in chemistry and graph theory in mathematics; the molecular orbital, which chemists view as the distribution of an electron with a specific energy, is to mathematicians an algebraic entity, an eigenvector. The mathematical counterpart of LOMO is known as eigenvector centrality, a centrality measure characterizing nodes in networks. It may be instrumental in solving some problems in chemistry, and also it has implications for the challenge facing humanity today. This paper starts with a demonstration of the transmission of infectious disease in social networks, although it is unusual for a chemistry paper but may be a suitable example for understanding what the centrality (LOMO) is all about. The converged distribution of infected patients on the network coincides with the distribution of the LOMO of a molecule that shares the same network structure or topology. This is because the mathematical structures behind graph theory and quantum mechanics are common. Furthermore, the LOMO coefficient can be regarded as a manifestation of the centrality of atoms in an atomic assembly, indicating which atom plays the most important role in the assembly or which one has the greatest influence on the network of these atoms. Therefore, it is proposed that one can predict the binding energy of a metal atom to its cluster based on its LOMO coefficient. A possible improvement of the descriptor using a more sophisticated centrality measure is also discussed.

Comparative studies of excited state intramolecular proton transfer (ESIPT) and azo-hydrazone tautomerism in naphthalene-based fluorescent acid azo dyes by computational study

Abstract We found that benzothiazole is responsible for enhancing fastness properties of dyes. On comparing the total electronic energies of naphthol tautomers (−1425.16 eV) and its analogs (−2146.59 eV), we found that benzothiazolyl series is more stable than the naphthol series. Frontier Molecular Orbitals (FMOs) also show flow of charge transfer from the donor to the acceptor in benzothiazole-containing compounds, whereas it is absent in plane naphthol series. Among the benzothiazolyl isomers, the hydrazone form is found to be more stable and responsible for fluorescence possession. Highest Occupied Molecular Orbital (HOMO)–Lowest Occupied Molecular Orbital (LUMO) energy band gap also indicates the same. Electrophilicity index and hyper-hardness values of both the series were found to be positive which directly ratifies photostability and reactivity. Benzothiazolyl series was found to be more stable, hence light fastness, enhanced.

Theoretical Study of Phenoxaphosphine-Based Blue Organic Light-Emitting Diode Exhibiting Thermally Activated Delayed Fluorescence.

We designed novel thermally activated delayed fluorescence (TADF) materials by combining the electron donors spiro[acridine-9,9'-fluorene] (D1) and 9,9-diphenyl acridan (PAC) with the electron acceptor phenoxaphosphine (OPO) unit (2D1-OPO and 2PAC-OPO) and used those property to compare it with that of the reference material using dimethylacridan (Ac) as an electron donor (Ac-OPO) for blue organic light-emitting diodes (OLEDs). To calculate electron distribution of highest occupied molecular orbitals (HOMO), lowest occupied molecular orbital (LUMO), lowest singlet (S1) energy and lowest triplet (T1) excitation states, density functional theory (DFT) and time-dependent DFT calculation have been used. The calculated energy difference (ΔEST) between the S1 and T1 states of 2D1-OPO (0.125 eV) and 2PAC-OPO (0.153 eV) were as small as that of Ac-OPO (0.127 eV). The results showed that 2D1-OPO is a good candidate for blue OLED emitter because it has an emission wavelength of 441.0 nm as well as a sufficiently small ΔEST value and large oscillator intensity value.

Underlying Mechanisms on Tunable Electronic Structures of Graphene Quantum Dots Doped with Nitrogen and Sulfur Heteroatoms

Graphene quantum dots (GQDs) are a new class of quantum dots with unique chemical and physical properties, and significant developments have been made on their electronic characteristic structures for wide applications in electronics, energy conversion and storage devices. Doping heteroatoms into graphene nanostructures is an efficient way to tune electronic structures. However, different synthesis methods have resulted in different doping configurations to affect electronic properties and thereby hindered systematically understanding the mechanisms of GQDs doped with heteroatoms. Herein, the electronic mechanism of GQDs doped with N and S was studied by density functional theory (DFT). The formation energies, electronic structures, and electrostatic potentials of the doped GQDs were calculated to reveal effects of different doping types on electronic properties. For the N/S co-doped GQDs, graphitic N and pyridine N were considered to substitute carbon atoms in the plane while the -C-S-C- and -C-SO2-C- at the edge. The formation energy calculated by DFT indicates that heteroatom doping tends to be doped at the basal plane. And surface doping could increase charge density of carbon atoms connected to nitrogen atoms. The introduction of -C-S-C- into the graphitic N and pyridine N structures reduces the energy difference between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO). However, the addition of oxidized S into the N-doped structure increases the HOMO–LUMO energy gap. For the electrostatic potential diagram, the introduction of sulfur-containing groups can enhance the charge density around nitrogen, which suggests that heteroatom co-doped GQDs have improved electron transports. Therefore, this work provides valuable information on understanding electronic properties of N/S co-doped GQDs for the applications in nanoelectronic devices and give guidance for developing methods to controllably synthesize GQDs with well-defined and desirable properties towards specific purposes.