Frontier Orbital Energies Research Articles

Electrostatically driven energy shift of molecular orbitals of benzene and nicotine in carbon nanotube gaps

The requirement for controllable frontier orbital energy shift in single-molecule devices based on electronic (tunneling) transport yielded several rules for device design that lean on molecular level pinning to the electrochemical potential of nano-electrodes. We previously found that the pinning (designated as the strong pinning) was the consequence of the bias-induced molecular charge accumulation related to the hybridization of the highest occupied molecular orbital (HOMO) with one of the electrodes. However, in the wide bias range, only “partial” pinning (designated as the weak pinning) happens. In this work, we address the bias-induced shift of molecular orbitals in a weak pinning regime, where no hybridization or covalent bonds with electrodes exist. We found using density functional theory coupled with non-equilibrium Green’s functions that the energy shift of frontier molecular orbitals of benzene and nicotine, placed between H-terminated (3, 3) CNTs, in weak pinning regime, is driven only by the electrostatic potential energy of an empty gap. For nicotine, whose HOMO and LUMO (lowest unoccupied molecular orbital) are located on different sides of the gap center, we show that the HOMO-LUMO energy gap changes with bias. We developed a theoretical model of a dielectric in a gap to depict this behavior. Application-wise, we expect that the weak pinning effect would be observable in novel single-molecule sensors based on electronic transport and molecular rectifying as long as the system exhibits a non-resonant behavior, and could serve for molecular gap tuning in single-molecule readout such as DNA, RNA and protein sequencing, or harmful single-molecule detection in gas phase.

Energy profile, structure, spectroscopic and quantum chemical investigations of trans–3,4–(methylenedioxy)cinnamic acid

Abstract The molecular structural parameters and thermodynamic properties of trans–3,4–(methylenedioxy)cinnamic acid have been determined by B3LYP method by using 6–311++G** and cc–pVTZ basis sets. The vibrational frequencies of the compound have been precisely assigned, analysed and the theoretical results are compared with FT-IR and FT-Raman data. The energies of important MOs of the compound are also evaluated from DFT method. The frontier orbital energy gap (ELUMO–EHOMO) is found to be 4.1032 eV. The hydrogen and carbon chemical shifts are elaborately discussed. The dual descriptors Δfk, Δsk and Δωk reveals that the order of reactivity towards nucleophilic attack is C1 > O13 > O12 > C3 > C8 > C6. The minimum and maximum limits of the electrostatic potential observed in MDCA is –1.448e × 10–2(red) and +1.448e × 10–2 (blue). Thus, the present investigation provides complete structural, vibrational and reactivity characteristics of the compound .

Cyclometalation in the (η3-C5H5)Co(η2-C2H2)(PMe3) and (η3-C9H7)Co(η2-C2H2) (PMe3) complexes: A computational investigation

This research examined the cyclometalation in the (η3-C5H5)Co(η2-C2H2)(PMe3) and (η3-C9H7)Co(η2-C2H2)(PMe3) complexes by using mPW1PW91 functional. Thermodynamic and kinetic parameters of this reaction were computed. The solvent effects were studied by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and reactivity parameters (hardness, chemical potential, electrophilicity). The Hirshfeld population analysis was performed based on optimized structures. The rate constant of the cyclometalation reaction was computed from 300 to 1200 K, in the gas phase. In addition, the synchronicity values of this reaction were determined. Our findings revealed, this reaction was favorable energetically in both gas and solution phases. The larger rate constant values were in the presence of Cp ring than In ring.

New Application of 1,2,4-Triazole Derivatives as Antitubercular Agents. Structure, In Vitro Screening and Docking Studies.

A series of 1,2,4-triazole derivatives were synthesized and assigned as potential anti-tuberculosis substances. The molecular and crystal structures for the model compounds C1, C12, and C13 were determined using X-ray analysis. The X-ray investigation confirmed the synthesis pathway and the assumed molecular structures for analyzed 1,2,4-triazol-5-thione derivatives. The conformational preferences resulting from rotational degrees of freedom of the 1,2,4-triazole ring substituents were characterized. The lipophilicity (logP) and electronic parameters as the energy of frontier orbitals, dipole moments, NBO net charge distribution on the atoms, and electrostatic potential distribution for all structures were calculated at AM1 and DFT/B3LYP/6-311++G(d,p) level. The in vitro test was done against M. tuberculosis H37Ra, M. phlei, M. smegmatis, and M. timereck. The obtained results clearly confirmed the antituberculosis potential of compound C4, which turned out to be the most active against Mycobacterium H37Ra (MIC = 0.976 μg/mL), Mycobaterium pheli (MIC = 7.81 μg/mL) and Mycobacerium timereck (62.6 μg/mL). Satisfactory results were obtained with compounds C8, C11, C14 versus Myc. H37Ra, Myc. pheli, Myc. timereck (MIC = 31.25−62.5 μg/mL). The molecular docking studies were carried out for all investigated compounds using the Mycobacterium tuberculosis cytochrome P450 CYP121 enzyme as molecular a target connected with antimycobacterial activity.

DFT calculations on molecular structure, MEP and HOMO-LUMO study of 3-phenyl-1-(methyl-sulfonyl)-1H-pyrazolo[3,4-d]pyrimidine-4-amine

Electronic structure calculation explores the molecular structure and geometric conformations of the molecules from only the knowledge of its constituent atoms. In the present work, quantum mechanical calculations of a 3-phenyl-1-(methyl-sulfonyl)-1H-pyrazolo[3,4-d]pyrimidine-4-amine molecule have been performed by Density Functional Theory using the standard 6-31G** basis set with the GAUSSIAN09. The electronic structure, dipole moment, frontier orbitals energy, thermal parameters (entropy, enthalpy, internal energy, and Gibb’s potential), Infrared (IR) spectral lines of the title molecule are elaborated. To study the chemical reactivity; molecular electrostatic potential (MEP) surface, HOMO-LUMO surface, and some other properties of the molecule were also investigated.

Analysis of Bonding Properties of Osmabenzyne in the Ground State (S0) and Excited Singlet (S1) State: A Quantum-Chemical Calculation

The hybrid density functional MPW1PW91 theory was applied in the ground state (S0) and first excited singlet (S1) state to highlight the structure, electronic properties, and aromaticity of an osmabenzyne complex. The first singlet excited state was determined by time-dependent DFT (TD-DFT) method. It was tried to explore the geometry, frontier orbital energies, reactivity indices, and aromaticity in the first singlet excited state of osmabenzyne complex and compare to ground state. Moreover, this study determined the involvement of the fragments of the studied complexes in the frontier orbitals regarding the ground state and first singlet excited state. Energy decomposition analysis (EDA) for S0 and S1 states was applied to study the nature of the chemical bond between the [Os (PH3)2Cl2]2+ and [C5H4]2– fragment. ‎In addition, the Os–C, Os–Cl, and Os–P bonds in the studied osmabenzyne were clarified using quantum theory of atoms in molecules analysis (QTAIM) calculations.

STRUCTURE OF IONS AND THE ENERGY OF THEIR FORMATION IN SATURATED ALUMINUM TRIS- DIPIVALOYLMETHANATE VAPOR UPON ELECTRON IONIZATION

The DFT/B3LYP method is used to study geometric and electronic structures of ions formed in the mass spectrum upon electron ionization of molecular forms in the vapor of aluminum tris-dipivaloylmethanate (Al(C11H19O2)3, Al(dpm)3). It is shown that the most energetically favorable processes upon dissociative ionization of molecular form AlL3 (L = dpm) are related to the detachment of radicals CH3•, t-Bu• and the anionic form of the ligand dpm–. It is established that one chelate ring is broken upon the formation of ions [AlL3–t-Bu]+, [AlL3–2t-Bu]+, [AlL3–6t-Bu]+ and the structure of the latter contains one monodentate ligand and two bidentate ligands. In the ions with compositions [AlL2]+, [AlL2–CH3]+, [AlL2–2CH3]+, [AlL2–4CH3]+, and [AlL2–2t-Bu–CH3]+, the cores of two bidentate ligands are located in mutually perpendicular planes. The energies of reactions leading to the formation of the above ions are calculated. The energies of frontier orbitals of these ions are considered; the reasons of high-intensity [AlL2]+ current are revealed. Detailed examination of ions in the mass spectrum of aluminum tris-dipivaloylmethanate (a typical representative of tris-β-diketonate complexes) reveals a number of structural features that can be used to predict the structure of such ions in the mass spectra of numerous similar complexes belonging to the ML3 type.

Highly Purified Materials for Sn-and Pb-Based Perovskite Solar Cells

Perovskite solar cells are promising cost-effective next generation printable photovoltaics. These solar cells have attracted the interest of many researchers. Thanks to tremendous effort of the researchers in this field, the power conversion efficiencies (PCEs) have been substantially increased in a short period, which is mainly due to improvements of the fabrication protocols for the perovskite layer as well as the development of new materials for buffer layers.Our approaches toward efficient lead and lead-free perovskite solar cells are as follows: Development of highly-purified perovskite precursor materialsDevelopment of solution process fabrication methods for the perovskite layerDevelopment of organic semiconductors for efficient charge-collection layers We have synthesized lead-halide and tin halide complexes as purified precursors for perovskite materials, which were later commercialized by TCI and are now widely used in this field as standard precursor materials. We also focus on the intermediates formed during the film-growth and have developed efficient fabrication methods based on the formation mechanism. We have designed and synthesized novel pi-conjugated materials designed to control frontier orbital energy levels, molecular aggregation properties, and the interface with the perovskite layer.In this talk, our recent progress on tin halide perovskite solar cells as well as lead halide perovskites will be introduced.

Fate of Low-Lying Charge-Transfer Excited States in a Donor:Acceptor Blend with a Large Energy Offset.

In an effort to gain a comprehensive picture of the interfacial states in bulk heterojunction solar cells, we provide a combined experimental-theoretical analysis of the energetics and dynamics of low-lying electronic charge-transfer (CT) states in donor:acceptor blends with a large frontier orbital energy offset. By varying the blend composition and temperature, we unravel the static and dynamic contributions to the disordered density of states (DOS) of the CT-state manifold and assess their recombination to the ground state. Namely, we find that static disorder (conformational and electrostatic) shapes the CT DOS and that fast nonradiative recombination crops the low-energy tail of the distribution probed by external quantum efficiency (EQE) measurements (thereby largely contributing to voltage losses). Our results then question the standard practice of extracting microscopic parameters such as exciton energy and energetic disorder from EQE.

Synthesis and fluorescence properties of two dendritic molecules based on naphthalimide and triphenylamine.

Artificial light-harvesting systems have attracted great interest in biological photosynthesis and photo-voltaic devices areas due to their unique structures, easy purification, low-cost, and convenient processing abilities. Here, two dendritic molecules based on triphenylamine and naphthalimide have been designed and synthesized, their structures were confirmed by 1 H NMR, ESI-MS, and high resolution mass spectrometry. In these molecules, triphenylamine units perform as the electron donor moiety, and naphthalimide units perform as the electron acceptor. The obvious quenched fluorescence intensity and considerably shortened lifetime of the dendritic molecules combined with the molecular frontier orbital energy levels proved that the dendritic molecules not only are good candidates as hole-transporting materials but also are two excellent photo-induced electron transfer materials. Therefore, it is believed that these dendritic molecules have potential application value in photo-voltaic devices.

Design and Synthesis of Annulated Benzothiadiazoles via Dithiolate Formation for Ambipolar Organic Semiconductors.

Substituted 2,1,3-benzothiadiazole (BTD) is a widely used electron acceptor unit for functional organic semiconductors. Difluorination or annulation on the 5,6-position of the benzene ring is among the most adapted chemical modifications to tune the electronic properties, though each sees its own limitations in regulating the frontier orbital levels. Herein, a hitherto unreported 5,6-annulated BTD acceptor, denoted as ssBTD, is designed and synthesized by incorporating an electron-withdrawing 2-(1,3-dithiol-2-ylidene)malononitrile moiety via aromatic nucleophilic substitution of the 5,6-difluoroBTD (ffBTD) precursor. Unlike the other reported BTD annulation strategies, this modification leads to the simultaneous decrease in both frontier orbital energies, a welcoming feature for photovoltaic applications. Incorporation of ssBTD into conjugated polymers results in materials boasting broad light absorption, dramatic solvatochromic and thermochromic responses (>100 nm shift and a band gap difference of ∼0.28 eV), and improved crystallinity in the solid state. Such physical properties are in accordance with the combined electron-withdrawing effect and significantly increased polarity associated with the ssBTD unit, as revealed by detailed theoretical studies. Furthermore, the thiolated ssBTD imbues the polymer with ambipolar charge transport property, in contrast to the ffBTD-based polymer, which transports holes only. While the low mobilities (10-4 to 10-5 cm2 V-1 s-1) could be further optimized, detailed studies validate that the thioannulated BTD is a versatile electron-accepting unit for the design of functional stimuli-responsive optoelectronic materials.

Tetrabenzeneaza macrocycle: A novel platform for universal high-performance hole transport materials

In this research, a novel macrocycle containing tetrabenzeneaza has been developed as a novel building block for hole transport materials (HTMs). Benefiting from its unique highly twisted spatial configuration, this macrocycle exhibits high triplet energy level (ET) as well as high hole mobility. Based on this aza macrocycle, two hole transporting materials, namely 2TPATPCA and 2CzTPCA, were designed and synthesized. Both 2TPATPCA and 2CzTPCA possess enough ETs, appropriate frontier orbital energy levels as well as good thermal stability, which promote them as universal HTMs in multicolor phosphorescent organic light-emitting devices (PhOLEDs) and thermal activated delay fluorescence (TADF) OLEDs. High external quantum efficiencies (EQEs) were realized in OLEDs using the these two HTMs. For example, sky bule PhOLED with 2CzTPCA showed a significantly improved maximum EQE of 20.3% compared to that of the reference device using N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) (EQE of 14.2%) and 4,4′-Cyclohexylidenebis[N,N- bis(4-methyl phenyl)aniline (TAPC) (EQE of 12.2%). Green TADF OLED using 2CzTPCA as HTM also exhibit a much improved maximum EQE of 17.9% compared to that of the reference device based on NPB (EQE of 10.3%). These results indicate this tetrabenzeneaza macrocyclic is a promising building block for developing universal high-performance HTMs.

Bridge Resonance Effects in Singlet Fission.

A major benefit of intramolecular singlet fission (iSF) materials, in which through-bond interactions mediate triplet pair formation, is the ability to control the triplet formation dynamics through molecular engineering. One common design strategy is the use of molecular bridges to mediate interchromophore interactions, decreasing electronic coupling by increasing chromophore-chromophore separation. Here, we report how the judicious choice of aromatic bridges can enhance chromophore-chromophore electronic coupling. This molecular engineering strategy takes advantage of "bridge resonance", in which the frontier orbital energies are nearly degenerate with those of the covalently linked singlet fission chromophores, resulting in fast iSF even at large interchromophore separations. Using transient absorption spectroscopy, we investigate this bridge resonance effect in a series of pentacene and tetracene-bridged dimers, and we find that the rate of triplet formation is enhanced as the bridge orbitals approach resonance. This work highlights the important role of molecular connectivity in controlling the rate of iSF through chemical bonds and establishes critical design principles for future use of iSF materials in optoelectronic devices.

Structural (SC-XRD), spectroscopic, DFT, MD investigations and molecular docking studies of a hydrazone derivative

• MD simulations give the stability nature of molecules. • Single crystal XRD with spectroscopic analysis. • Nucleophilic and electrophilic sites are identified. • Studied NLO, MEP and NBO. • Docking identifies the pharmacological property. Single crystal XRD of 1,2-dihydro-1-phenyl-2,3-di methyl-4-[2′,4′-pentanedione- 3′-hydrazono] pyrazol-5-one (DPPH) is reported. It was characterized using quantum mechanical calculations for geometry and spectroscopic analysis. Frontier orbital energies are used to predict the energy properties and model the possible charge transfer within molecule. Frontier molecular Orbital (FMO) analysis indicates chemical reactivity and bioactivity. The molecular electrostatic potential (MEP) surface reveals the various reactive surfaces which is very important in deciding various biological activities. Docking was performed to examine binding areas of chemical compounds. Bioactivity scores indicate that the ligand's pharmacokinetic and pharmacological properties are sufficient which leads to potential drug agents being considered. The findings of the present study obtained theoretical wavenumbers were completely consistent with the results of experiments. Further molecular dynamics (MD) simulation is done to identify stable situation. Moreover, the molecular docking analysis proves that DPPH can act as potential inhibitors and paves the way for developing effective drugs.

Theoretical insights about inhibition efficiencies of some 8-Hydroxyqionoline derivatives against the corrosion of mild steel

ABSTRACT In the present study, we theoretically analysed the corrosion inhibition performances of some novel 8-Hydroxyqionoline derivatives, namely 5-(((2-hydroxyethyl) thio) methyl) quinolin-8-ol (Q-OH) and 5-(((2-aminoethyl) thio) methyl) quinolin-8-ol (Q-NH2) against the corrosion of mild steel. In the section about DFT and HF calculations of the study, quantum chemical descriptors like frontier orbital energies, HOMO–LUMO energy gap, chemical hardness, electronegativity, softness, chemical potential, electrophilicity, nucleophilicity, proton affinity, electrons transferred from inhibitor to metal surface, electron-donating power, electron-accepting power, dipole moment, polarisability regarding protonated and neutral forms of the mentioned molecules were calculated and commented. In the section including the use of Molecular Dynamics Simulation approach of the analysis, adsorption behaviours of studied organic molecules on Fe (110) surface were investigated. To detect the power of the interactions between novel 8-Hydroxyqionoline derivatives and the mentioned metal surface, adsorption energy and binding energy values were calculated. It is important to note that these resuls determined are in good agreement with experimentally observed results. In addition to these analyses made, the validities of chemical reactivity principles such as Maximum Hardness, Minimum Polarisability and Minimum Electrophilicity Principles in corrosion inhibition studies were also reported.

Frontier Orbital Energy-Customized Ionomer-Based Polymer Electrolyte for High-Voltage Lithium Metal Batteries.

The development of gel polymer electrolytes (GPEs) is considered to be an effective strategy to drive practical applications of high-voltage lithium metal batteries (HLMBs). However, rare GPEs that can satisfy the demands of HLMBs have been developed because of the limited compatibility with lithium anodes and high-voltage cathodes simultaneously. Herein, a novel strategy for constructing polymer matrixes with a customized frontier orbital energy for GPEs is proposed. The as-investigated polymer matrix (P(CUMA-NPF6))-based GPE (P(CUMA-NPF6)-GPE) obtained via in situ random polymerization delivers a wide voltage window (0-5.6 V vs Li+/Li), large lithium-ion transference number (tLi+, 0.61), and superior electrode/electrolyte interface compatibility. It is to be noted that such a tLi+ of P(CUMA-NPF6)-GPE, which is one of the largest tLi+ among high-voltage GPEs in a fair comparison, results from the high dissociation of lithium salts and effective anion immobilization abilities of P(CUMA-NPF6). Ultimately, the as-assembled HLMB delivers more enhanced cycle performance than its counterpart of commercial liquid electrolytes. It is also demonstrated that P(CUMA-NPF6) can scavenge the active PF5 intermediate generated in the electrolyte at the anode side, thus suppressing the PF5-mediated decomposition reaction of carbonates. This work will enlighten the rational structure design of GPEs for HLMBs.

Improving Both Electron and Hole Mobilities of an Ambipolar Polymer by Integrating Sodium Sulfonate‐Tethered Alkyl Side Chains†

Summary of main observation and conclusionHigh performance ambipolar organic semiconductors are highly desirable for organic logic circuits. Herein, we demonstrate the integration of sodium sulfonate (SS)‐tethered sidechains into a diketopyrrolopyrrole‐based ambipolar polymer (PDPP3T) can simultaneously improve its hole and electron transport performances either parallel or perpendicular to polymer film. Three SS‐functionalized polymers (PDPP3T‐xSS, x = 0.025, 0.05 and 0.10) were synthesized and studied. It was found that SS functionalization can reinforce interchain π‐π interactions, slightly lower frontier orbital energy levels, produce more rod‐like structures in film, and change chain‐packing from edge‐on to face‐on fashion, but has little influence on thermal properties. More interestingly, organic field‐effect transistors reported hole mobility of 0.27 ± 0.066 cm2·V–1·s–1 and electron mobility of 0.038 ± 0.016 cm2·V–1·s–1 for PDPP3T, while increased 2.4 and 5 folds to 0.64 ± 0.087 and 0.19 ± 0.051 cm2·V–1·s–1 for PDPP3T‐0.025SS, respectively. Moreover, PDPP3T‐xSS devices displayed reduced threshold voltages for both hole and electron transports. Meanwhile, space charge‐limited current method found SS functionalization achieved an order of magnitude increase in electron mobility and slight enhancement in hole mobility transporting perpendicular to polymer film. In‐depth investigations suggest such enhancements may originate from the joint actions of chain‐stacking modulation and ionic doping effect.

New possibilities of 2-pyranone derivatives – Thermal, optical and electrochemical properties

The paper contains a comprehensive study regarding the new possibilities of using 2-pyranone derivatives. In this work, six compounds of this type (including three electropolymerisable bithiophenyl's monomers) were synthesized in a one-step reaction with high yields ranging from 57% to 81%. The synthesized monomers of Bt-py-Bt (where Bt = 2,2′-bithiophene-5-yl, py = pyranone moiety) type were transformed into conducting polymers in an electrochemical oxidation process. The influence of the pyranone bridge on the stability, luminescent and (spectro)electrochemical behaviour was thoroughly studied. The polymers present extraordinary stability during both multiple n- and p-doping. The experimental results were also investigated theoretically, using the DFT approach. Calculations of the frontier orbital energies and the corresponding Eg value were done for each polymer using periodic boundary conditions. Finally, the electrochemical impedance spectroscopy measurements of polymeric films were done and evaluated.

ELECTRONIC ABSORPTION SPECTRA AND INTERMOLECULAR HYDROGEN BONDING IN MESOGEN–NONMESOGEN SYSTEMS

The TD-DFT/B97-D/6-311G** method is used to calculate the electronic absorption spectra of А⋯Х⋯А supramolecules with intermolecular hydrogen bonds (HBs), where А is 4-n-propoxycinnamic acid, Х is a nonmesogen molecule with bifunctional HB acceptors. Nonmesogens Х (B, C, D, E) consist of two pyridyl fragments connected by bridging groups of different natures: 4,4′-bipyridine (В), 1,2-bis(4-pyridyl)ethane (С), 1,2-bis(4-pyridyl)ethylene (D), 4,4′-azopyridine (Е). It is shown that the introduction of bridging groups (–CН2–CН2–, –CН=СН–, –N=N–) significantly affects the energy of frontier orbitals and electronic absorption spectra (EAS) of nonmesogens Х in the near-UV region. The EAS of two structural units A⋯В⋯A, A⋯A, which may be formed due to the self-assembly in two-component mesogen А–nonmesogen В systems, are compared. Due to hydrogen bonds (O–H⋯N and O–H⋯O), having different types and strengths in these complexes, the high-intensity band shifts to shorter wavelengths in complex А⋯В⋯А and to longer wavelengths in complex А⋯А with respect to the λ = 333 nm band of monomer А. It is shown that EAS of hydrogen-bonded complexes А⋯Х⋯А are not superpositions of EAS of individual components. The spectra show electronic transitions related to charge transfer between the components of the complexes. Using nonmesogens Х of different nature in supramolecules А⋯Х⋯А will allow one to change purposefully their electro-optical properties and to achieve intense absorption in particular regions of UV spectra.

Theoretical Prediction of Properties of Cyclopenta[b]pyrrol-2-one Derivatives

The geometrical structures of the cyclopenta[b]pyrrol-2-ones were optimized at the DFT/B3LYP/6-31G* level of theory, and the obtained structures were confirmed to be minima on the potential energy surface by frequency calculations. Based on the optimized configurations, electronic excitation and emission were studied with the TD-DFT method. The energy behavior of A, B, and C have been examined in the THF solvent using the polarizable continuum (PCM) model. Molecular frontier orbital energy levels, UV–Vis spectra, heat maps, and fluorescence properties were investigated in detail. Furthermore, based on an analysis of hydrogen bonding interactions between HIV-1 protease and compound C, it can be concluded that C is expected to form a stable hydrogen bonding with ILE 50. All the work in this paper provides a theoretical basis for the research on pyrrol-2-ones.