HOMO LUMO Differences Research Articles

Microwave-assisted Synthesis of 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh)

Background: Microwave synthesis has developed as a powerful tool for the cost-effective and greener synthesis of organic molecules, including quinazolines. Irradiation with microwave leads to the excitation of molecules and equitable distribution of thermal energy in a much shorter time than conventional synthesis. This results in shorter reaction time and, more often than not, higher efficiency Objective: The primary objective of the work presented in this article was to prepare hydrazine hydrate or thiourea derivative of quinazolines through microwave synthesis as small-molecule scaffolds for fur-ther need-based functionalisation, isolation, and characterisation. We, herein, report the synthesis of two quinazolinone derivatives of thiourea and hydrazine, 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh), respectively. Method: A multi-step synthetic strategy starting from anthranilic acid was employed to synthesise the small molecule quinazolinones 3-amino-2-phenylquinazolin-4(3H)-one (QH) and 4-oxo-2-phenylquinazoline-3(4H)-carbothioamide (QTh). The compounds were synthesised by reacting hydra-zine and thiourea with 2-benzamidobenzoyl chloride in DMF under microwave irradiation (800 W at 135 °C for 4 min) in the presence of potassium carbonate. The acid chloride was prepared by chlorination of 2-benzamidobenzoic acid, which in turn was synthesised from anthranilic acid by benzoylation. This method is an efficient alternative approach to synthesising quinazolinones from benzoxazin-4-ones. Results: We have successfully synthesised, isolated, and characterised the quinazolinone derivative QH (yield: 81%) and QTh (yield: 85%). The structures of the compounds were established through spectro-scopic techniques. Theoretical optimisation of the structures was also achieved using DFT. The HOMO-LUMO difference for QH and QTh was calculated to be 4.60 and 4.47 eV, respectively. Conclusion: The reported protocol is advantageous over conventional methods of quinazoline synthesis from benzoxazin-4-ones. The time required for the reaction is much less (4 min) as compared to the usual requirements of reflux (> 4 h); the higher energy gap of QH indicates greater stability than that of QTh.

Alkaline earth metals doped C2N with enhanced non-linear optical properties

ObjectiveIn quest of better non-linear optical materials, we investigated optical and NLO (non-linear optical) properties of (C2N) doped with alkaline earthrides (Be, Mg and Ca) designated as C1, C2 and C3, respectively MethodDensity functional theory (DFT) method was used with B3LYP/6–31 G (d, p) level of theory, to carry out geometry optimization and to determine the density of states(DOS), Transition density matrix (TDM), Non-covalent interaction (NCI), infrared (IR) analysis and electron density difference map EDDM. ResultsA significant narrowing of HOMO-LUMO difference gap was observed for every doped molecules with respect to pristine C2N. Bathochromic shift was observed in absorption profile for doped system near-infrared region. Dipole moment (μg) of doped molecules show elevated trend with highest 5.21 D for C2. Polarizability α0 values increased linearly down the group from C1 to C3 while remarkable elevation of first hyperpolarizabilty β0 values was observed, with highest values of 12213.63 au (C1) and 29768.91 au (C2) with basis set 6–31 + +G. Favorable optical and electronic properties of C1 and C2 were observed which suggested them as outstanding candidates for nonlinear optical (NLO) applications.

Electro-physical properties of GaAs nanoscopic clusters

The electric current through the Cu-GaAs-Cu nanoclusters and their quasi-bandgap widths (HOMO-LUMO differences) are calculated. The ab initio electron propagator theory (Green-Keldysh functions formalism) is implemented for the calculations (that has been never done before for Cu-As-Cu nanoclusters). The calculated current-voltage characteristics exhibit non-linear character with magnitudes of current reaching several pAs. The calculated quasi-bandgap width (HOMO-LUMO difference) of nanocluster exhibits solid-like behavior with the increase of nanocluster's size. The obtained dependencies and characteristics will be useful for semiconductor quantum-dots manufactures and practitioners in the field of semiconductor nanoelectronics and optoelectronics, in particular, for developers of EM radiation sources and detectors with frequency-tuning ability.

Synthesis, spectroscopic characterization, and SC-XRD study of one privileged heteronuclear Ni(II)/Hg(II)-Salen complex: An exclusive DFT outlook

A novel heteronuclear Salen complex, [NiHgCl2(L)] (1) (H2L = N,N′-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine) has been integrated using two different synthetic lines. The complex is characterized by various spectroscopic techniques, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and single-crystal X-ray diffraction (SC-XRD). Powder X-ray diffraction (PXRD) confirms complex phase purity and crystallinity. The scanning electron microscope and energy-dispersive X-ray analysis (SEM-EDX) identified the element’s chemical composition, morphology, and crystal size. X-ray diffraction revealed ligand released phenoxide-type deprotonated form [L]2− and had spent two pockets, N2O2 pocket occupied by Ni(II) comprises square planar geometry (NiN2O2). In contrast, Hg(II) occupies a large open O4 compartment accompanied by two chloride ions (HgO4Cl2), switching to achieve a trigonal prismatic structure. The close surveillance of the crystal structure discloses various non-covalent interactions like H-bonding, CH⋯π, and π⋯π. The complex’s geometry was fully optimized, employing the quantum chemistry method at the DFT/B3LYP with the 6-31G (d, p) basis set to divine the vibrational spectra, NMR chemical shifts, and solvent effect on the electronic properties. Natural Bond Orbital (NBO) dissected the stability of the molecular structure and the intermolecular orbital interactions. The highest stabilizing energy was 132.84 kcal/mol between the lone pair C12 and the antibonding of N7-C17 atoms. The Hirshfeld Surface (HS) is detectable that the H⋯N input is maximum than H⋯O. The electrophilic-nucleophilic sites, non-covalent interactions, and reactivity were investigated based on Molecular Electrostatic Potential (MESP), Reduced Density Gradient (RDG), atoms in a molecule (AIM), and the HOMO-LUMO difference. Eventually, a significant correlation was anticipated between theoretical and experimental spectroscopic criteria.

DFT and Molecular docking study of natural molecules proposed for COVID-19 treatment

Abstract Emergence and spread of corona virus disease 2019 (COVID-19), caused by severe respiratory syndrome coronavirus, is considered a public health emergency threatening global health systems, as of June, 2020, It caused a cumulative total of 9,033,423 confirmed cases and more than 469,539 deaths across 215 countries, person to-person transmission has being identified as the route for spreading. So far, the lack of effective vaccines for the treatment or prevention of Covid-19 has further worsened the situation. In this context, the present study aims to assess whether naturally occurring components have an antiviral effect via a computational modeling approach. Density Functional theory (DFT) was performed to estimate the kinetic parameters, frontier molecular orbitals, molecular electrostatic potential as well as chemical reactivity descriptors of various ligands. The results revealed that Crocin and Digitoxigenin exhibited a potential applicant with the lowest resistance to electronic charge transfer with a chemical hardness of 2.19eV and 2.96eV respectively, as well as the lowest HOMO-LUMO difference. In addition to the DFT calculation, a docking simulation study was conducted on the SARS-CoV-2 base protease (PDB: 6LU7) to determine the binding affinity of ligands. The findings show that Crocin exhibits the lowest binding energy of -8.1 Kcal/mol and may be a good inhibitor of CoV-2-SARS compared to hydroxychloroquine and chloroquine, which have a binding affinity of -5.4 and -4.9 Kcal/mol, respectively. The high binding affinity of L3 was assigned to the existence of 14 hydrogen bonds connecting the ligand to the critical amino acid residues of the receptor.

2,7,12,17-Tetra(2,5-thienylene)-substituted porphycenes

We report syntheses of thiophene and dithiophene-substituted porphycenes (ThPc and DThPc) at 2,7,12,17-positions by McMurry coupling. The crystal structure of ThPc revealed that the porphycene plane shows a highly planar structure, and the dihedral angles between the porphycene core and thiophene are relatively small at 21[Formula: see text] and 18[Formula: see text]. ThPc and DThPc exhibit red-shifted and broadened absorption because of the extension of [Formula: see text] conjugations through porphycene to the substituted thiophenes. We found that introduction of thiophene units onto porphycene results in decreasing the HOMO–LUMO differences effectively.

Energetics and Escape of Interchain-Delocalized Ion Pairs in Nonpolar Media.

The electron acceptor F4TCNQ p-dopes aggregates "nanowires" of poly(3-hexylthiophene) in nonpolar solvents but does not dope unaggregated chains. The standard free energy change for the charge transfer to form an ion pair is ΔG°et = -0.21 eV. The dissociation constant to produce free ions in toluene by DC conductivity is K°d = 1 × 10-8 ± 50% (ΔG°d = 0.48 ± 0.05 eV). This remarkably large K°d , for ions in such a low polarity medium, may reflect interchain delocalization of the hole. The particular characteristics of this material system enables determination of both ΔG°et and ΔG°d , to find the overall free energy change from the two neutral species to completely separated ions in nonpolar media. It is endergonic by +0.27 ± 0.05 eV in contrast to -0.6 eV estimated from reported HOMO LUMO differences, illustrating the challenges that persist in determining such energetics. Steady state microwave conductivity experiments on doped aggregates confirm that holes in the aggregates cannot easily escape their dopant counterion, but at higher dopant concentrations, holes become mobile. These results provide insight into the mechanisms of charge separation involving intermolecularly delocalized charges in nonpolar media, an integral process in organic photovoltaic devices and doped molecular films.

Porphycene-Diketopyrrolopyrrole Conjugates As p-Type Organic Solar Cell Materials

Porphycene is a constitutional isomer of porphyrin. Porphycene has a lower LUMO level and smaller HOMO-LUMO difference than porphyrin since its molecular symmetry is lower than that of porphyrin. 1 These properties have allowed us to explore the possible applications of porphycenes in the fields of photodynamic therapy (PDT), photoinactivation of viruses and bacteria, protein mimicry, nonlinear optics, and catalysis. Recently, we have focused on the porphycene using as the semiconducting materials for organic solar cell (OSC). OSC materials require for the absorption covering the visible to NIR regions and appropriate HOMO and LUMO energy levels. In this presentation, we have designed, synthesized and properties of the porphycene–diketopyrropyrrole conjugate (Pc–DPP) though ethynyl linkages for the OSC as p-type materials. The absorption of the DPP unit appears at around 450-550 nm, while porphycene has an absorption valley around 400-550 nm. The combination of DPP and porphycene via ethynyl linkages is expected to generate absorption covering the visible to NIR regions of the spectrum. We have measured absorption spectra of Pc–­DPP and 2,7,12,17-tetrahexylporphycene (THPc) as reference compound in thin-film on glass substrate. THPc has strong Soret band at 400 nm and Q-bands around 550 to 700 nm. On the other hand, as the result of the connection with porphycene and DPP units, Pc–DPP has broad absorption covering the visible to near in-fared regions. Based on these optical characters, we have fabricated bulk heterojunction (BHJ) OSC by solution process with Pc–DPP as a p-type material and PC61BM as an n-type material. The active layer of the mixture of Pc–DPP and PC61BM with 0.1% 1,8-diiodooctane containing chloroform was deposited on the PEDOT:PSS-treated ITO substrate by spin coating and then calcium and aluminum electrode were deposited on the active layer by vacuum process. After optimized the device conditions, we achieved the PCEs of 1.4% (J sc = 4.88 mA cm-2, V oc = 0.81 V and FF = 0.37). We will also report the evaluations of film structures of these devices by AFM and XRD measurements.

A prospective DFT study for assembling highly reactive clusters based on lithium boranes and alanates

In this work, first-principles calculations using the density functional theory are performed to study the structure, stability and electronic properties of lithium borohydrides (boranes) and lithium aluminohydrides (alanates). With the attachment of BH4 and AlH4 complexes to the Li atom, the electron affinity increases to 5.22 eV and 4.34 eV, in the clusters Li(BH4)2 and Li(AlH4)2, respectively, which indicate superhalogen behaviour. For the alanates, by decorating the Li atom with the superhalogen moiety, the electron affinity increases to 4.64 eV, in the large-sized cluster Li[Li(AlH4)2]2. The substitution of Al for B leads to larger NBO charges on the H atoms, as a result of the electron- donating character of the Al atom. The results show that, besides larger gravimetrical storage capacities, the boranes also have higher electron affinities than the alanates in the large-sized clusters. The significant HOMO-LUMO differences indicate that the new moieties, which are highly reactive, are chemically very stable species.

Modeling vacancies and hydrogen impurities in graphene: A molecular point of view

We have followed a ‘molecular’ approach to study impurity effects in graphene. This is thought as the limiting case of an infinitely large cluster of benzene rings. Therefore, we study several carbon clusters, with increasing size, from phenalene, including three benzene rings, up to coronene 61, with 61 benzene rings. The impurities considered were a chemisorbed H atom, a vacancy, and a substitutional proton. We performed HF and UHF calculations using the STO-3G basis set. With increasing cluster size in the absence of impurities, we find a decreasing energy gap, here defined as the HOMO–LUMO difference. In the case of H chemisorption or a vacancy, the gap does not decrease appreciably, whereas it is substantially reduced in the case of a substitutional proton. The presence of an impurity invariably induces an increase of the density of states near the HOMO level. We find a zero mode only in the case of a substitutional proton. In agreement with experiments, we find that both the chemisorbed H, the substitutional proton, and the C atom near a vacancy acquire a magnetic moment. The relevance of graphene clusters for the design of novel electronic devices is also discussed.

TD-DFT Description of Photoabsorption and Electron Transfer in a Covalently Bonded Porphyrin−Fullerene Dyad

Structure, photoabsorption, and excited states of a covalently bonded porphyrin-fullerene dyad H(2)P-O34-C(60) are studied using DFT and TD-DFT approaches. Charge transfer from the donor (porphyrin) to the acceptor (fullerene) and the excited-state geometrical relaxation are of special interest. An analysis of differences in the description of these delicate phenomena due to the different exchange-correlation functionals is presented. We compare the results given by LDA, GGA, and hybrid functionals (i.e., SVWN, PBE, B3LYP, and PBE0). The ground-state center-to-center (cc) equilibrium distance between the donor and the acceptor moieties is 6.3, 7.1, and 7.9 Angstrom with SVWN, PBE, and B3LYP, respectively. The associated charge transfer of 0.15, 0.11, and 0.09 electrons is shown to depend on this distance but not directly on the functional itself. The same trend is seen in the HOMO-LUMO difference results, and further, in the lowest excitation energies, except for the hybrid functional calculations that yield the largest HOMO-LUMO gap and the highest energy for the lowest electronic excitation. The hybrid functionals were not found practical for excited-state conformational relaxation with the present computing resources. With LDA, the relaxation increases the cc distance by about 0.2 Angstrom, which is associated with a 0.14 eV decrease in energy. As compared to the ground-state dipole moment of about 4 D, the relaxed excited-state charge-transfer complex dipole moment turns out to become about 20 D. A local excitation of the porphyrin donor is considered, as well, and based on all these results, the nature and interpretation of the photoinduced electron-transfer process is discussed.

Synthesis and Isolation of Chloro‐β‐carbolines Obtained by Chlorination of β‐Carboline Alkaloids in Solution and in Solid State.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and isolation of chloro‐β‐carbolines obtained by chlorination of β‐carboline alkaloids in solution and in solid state

Abstractβ‐Carbolines (1‐5) undergo electrophilic aromatic substitution with N‐chlorosuccinimide and N‐chlorobenzotriazole under different experimental conditions. Although 6‐chloro and 8‐chloro‐nor‐har‐mane (1a and 1b) and 6‐chloro and 8‐chloro‐harmane (2a and 2b) obtained by chlorination with sodium hypochlorite of nor‐harmane (1) and harmane (2) were isolated and fully characterized recently, other chloroderivatives of nor‐harmane and harmane have never been described. The preparation and subsequent isolation, purification and full characterization of the dichloroderivatives 1c and 2c are reported (mp, Rf, 1H nmr, 13C nmr and ms) together with the preparation, isolation and charaterization, for the first time, of the chloroderivatives obtained from harmine (3a‐3c), harmol (4a‐4b) and 7‐acetylharmol (5a‐5c). As chlorinating reagent N‐chlorosuccinimide and N‐chlorobenzotriazole in solution as well as the β‐carboline ‐N‐chlorosuccinimide solid mixture have been used and their uses have been compared. Gc (tR) and gc‐ms (m/z) data for other monochloro derivative of nor‐harmane (1d) and monochloro‐ and dichloroderivatives of harmane (2d and 2e‐2f), obtained in trace amounts, are also included (Scheme 1 and Table I). Semiempirical AM1 and PM3 calculations have been performed in order to predict reactivity in terms of the energies of HOMO‐LUMO difference and in terms of the charge density of β‐carbolines (1‐5) and chloro‐β‐carbolines (1a‐1c, 2a‐2c, 3a‐3c, 4a‐4b, and 5a‐5c) (Scheme 1). Theoretical and experimental results are discussed briefly.

Synthesis, structural and spectroscopic study of the donor–acceptor complexes between fluorene and D2hcyano molecular building blocks

Three solid molecular complexes of fluorene with electron-withdrawing tetracyanoethylene, 1,2,4,5-tetracyanobenzene and 7,7,8,8-tetracyanoquinodimethane were synthesized. Single-crystal X-ray diffraction data elucidated the order–disorder aspects of the crystal structures ascribed to the different molecular symmetries of the employed building blocks. This hypothesis was confirmed by the structural and energetic results of ab initio periodic calculations. Donor–acceptor solid state interactions between molecular counterparts have been highlighted by electron and vibrational IR and Raman solid state spectroscopy, indicating a significant extent of electron density transfer from the fluorene unit towards the cyano-molecules. The experimental evidences of donor–acceptor interactions between molecular counterparts were compared to the lattice energies and solid state band-gaps, obtained by periodic calculations, and to the cluster HOMO–LUMO differences, obtained by isolated cluster calculations. A good agreement between spectral and theoretical data was found.

Varying the fraction of orbital exchange in density functional theory: Influence on nuclear magnetic resonance shielding constants

A series of hybrid exchange-correlation functionals containing varying fractions of orbital exchange ξ=0.0, 0.1, 0.2, … 1.0, are determined using conventional molecular thermochemical fits. The functionals are used to determine Kohn–Sham nuclear magnetic resonance shielding tensors for a series of small molecules involving first- and second-row atoms; results are compared with experimental values. On average, isotropic and anisotropic shieldings determined using the conventional coupled approach become progressively less accurate as ξ increases from 0.0 to 1.0. By contrast, isotropic and anisotropic shieldings determined from the hybrid Kohn–Sham densities using the uncoupled multiplicative Kohn–Sham (MKS) approach [Chem. Phys. Lett. 337, 341 (2001)] improve significantly as ξ increases from 0.0 to 0.2–0.3; optimal results are more than three times as accurate as the corresponding coupled results. As ξ is further increased, the MKS results degrade. The quality of the Kohn–Sham highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) eigenvalue difference in the MKS calculations is investigated by comparing it with values determined from coupled cluster Brueckner doubles densities. In line with the shielding observations, optimal HOMO–LUMO differences are obtained near ξ=0.3.

Eigenvalues, integer discontinuities and NMR shielding constants in Kohn—Sham theory

Kohn—Sham eigenvalues are determined from coupled cluster electron densities. The calculated HOMO—LUMO eigenvalue differences are compared with those from conventional generalized gradient approximation (GGA) exchange-correlation functionals for a range of small molecules. In all cases, GGA HOMO—LUMO differences are smaller than those calculated from the coupled cluster densities. When the GGA HOMO—LUMO differences are explicitly corrected—such that they equal those calculated from electron densities—significant improvements in NMR shielding constants are obtained. The eigenvalues calculated from electron densities are also used to approximate the magnitude of the integer discontinuity in the exact exchange-correlation potential. The value of the Kohn—Sham HOMO eigenvalue is then considered. Although HOMO eigenvalues from high quality, asymptotically vanishing, exchange-correlation potentials are close to the negative of the ionization potential, HOMO eigenvalues from the GGA functionals are shifted upwards by approximately 50% of the calculated integer discontinuity. An alternative approach for correcting NMR shielding constants is investigated.

Solid state nuclear bromination with N-bromosuccinimide. Part 2. Experimental and theoretical studies of reactions with some substituted benzaldehydes †

N-Bromosuccinimide reacts with aromatic aldehydes in the solid state to yield exclusively nuclear brominated products while a similar reaction in the solution phase produces a number of products under varied conditions. The reactivity and regioselectivity have been studied in terms of the energies of HOMO, HOMO–LUMO difference, reaction free energy, reaction conditions and crystal packing. Single crystal X-ray structural analysis of 3,4-dihydroxybenzaldehyde has been carried out. Crystal packing energies of some of the reactive and unreactive benzaldehydes indicate the importance of molecular bromine diffusion in the solid state.

Stable Isomers of Sila - and Germadodecahedrane. a Semiempirical (Am1) Investigation of the Structure of 4/6 and 4/5/6 Ring Containing E20 (E=SI, GE) Systems

AMI molecular orbital calculations with full geometry optimisation of 4/6, 5/5 and 4/5/6 isomers of E20 (E=Si, Ge) show a clear preference of germanium to be accommodated in four membered rings and to achieve coordination numbers greater than 3 (V A). as a consequence, unlike C20 or Si20, the dodecahedral form of Ge20 was not localised on the potential surface, instead an opened structure derived from an octagermaprismane (IV B) can be predicted. Notable kinetic stabilisation in the (SiR)20 systems is suggested by the HOMO-LUMO differences.

Possible C20 Isomers Containing 4/6 Rings. As Ami Investigation of the Stability of Three 4/6 Cages and of Their Hydrogenated Analogues

Semiempirical AM1 calculations on isomers (I-III) of C20 constructed from six and four-membered rings reveal high enthalpies of formation compared to the dodecahedral or the planar cyclic isomers. Hydrogenation of I-III however reduces greatly their enthalpies of formation and increase the HOMO-LUMO differences making such species interesting targets for synthesis.

Absorption spectroscopy of (Ind)Ni(PPh3)X (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) and M(Ind)2 (M = Ni, Ru; Ind = indenyl)

The electronic structures of two types of transition metal indenyl complexes have been studied. The first type, a series of (Ind)Ni(PPh3)X compounds (Ind = indenyl, 1-Me-indenyl; X = Cl, Br, Me) was investigated by absorption spectroscopy and Extended Hückel Molecular Orbital calculations. The energy differences between calculated levels are in good agreement with experimental band positions. For example, the lowest energy singlet–singlet band maximum for (Ind)Ni(PPh3)Cl is at 19 500 cm−1 and the calculated HOMO–LUMO difference is 19 817 cm−1. For X = Me, the calculated energy difference increases to 21 930 cm−1 and the corresponding absorption band is at 22 500 cm−1. The influence of the metal–ligand interactions on the molecular orbitals is discussed. The second category of indenyls, the bis(indenyl) compounds of Ni and Ru, show absorption spectra that are markedly different from those of nickelocene and ruthenocene. For example, in comparison to nickelocene, the first absorption band of Ni(Ind)2 is 5700 cm−1 higher in energy and is more intense by two orders of magnitude; in contrast, the first absorption maximum of Ru(Ind)2 is 6600 cm−1 lower in energy than observed for ruthenocene. The characteristics and relaxation dynamics of the lowest energy excited states are discussed. Key words: absorption spectroscopy, indenyl, nickel, ruthenium, EHMO analysis.