Electronic Transition Strengths Research Articles

Synthesis, Quantum Computational Analysis and Molecular Docking of 3-(2-Hydroxyphenyl)-1-Phenyl Propanone: A Combined Experimental and Theoretical Analysis

The newly synthesized 3-(2-Hydroxyphenyl)-1-phenyl propenone was analyzed. In this work, optimization of the 3-(2-hydroxyphenyl)-1-phenyl propanone was carried out with DFT using B3LYP method utilizing 6-311++G(d,p) basis set. The structure parameters of the compounds as molecular geometry, bond lengths, bond angles, atomic charge, and HOMO-LUMO energy gap have been investigated and compound with the reported experimental results. The donor and acceptor interactions in 3-(2-Hydroxyphenyl)-1-phenyl propenone were investigated using natural bond orbital (NBO) analysis. By matching the obtained UV-Vis spectra to the time-dependent (TD)-DFT analysis, the energies of band gap, absorption wavelength, and oscillatory strength of 3-(2-Hydroxyphenyl)-1-phenyl propenone were found. Density of states for total (TDOS), partial (PDOS), and also overlap population (OPDOS) analysis were obtained. Molecular electrostatic potential (MEP) provides the information on the electrophilic, nucleophilic, and free radical prone reactive sites of the molecule. Non-linear optical features were demonstrated from the first-order hyperpolarizability. Based on the above results the 3-(2-Hydroxyphenyl)-1-phenyl propenone compound was investigated for further biological investigation. TD-DFT analysis was also performed to calculate energies, oscillator strength of electronic singlet-singlet transitions, and the absorption wavelengths. The Molecular docking (ligand-protein) simulations have been performed using the Auto Dock version 4.2.6.

Synthesis and spectroscopic characterization of nicotinaldehyde based derivatives: SC-XRD, linear and non-linear optical studies

In this study, new arylated derivatives of pyridine named as 6-(4-tertbutylphenyl)-nicotinaldehyde (TBPNA) and 6-(4-hydroxyphenyl)-nicotinaldehyde (HPNA) were synthesized by Suzuki Miyaura CC coupling approach. The structures of newly synthesized compounds were authenticated by spectroscopic techniques like FT-IR, UV-Vis, and 1H-NMR. Furthermore, the structural features of TBPNA and HPNA were explored by using the single-crystal X-ray diffraction technique (SC-XRD) showing monoclinic crystal structure and P21/c space group for both compounds. For a comprehensive study of the compounds, a computational quantum chemical study is also performed by using the density functional theory (DFT). The said compounds were optimized using the B3LYP method and a 6-311++G(d, p) basis set. The comparison of theoretical (DFT) and experimental (SC-XRD) data on structural parameters displayed good agreement. Frontier molecular orbital (FMO), natural bond orbital (NBO), the molecular electrostatic potential (MEP), and time-dependent density functional theory (TD-DFT) were also performed at the B3LYP/6-311++G(d,p) level of theory to get complete insights into electronic communications, intramolecular charge transfer (ICT) process, electronic transition and oscillation strength. The optoelectronic and non-linear optical (NLO) responses of the synthesized compounds were determined by computing the total dipole moment (μtot), average polarizability ⟨α⟩, and the first hyperpolarizability (βtot) at different functional(s) such as HF, M06, M062X, CAM-B3LYP, LC-BLYP, and B3LYP, paired with the 6-311++G(d,p) basis set. The B3LYP method exhibited the highest values of ⟨α⟩ and (βtot) for HPNA and TBPNA, which were found to be many times higher than the value of urea (⟨α⟩ = 34.055 a.u., βtot =90.527 a.u.), used as a standard NLO material.

Design, Synthesis, Spectroscopic Characterization, Molecular Docking and Biological Evaluation of 9H-Carbazole Linked 4-Nitrophenol: A DFT Approach

The FT-IR and FT-Raman spectra of 3-(4-nitrophenoxy)-9,9a-dihydro-4aH-carbazole (9HCNP) molecule were recorded. The theoretical wavenumbers are in proper agreement with the observed results. The electronic properties, such as natural bond orbital study of the molecule, were confirmed using the inter/intra molecular interactions, molecular electrostatic potential, and Mulliken population analyses on the atomic charge distribution, performed by the Becke-3–Lee–Yang–Parr (CAM-B3LYP) method utilizing Gaussian 09 software. The oscillator strength of electronic transitions and energies of HOMO and LUMO molecular orbitals were carried out to evaluate the global chemical reactivity descriptors of 9HCNP. The molecular docking evaluation was carried out to evaluate the structure–activity relationship and the binding affinity of the molecule, which shows that the molecule can perform as an inhibitor of breast cancer-causing human topoisomerase-I and II-DNA receptors. The result of the conjugation was found to play a significant role in bioactivity and drug-likeliness properties, which can be supported by the molecular docking analysis of those compounds. In addition, the morphological changes in control and in vitro cytotoxicity of 9HCNP confirm the anticancer activity of 9HCNP against human breast cancer cell lines was assessed in 24-h tetrazolium-dye (MTT) cytotoxicity assays and also analyzed in terms of the role of reactive oxygen species (ROS) in cell life. Hence, the results show the in vitro anticancer activity of the molecule for the development of human breast cancer drugs.

Time-resolved cathodoluminescence investigations of AlN:Ge/GaN nanowire structures

Light emitting diodes represent a key technology that can be found in many areas of everydays life. Therefore, the improvement of the efficiency of such structures offers a high economic and ecological potential. One approach is electrostatic screening of the quantum-confined Stark effect (QCSE) in polar III-V heterostructures by n-type doping in order to increase the oscillator strength of electronic transitions in quantum structures. In this study, we analyzed the cathodoluminescene (CL) spectra of different functional parts of individual AlN/GaN nanowire superlattices and studied their decay characteristics with sub-nanosecond time resolution. This allows us to extract information about strain and electric fields in such heterostructures with an overall spatial resolution <100 nm. The samples, which were investigated in a temperature range from 10 to 300 K by using time-integrated cathodoluminescence spectroscopy (TICL) and time-resolved cathodoluminescence spectroscopy (TRCL) consist of GaN bottom and top layer and a 40-fold stack of GaN nanodiscs, embedded in AlN barriers that were doped with Ge. We show, that the QCSE is reduced with increasing doping concentration due to a screening of the internal electric fields inside GaN nanodiscs, resulting in a reduction of the carrier lifetimes and a blue shift of the emitted light. Due to the small diameter of the electron excitation beam CL offers the possibility to individually analyze the different functional parts of the nanowires.

Efficient strain-induced light emission in lonsdaleite germanium

Lonsdaleite germanium has a direct band gap, but it is not an efficient light emitter due to the vanishing oscillator strength of electronic transitions at the fundamental gap. Transitions involving the second lowest conduction band are instead at least three orders of magnitude stronger. The inversion of the two lowest conduction bands would therefore make hexagonal germanium ideal for optoelectronic applications. In this work, we investigate the possibility to achieve this band inversion by applying strain. To this end we perform ab initio calculations of the electronic band structure and optical properties of strained hexagonal germanium, using density functional theory with the modified Becke-Johnson exchange-correlation functional and including spin-orbit interaction. We consider hydrostatic pressure, uniaxial strain along the hexagonal c axis, as well as biaxial strain in planes perpendicular to and containing the hexagonal c axis to simulate the effect of a substrate. We find that the conduction-band inversion, and therefore the transition from a pseudo-direct to a direct band gap, is attainable for moderate tensile uniaxial strain parallel to the lonsdaleite c axis.

Control of magnetic properties in spinel ZnFe2O4 thin films through intrinsic defect manipulation

We present a systematic study of the magnetic properties of ZnFe2O4 thin films fabricated by pulsed laser deposition at low and high oxygen partial pressure and annealed in oxygen and argon atmosphere, respectively. The as-grown films show strong magnetization, closely related to a non-equilibrium distribution of defects, namely, Fe cations among tetrahedral and octahedral lattice sites. While the concentration of tetrahedral Fe cations declines after argon treatment at 250 °C, the magnetic response is enhanced by the formation of oxygen vacancies, evident by the increase in near-infrared absorption due to the Fe2+–Fe3+ exchange. After annealing at temperatures above 300 °C, the weakened magnetic response is related to a decline in disorder with a partial recrystallization toward a less defective spinel configuration.

Quantum interference in second-harmonic generation from monolayer WSe2

A hallmark of wave-matter duality is the emergence of quantum-interference phenomena when an electronic transition follows different trajectories. Such interference results in asymmetric absorption lines such as Fano resonances, and gives rise to secondary effects like electromagnetically induced transparency (EIT) when multiple optical transitions are pumped. Few solid-state systems show quantum interference and EIT, with quantum-well intersubband transitions in the IR offering the most promising avenue to date to devices exploiting optical gain without inversion. Quantum interference is usually hampered by inhomogeneous broadening of electronic transitions, making it challenging to achieve in solids at visible wavelengths and elevated temperatures. However, disorder effects can be mitigated by raising the oscillator strength of atom-like electronic transitions - excitons - which arise in monolayers of transition-metal dichalcogenides (TMDCs). Quantum interference, probed by second-harmonic generation (SHG), emerges in monolayer WSe2, without a cavity, splitting the SHG spectrum. The splitting exhibits spectral anticrossing behaviour, and is related to the number of Rabi flops the strongly driven system undergoes. The SHG power-law exponent deviates strongly from the canonical value of 2, showing a Fano-like wavelength dependence which is retained at room temperature. The work opens opportunities in solid-state quantum-nonlinear optics for optical mixing, gain without inversion and quantum-information processing.

Quantum Chemical Study of the Solvent Effect on the Anticancer Active Molecule of Iproplatin: Structural, Electronic, and Spectroscopic Properties (IR, 1H NMR, UV)

The structural, electronic, and spectroscopic properties of the anticancer active molecule of iproplatin were investigated in the gas and liquid phases. Based on the polarizable continuum model (PCM), the solvent effect on the structural parameters, frontier orbitals, and spectroscopic parameters of the complex was investigated. The results indicate that the polarity of solvents plays a significant role in the structure and pro perties of the complex. 1H and 13C NMR chemical shifts were calculated using the Gauge-invariant atomic orbital (GIAO) method. Pt–Cl and Pt–OH bonds were investigated through a vibrational analysis. Moreover, time dependent density functional theory (TD-DFT) was used to calculate the energy, oscillatory strength, and wavelength absorption maximum (λmax) of electronic transitions and its nature within the complex.

Effects of crossed electric and magnetic fields on the interband optical absorption spectra of variably spaced semiconductor superlattices

The interband optical absorption spectra of a GaAs–Ga1−xAlxAs variably spaced semiconductor superlattice under crossed in-plane magnetic and growth-direction applied electric fields are theoretically investigated. The electronic structure, transition strengths and interband absorption coefficients are analyzed within the weak and strong magnetic-field regimes. A dramatic quenching of the absorption coefficient is observed, in the weak magnetic-field regime, as the applied electric field is increased, in good agreement with previous experimental measurements performed in a similar system under growth-direction applied electric fields. A decrease of the resonant tunneling in the superlattice is also theoretically obtained in the strong magnetic-field regime. Moreover, in this case, we found an interband absorption coefficient weakly dependent on the applied electric field. Present theoretical results suggest that an in-plane magnetic field may be used to tune the optical properties of variably spaced semiconductor superlattices, with possible future applications in solar cells and magneto-optical devices.

Substituent and solvent effects on geometric and electronic structure of C5H5Ir(PH3)3 iridabenzene: A theoretical insight

Using MPW1PW91 quantum chemical calculations, we report structures, frontier orbital analysis, natural bond analysis, and aromaticity of the C5H5Ir(PH3)3 iridabenzene and XC5H4Ir(PH3)3para-substituted iridabenzenes. The substituent effects were estimated from the donor–acceptor interaction energies of the natural bond orbitals of substituent and iridabenzene frame. Nucleus-independent chemical shift (NICS) has been evaluated to understand the aromaticity. Time dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λmax) of electronic transitions and their nature. Changes in hyperpolarizability of molecules are studied. Influence of solvent on the structure, frontier orbital energies, λmax, and hyperpolarizability of C5H5Ir(PH3)3 iridabenzene has been studied.

UNDERSTANDING THE STRUCTURE, SUBSTITUENT EFFECT, NATURAL BOND ANALYSIS AND AROMATICITY OF OSMABENZYNE: A DFT STUDY

The structures and properties of osmabenzyne and para-substituted osmabenzynes (X=F, Cl, Br, Me, NH2, OH, NO2, CHO, COOH) have been explored using theoretical methods. Frontier orbital analysis indicates the HOMO and LUMO are distributed on the ring carbon atoms, Os and Cl ligands. Time dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λmax) of various electronic transitions and their nature within molecules. Non linear optical (NLO) behavior of title compounds is investigated by the computed value of first hyperpolarizability (βtotal).

Computational study of gas-phase molecular structure and substitution effects in para-substituted nickelabenzenes (p-XC5H4)Ni(CO)2F

The structure and properties of nickelabenzene complex were examined by the Modified Perdew-Wang Exchange and Correlation method (mpw1pw91). The para-substitutions effect on the structure, frontier orbital energies, aromaticity and electronic spectra has been studied. Nucleus independent chemical shift (NICS) values show that these species are aromatic. Time dependent density functional theory (TD-DFT) was used to calculate the energy, oscillator strength and absorption maxima wavelength (λmax) of various electronic transitions and their nature within molecules.

MOLECULAR STRUCTURE, NATURAL BOND ORBITAL, SUBSTITUENT EFFECT AND CHEMICAL REACTIVITY ANALYSIS OF TERMINAL BORYLENE RUTHENIUM COMPLEXES: Ru(PH3)2HCl(BC6H4X)

The structure and properties of a terminal borylene ruthenium complexes Ru ( PH 3)2 HCl ( BC 6 H 4X) have been investigated using theoretical methods. Frontier orbital analysis indicates the HOMO is distributed on the Ru and Cl ligand. On the other hand, LUMO is distributed on the Ru and phenyl ligand. The influence of solvent on the structure and properties of X = H structure has been studied. Time-dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λmax) of various electronic transitions and their nature within molecules. Nonlinear optical (NLO) behavior of title compounds is investigated by the computed value of first hyperpolarizability (βtotal).

Effects of dynamic disorder on exciton delocalization and photoinduced charge separation in DNA

The nature of electronically excited states in DNA is analyzed in detail using a combination of quantum mechanical (QM) semiempirical calculations and molecular dynamics (MD). For this purpose, we consider homogeneous π stacks extracted from the MD trajectory of a poly(A)·poly(T) oligomer. The environment is accounted for within the QM/MM scheme. The effects of structural fluctuations on exciton delocalization and photoinduced charge separation are explored using the quantitative analysis of the electron density in the excited states. We distinguish the effects generated by the vibronic interactions within nucleobases and by the environment of the π stack. While in ideal B-DNA stacks (A-T)n singlet excited states are spread over all intrastrand nucleobases, the average exciton length is ~0.75n, thermal fluctuations decrease considerably the extent of delocalization. The QM/MD model predicts that the excitons in (A-T)n stacks are spread over 3 bases (for n = 4 and 6, the average exciton length is found to be 2.6 ± 0.3 and 2.8 ± 0.3, respectively). We show that the main factor reducing the exciton length is the vibronic interactions within nucleobases whereas fluctuations of the π stack environment play a relatively minor role. The oscillator strength of electronic transitions from the ground state to charge-separated states Ak(+)Ak±1(-) and Tk(+)Tk±1(-) is found to be strong enough to populate directly these states by UV absorption at E = 5.0-5.3 eV. In contrast, the direct formation of interstrand charge transfer states Ai(+)Tj(-) is predicted to be unlikely.

A combined experimental and theoretical (DFT and AIM) studies on synthesis, molecular structure, spectroscopic properties and multiple interactions analysis in a novel Ethyl-4-[2-(thiocarbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate and its dimer

In the present work, ethyl-4-[2-(thiocarbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate (3) has been synthesized and characterized by 1H NMR, UV–Vis, FT-IR and Mass spectroscopy. The formation of the compound and its properties have also been evaluated by quantum chemical calculations using DFT, B3LYP functional and 6-31G(d,p) as basis set. The calculated thermodynamic parameters show that the formation of 3 is an exothermic and spontaneous reaction at room temperature. 1H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO-d6 as solvent. Time dependent density functional theory (TD-DFT) is used to calculate the energy (E), oscillator strength (f) and wavelength absorption maxima (λmax) of various electronic transitions and their nature within the molecule. NBO analysis is carried out to investigate the charge transfer or charge delocalization in various intra- and intermolecular interactions of molecular system. The vibrational analysis indicates the formation of dimer in the solid state by intermolecular heteronuclear hydrogen bonding (NH⋯O). Topological parameters at bond critical points (BCP) are calculated to analyze the strength and nature of various types of intra and intermolecular interactions in dimer by Bader’s ‘Atoms in molecules’ AIM theory in detail. The binding energy of intermolecular multiple interactions is calculated to be 15.54kcal/mol, using AIM calculation. The local reactivity descriptors such as Fukui functions (fk+,fk-), local softnesses (sk+,sk-) and electrophilicity indices (ωk+,ωk-) analyses are performed to determine the reactive sites within molecule.

Synthesis, molecular structure, multiple interactions and chemical reactivity analysis of a novel ethyl 2-cyano-3-[5-(hydrazinooxalyl–hydrazonomethyl)-1H-pyrrol-2-yl]-acrylate and its dimer: A combined experimental and theoretical (DFT and QTAIM) approach

A detailed spectroscopic analyses of a newly synthesized ethyl 2-cyano-3-[5-(hydrazinooxalyl–hydrazonomethyl)-1H-pyrrol-2-yl]-acrylate (3) have been carried out using 1H and 13C NMR, UV–Visible, FT-IR and mass spectroscopic techniques. All the quantum chemical calculations have been carried out using DFT level of theory, B3LYP functional and 6-31G(d,p) as basis set. The 1H and 13C NMR chemical shifts are calculated using gauge including atomic orbitals (GIAOs) approach in DMSO-d6. TD-DFT is used to calculate the energy (E), oscillatory strength (f) and wavelength absorption maxima (λmax) of various electronic transitions and their nature within molecule. Natural bond orbital (NBO) analysis is carried out to investigate the various intra and intermolecular interactions in dimer and their corresponding second order stabilization energy (E(2)). A combined theoretical and experimental vibrational analysis confirms the existence of dimer and the binding energy of dimer is calculated as 9.21kcal/mol using DFT calculations. To determine the energy and nature of different interactions topological parameters at bond critical points (BCPs) have been analyzed by Bader’s ‘atoms in molecules’ (AIMs) theory in detail. Electrophilic charge transfer (ECT) is calculated to investigate the relative electrophilic or nucleophilic behavior of reactant molecules involved in chemical reaction. Global electrophilicity index (ω=5.5836eV) shows that title molecule (3) is a strong electrophile. The local reactivity descriptors such as Fukui functions (fk+,fk-), local softness (sk+,sk-) and electrophilicity indices (ωk+,ωk-) analyses are performed to determine the reactive sites within molecule.

A combined experimental and quantum chemical (DFT and AIM) study on molecular structure, spectroscopic properties, NBO and multiple interaction analysis in a novel ethyl 4-[2-(carbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate and its dimer

In the present paper, a new ethyl 4-[2-(carbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate (3) has been synthesized and characterized by 1H NMR, UV–Visible, FT-IR and Mass spectroscopy. The formation of the compound and its properties have also been evaluated by quantum chemical calculations using density functional theory (DFT), B3LYP functional and 6-31G(d,p) as basis set. The calculated thermodynamic parameters show that the formation of (3) is an exothermic and spontaneous reaction at room temperature. 1H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO-d6 as solvent. Time dependent density functional theory (TD-DFT) is used to calculate the energy (E), oscillator strength (f) and wavelength absorption maxima (λmax) of various electronic transitions and their nature within the molecule. NBO analysis is carried out to investigate the stabilization energy of various intra and intermolecular interactions in molecular system. The vibrational analysis indicates the formation of dimer in the solid state by intermolecular heteronuclear hydrogen bonding (NH⋯O) and the binding energy of dimer is calculated to be 10.40kcal/mol, using DFT calculations. Topological parameters at bond critical points (BCP) are calculated to analyze the strength and nature of various types of intra and intermolecular interactions in dimer by Bader’s ‘Atoms in molecules’ AIM theory in detail. The local reactivity descriptors such as Fukui functions (fk+,fk-), local softnesses (sk+,sk-) and electrophilicity indices (ωk+,ωk-) analyses are performed to determine the reactive sites within molecule.

Gamma-ray irradiation induced structural and optical constants changes of thermally evaporated neutral red thin films

Neutral red (NR) is polycrystalline in powder form, it transforms to nanocrystallite phase upon thermal deposition. Gamma-ray irradiation with doses 1.25–6 KGy induced partial transformation of nanocrystallite phase to amorphous structure. The changes of optical constants with γ-ray doses were calculated using spectrophotometer measurements of transmittance and reflectance at normal incidence of light over spectral range 200–2500 nm. The complex refractive index of NR film is highly influenced by exposure to γ-ray irradiation, the onset and optical energy gaps decrease with increasing γ-ray doses, and Urbach tail increases linearly with increasing irradiation dose. The type of electronic transition, oscillator, and electric dipole strengths and dispersion parameters were determined before and after irradiation. The spectral behavior of dielectric constant with γ-ray doses was also estimated.

Intensity analysis of overlapped discrete and continuous absorption by spectral simulation: The electronic transition moment for the B–X system in I2

The spectrum of I(2) is examined anew in the wavelength region 520-640 nm, where discrete absorption in the B-X transition is prominent. The spectrum is recorded with high quantitative precision at moderate resolution (0.1 nm) and is analyzed by least-squares spectral simulation, yielding the B-X electronic transition strength ∣μ(e)∣(2) with unprecedented precision (<2% relative standard error) over most of the studied region. The analysis also yields directly new estimates of the continuous absorption in this region, which support previous assessments of the A ← X transition but lower the C((1)Π(u)) ← X transition strength by 25%. The new analysis method is applicable to any situation where the discrete spectrum can be simulated reliably.

Band-mixing and strain effects in InAs/GaAs quantum rings

We analyze for the first time the coupled influence of band mixing, strain, and piezoelectricity on electronic structure, eigenstates, and optical transition strengths for InAs/GaAs quantum-ring structures. It is shown that band mixing and strain alter the level energies and optical absorption coefficients significantly.