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Internal Oriented Electric Fields as a Strategy for Selectively Modifying Photochemical Reactivity
摘要： Time dependent density functional theory calculations have been performed on acetophenone derivatives to explore the possibility of using charged functional groups as internal electric fields, the orientation of which can be altered to change photochemical behavior at will. Results demonstrate that non-conjugated charged groups can significantly alter, by up to -1.44 eV, the stabilities of excited states. Specifically, a non-conjugated negatively charged group in the para-position will destabilize the nπ* and stabilize the ππ* transitions, while a positively charged group will do the opposite. These electrostatic effects can be tuned by moving these substituents into the meta and ortho positions. Through use of acids and bases, these charged groups can switched on or off with pH, allowing for selective alteration of the energy levels and photochemical reactivity. Solvent effects are shown to attenuate the electric field effect with increasing dielectric permittivity; however electrostatic effects are shown remain significant even in quite polar solvents. Using charged functional groups to deliver the position-dependent electrostatic (de)stabilization effects is therefore a potential route to improving the efficiency of desirable photochemical processes.
关键词： electric fields,acetophenone derivatives,TD-DFT,excited states,photochemical reactivity
更新于2025-09-10 09:29:36
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Effects of nitrogen on the interface density of states distribution in 4H-SiC metal oxide semiconductor field effect transistors: Super-hyperfine interactions and near interface silicon vacancy energy levels
摘要： The performance of silicon carbide (SiC)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) is greatly enhanced by a post-oxidation anneal in NO. These anneals greatly improve effective channel mobilities and substantially decrease interface trap densities. In this work, we investigate the effect of NO anneals on the interface density of states through density functional theory (DFT) calculations and electrically detected magnetic resonance (EDMR) measurements. EDMR measurements on 4H-silicon carbide (4H-SiC) MOSFETs indicate that NO annealing substantially reduces the density of near interface SiC silicon vacancy centers: it results in a 30-fold reduction in the EDMR amplitude. The anneal also alters post-NO anneal resonance line shapes significantly. EDMR measurements exclusively sensitive to interface traps with near midgap energy levels have line shapes relatively unaffected by NO anneals, whereas the measurements sensitive to defects with energy levels more broadly distributed in the 4H-SiC bandgap are significantly altered by the anneals. Using DFT, we show that the observed change in EDMR linewidth and the correlation with energy levels can be explained by nitrogen atoms introduced by the NO annealing substituting into nearby carbon sites of silicon vacancy defects.
关键词： MOSFETs,silicon carbide,NO anneals,interface density of states,DFT,EDMR
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Estimation of the Power Quality Changing Parameters Using DFT Coefficients
摘要： In paper, algorithms for fast measurement and estimation of the changing frequency components parameters and other power parameters for evaluation of the power quality disturbances, are presented. Parameters are calculated from the largest local DFT coefficients of particular frequency components. The improvement for reducing the influences of the harmonic components is the estimation below or equal to one signal period.
关键词： interpolation,non-parametric estimation,windowing,power quantities,DFT coefficients
更新于2025-09-10 09:29:36
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NBO, nonlinear optical and thermodynamic properties of 10-Acetyl-10H-phenothiazine 5-oxide
摘要： In this paper, natural bond orbital (NBO) analysis, nonlinear optical and the thermodynamic properties of 10-Acetyl-10H-phenothiazine 5-oxide have been analyzed by employing density functional theory level employing 6-311++G(d,p) basis set. NBO analysis reveals that the intra- intermolecular charge transfer occurs within the molecule leading to the stabilization. The predicted nonlinear optical properties (NLO) like; polarizability and first hyperpolarizabiliy support that the molecule could attract the interests for future investigation.
关键词： DFT,Nonlinear optical and thermodynamic properties.,NBO,APTZ
更新于2025-09-10 09:29:36
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New Aryl-Substituted 2,2′-Bithiophenes: Synthesis, Optoelectronic Properties and DFT Studies
摘要： New Aryl-Substituted 2,2’-Bithiophenes: Synthesis, Optoelectronic Properties and DFT Studies. Toreshettahally R. Swaroop,[a, b] Zahra A. Tabasi,[b] Yuming Zhao,*[b] and Paris E. Georghiou*[b] and thien-2-yl-[2, 2’-bithiophen]-5-yl)(thiophen-2-yl) Phenyl- methanones were synthesized by the condensation of 2- thienyldithioester with the corresponding methyl ketones followed by cyclization with 2-bromoacetylthiophene. Also, condensation of 2-thienyldithioester with methyl ketones followed by treatment with methyl iodide gave β-thien-2-yl-β- methylthio-α,β-unsaturated ketones, which reacted with the Simmons-Smith reagent to give corresponding 4-phenyl- and thien-2-yl-2,2’-bithiophenes. The optoelectronic properties of these bithiophene derivatives were studied by UV-Vis absorption, fluorescence spectroscopy and cyclic voltammetry. The lowest-energy conformations of these new compounds in the ground and first excited states, the electronic origins of their UV-Vis absorption and fluorescence emission bands, and (FMO) properties were related frontier molecular orbital elucidated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Furthermore, these aryl-substituted bithiophenes were treated with anhydrous ferric chloride to undergo oxidative polymerization, and the fluorescence properties of the resulting polymeric products are also reported herein.
关键词： Thiophenes,UV-vis,Fluorescence,TD-DFT,Oligothiophenes
更新于2025-09-10 09:29:36
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Structural, optical and nonlinear optical properties and TD-DFT analysis of heteroleptic bis-cyclometalated iridium(III) complex containing 2-phenylpyridine and picolinate ligands
摘要： In this work, we studied the structural, optical and nonlinear optical properties and UV–visible absorption spectrum of the heteroleptic bis-cyclometalated iridium(III) complex (tfmppy)2Ir(pic) recently synthesized with tfmppy = 5-trifluoromethyl-2-phenylpyridine and pic = picolinate. The calculations were performed by means of density functional theory (DFT) and time-dependent density functional (TD-DFT) methods using four functionals B3LYP, PBE0, CAM-B3LYP and M06-2X. Calculated geometric parameters agree with the experimental data. CAM-B3LYP and M06-2X lower the HOMO energy level and give a large energy gaps compared with B3LYP and PBE0. The four functionals show that LUMO is delocalized over ??? ppy and dIr orbitals. The studied complex gets a remarkably large first-order NLO response. B3LYP would provide good estimates of the energy gap and shows the strongest values of the first hyperpolarizabilities βHRS; M06-2X and CAM-B3LYP functionals overestimate the gaps and lower βHRS values. PBE0 and B3LYP spectra agree better with the experimental spectrum in the visible region, while CAM-B3LYP and M06-2X are more accurate in UV-C region. Natural transition orbital analysis shows that the weak band observed at 468 nm corresponds to MLCT/LLCT charge transfer transitions and the intense band observed at 270 nm is mainly assigned to intra-ligand state.
关键词： Excited states,Wiberg indices,Absorption spectrum,Hyperpolarizability,Complexes,Iridium,NTO,TD-DFT,Optical, nonlinear optical,Picolinate
更新于2025-09-10 09:29:36
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Influence of Crystal Structure and 3d Impurities on the Electronic Structure of the Topological Material Cd3As2
摘要： This paper presents a theoretical study of the effects of crystal structure and Mn and Co substitutions for Cd on the electronic structure of the topological material Cd3As2. We have carried out density functional theory calculations of the band structure and density of states in tetragonal and cubic Cd3As2, as well as in Cd3 – xMnxAs2 and Cd3 – xCoxAs2 crystals. The results indicate that the band structure of the cubic Cd3As2 phase differs significantly from that of a Dirac semimetal, characteristic of the tetragonal phase. It has also been shown that, after Co substitution for 1/24 of the Cd atoms, the structure of the density of 3d electron states is similar to that of the density of states in the magnetic semiconductor Cd3 – xMnxAs2, with a characteristic minimum at the Fermi energy. At the same time, in the case of analogous Mn substitution for Cd, the density of d-electron states has no such minimum.
关键词： Mn,density functional theory (DFT) calculations,magnetic semiconductors,topological materials,Co,Cd3As2,Dirac semimetal,band structure,density of states (DOS)
更新于2025-09-10 09:29:36
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Structures of the neutral and positively charged forms of the 4,4′,4″-tris(N,N-phenyl-3-methylphenylamino)triphenylamine (m-MTDATA) molecule and its dimer, and charge localization in the corresponding cationic species
摘要： The structures of the 4,4′,4″-tris(N,N-phenyl-3-methylphenylamino)triphenylamine (m-MTDATA) molecule and its dimer in their neutral and positively charged forms were studied by performing quantum-chemical calculations at the Hartree?Fock (HF) and density functional theory (DFT) levels of theory using several exchange-correlation functionals (PBE, PBE0, BHANDHLYP, and M06-HF) with different percentages of HF exchange. It was found that there are at least four possible isomeric structures of m-MTDATA with different (planar or perpendicular) arrangements of the peripheral diphenylamino groups. The charge localization in the monomeric and dimeric cationic species was also determined. The results indicated that the charge on the dimeric cation is localized on the central region or on the side fragment of the cationic part of the dimer, depending on the dimer structure. DFT calculations showed a tendency to overestimate the charge delocalization over the molecule, irrespective of the percentage of HF exchange applied.
关键词： QC calculations,DFT,Hartree?Fock,Charge localization,Dimer
更新于2025-09-10 09:29:36
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Effect of substituents on photophysical and aggregation behaviour in quinoline based bis-terpyridine Zn(II) complexes
摘要： Synthesis of the terpyridine based novel Zn(II) complexes (C1-C3) have been described. Characterization of these complexes has been achieved by spectroscopic studies (IR, 1H, 13C, 19F, HRMS, UV/Vis and fluorescence) and structure of C1 determined by X-ray single crystal analyses. Cautious tuning by incorporating appropriate substituents (–H; C1, –CH3; C2 and –OCH3; C3) enabled the complexes to exhibit solvent dependent emission indicative of more polarized excited state probably due to enhanced intramolecular charge transfer (ICT). Occurrence of aggregation induced emission (AIE) in C3 has been validated by solid state emission and vital role of RIR in inducing AIE upon aggregation by fluorescence lifetime experiments. The role of solvent and substituents on photophysical behaviour and morphology of the complexes has been investigated by UV/Vis, emission and scanning electron microscopy (SEM). As well, lowering of the energy gap between HOMO and LUMO by electron donating substituents –CH3 (C2) and –OCH3 (C3) has been supported by DFT studies.
关键词： Zn(II) complexes,photophysical properties,DFT studies,aggregation induced emission,terpyridine
更新于2025-09-10 09:29:36
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Modeling the Vibrational Properties of InSb Diamondoids and Nanocrystals Using Density Functional Theory
摘要： Raman and infrared spectra were used to obtain the vibrational properties of an indium antimonide crystal. The density functional theory of the Perdew, Burke and Ernzerhof functions/3-21G and the functions’ basis of polarization were employed. This study investigates how the vibrational frequencies of InSb diamondoids change with size as compared to the experimental bulk. The results showed that the bond lengths in InSb diamondoids decreased as the number of atoms within increased. Many physical properties were studied, including energy gaps, tetrahedral angles, dihedral angles, atomic charges, and bond lengths. The high reduced mass mode (HRMM) and high force constant mode were found to be larger in octamantane than in diamondoids, at 211.09 cm?1 and 190.17 cm?1, respectively.
关键词： PBE/3-21G,InSb diamondoids,DFT,Raman spectra,Infrared spectroscopy
更新于2025-09-10 09:29:36