جستجوی مقالات مرتبط با کلیدواژه « Oscillator strength » در نشریات گروه « شیمی »

The dipole moments and polarizabilities in various excited states of o-, m- and p-nitroanilines were estimated using Linder’s variant of Abe solvatochromic model. The ground and excited state dipole moments of these molecules were computed from experimental and theoretical studies using solvatochromic technique and Density Functional Theory (DFT) respectively. The trend observed for the various excited states dipole moments of the o-, m- and p- isomers of nitroaniline follow the order ortho>meta>para.  The excited state polarizabilities obtained for the electronic transitions in each of the compounds are reflective of the oscillator strength f values for these transitions.  Also, the excited singlet-state dipole moments obtained were higher than the calculated ground state dipole moments which shows that the excited singlet-state is more polar than the ground state for all the compounds studied. The effects of solvent manifest in form of enhancement to the electronic intensities. The results of the present analysis show internal consistency and agree reasonably with Abe’s theory.

The effect of substitution on some biologically active di- and tri-coumarins substituted 4-phenyl coumarins was investigated using absorption and fluorescence spectrum profiles. These studies helped in the estimation of excited-state dipole moments (μe) of coumarins by applying two renowned Solvatochromic shift methods Kawaski et al. and Ravi et al. Computational methodology was applied to find the ground state dipole moments (μg) and Onsager cavity of the coumarins from the optimized geometry of the molecules using DFT/B3LYP/6-31++ G(d,p) level of theory. The Mulliken charges, frontier molecular orbitals (FMO), and electrostatic potential surfaces (EPS) were theoretically generated utilizing their optimized geometries to validate the experimental findings. Time Dependent Density Functional Theory (TD-DFT) approach was applied to approximate the excitation energy, dispersion energy, cavitation energy, corresponding wavelengths, oscillator strength for different coumarins in gaseous phase in addition to benzene, ethanol and most polar aqueous medium. The large stoke’s shifts, and high μe values indicate that the intramolecular charge transfer (ICT) process occur in these coumarins which has coerced by an intense S0 → S1 electronic transition. The computational results were matched with the experimental analysis, and revealed characteristics electrical properties of coumarins, as well as confirming the presence of ICT in these coumarins.

The dipole moments and polarizabilities in various excited states of o-, m- and p-nitroanilines were estimated using Linder’s variant of Abe solvatochromic model. The ground and excited state dipole moments of these molecules were computed from experimental and theoretical studies using solvatochromic technique and Density Functional Theory (DFT) respectively. The trend observed for the various excited states dipole moments of the o-, m- and p- isomers of nitroaniline follow the order ortho>meta>para. The excited state polarizabilities obtained for the electronic transitions in each of the compounds are reflective of the oscillator strength f values for these transitions. Also, the excited singlet-state dipole moments obtained were higher than the calculated ground state dipole moments which shows that the excited singlet-state is more polar than the ground state for all the compounds studied. The effects of solvent manifest in form of enhancement to the electronic intensities. The results of the present analysis show internal consistency and agree reasonably with Abe’s theory.

Despite several studies towards anti-HIV therapy, HIV infections remain a challenge due to the resistivity of developed drugs. The emergence of new HIV-1 PR mutations has led to the drug resistance of the available FDA-approved drugs and lower activity towards the HIV protease. Based on this the molecular properties of 4-hydroxy-6-methyl-3-[(1E)-1-(2-phenylhydrazinylidene) ethyl]-2H-pyran-2-one (DHAA-PH) has been carried out using the hybrid Density Functional Theory (DFT) and Time-Dependent (TDFT) method at B3LYP/6-31+G(d,p) levels of theory. To substantiate the sensitivity of functional applied M06-2X/ 6-311++G(2d,2p) and mPWB1W/6-311++G(2d,2p) was used to calculate the geometric, IR, 1H NMR, and energy gap calculations.DFT calculations with M06-2X and mPWB1W were observed to agree with the experiment compared to B3LYP functional. The absorption spectra of DHAA-PH showed three distinct bands which were designated as S0 to S1, S0to S2, and S0 to S3 in order of increasing energy. The high intensity (oscillator strength) of S0 to S1 infers that the transition is quantum-mechanically allowed, while the low intensity of S0 to S2 and S0 to S3 transitions suggests quantum mechanically forbidden transitions. Molecular dynamics simulations revealed that the obtained MMGBSA binding energies are better compared to the experimentally reported binding energies for HIV-1 protease inhibitors. 3D QSAR and computational ADMET study were performed. Pharmacophore fragments of the compound were identified as well as the fragments determining its toxicity and metabolic properties. Based on the analysis of these fragments, the ways to further design promising HIV1-protease inhibitors were proposed.

ABSTRACT The application of many hetero-aromatic compounds in pharmaceutical and dye industries make the theoretical study of their dipole moment (µ) oscillator strength (f) and other photo-physical properties worthwhile. These properties determine the solubility of many compounds; predict the relationship between their structures, properties and performance. The f, µ, α, transition dipole moment (∆µ), vertical Excitation Energies (EE) and the frontier orbitals energy gap (ΔELUMO-HOMO) of the optimized structures of 3, 4-diphenylthiophene (DPT); 3, 4-dicarboxylic-2, 5-diphenylthiophene (DCDPT); and benzo[b] thiophene (BT) were determined in solvents of different polarity functions (∆P) by Time-Dependent Density Functional Theory, using Becke’s three parameter with Lee-Yang-Parr modification and 6-31G* basis set theory (TD- DFT- B3LYP/6-31G*). The associated quantum chemical descriptors of ΔELUMO-HOMO such as: Ionization Potential (IP) and global hardness (ƞ) for the compounds were also determined with the same level of theory. The µ of the molecules increases with increasing ∆P, but highest for DCDPT. Bathochromic shifts associated with decreasing EE were recorded for the electronic transitions in DCDPT compare with those observed for DPT and BT. The IP and ƞ increased as ∆P increases, suggesting high stability of these compounds in polar solvents. The energy gaps, its associated parameters and positive ∆µ suggested strong activity of the molecules, with DCDPT being the highest. This is in reasonable agreement with the experimental results for the molecules particularly if the experimental uncertainties are considered. Key words: Polarizability; photo-physical; excitation energy; oscillator strength; Time Dependent-Density Functional Theory