Etude MNDO des composes conjugues enneagonaux

We present MNDO calculations of a series of nine-membered conjugated compounds. The geometries have been fully optimized. Cyclononatetraenyl and benzocyclononatetraenyl anions, nonapyrrol, and nonathiophene appear to be planar aromatic compounds. Following MNDO , nonafulvene has a planar prefered conformation, but a polyenic structure, while nonafuran and cyclononatetraene are gauche molecules. The Universal Huckel Method (UHM ), a simple all valence electron empirical technique which describes σ systems using localized MO , gives, qualitatively, the same results as the MNDO method. The quantum calculation carried out with MNDO and UHM have been used to describe the physicochemical properties of ninememberedring conjugated compounds under consideration. To our knowledge, we present here the first theoretical study dealing with nine-membered conjugated molecules.     

A comparative post-Hartree–Fock and density functional theory study of monochalcogenide diatomic molecules

HOMO and LUMO (FMOs) play important role in the optical properties of meridianal isomer of tris(8-hydroxyquinolino)aluminum (mer-Alq3) and its derivatives. The frontier molecular orbitals (FMOs) also play a vital role in the process of charge transport. It is urgent to find the reason of FMO distribution pattern among the ligands. The structures of mer-Alq3 and its “CH”/N substituted derivatives have been optimized at the B3LYP/6-31G^* level. Energy decomposition analysis has been performed at the B3LYP/DZP level. The results of energy-partitioning analysis of ground states are discussed. It has been explained that HOMOs are on A-ligands due to weaker electrostatic interaction energy between L_a-AlL_bL_c fragments while LUMOs are on B-ligands due to weaker orbital interaction energy between L_b-AlL_aL_c fragments.     

Theoretical study of selenium and tellurium impurities in (ZnO)6 clusters using DFT and TDDFT

Zinc oxide (ZnO) nanostructures have attracted much interest due to their potential applications in various fields including optoelectronics, glass industries, and solar cells. These compounds hold the promise of creating new materials that can advance energy technologies. In this work, a series of (ZnO)₆ clusters with selenium and tellurium applied as substitutional impurities has been studied. The investigated structures have been produced through the doping of (ZnO)₆ clusters by replacing an oxygen atom with a selenium or a tellurium atom at each time. The ground state geometric parameters of (ZnO)₆ structures, containing selenium or tellurium atoms as substitutional impurities, were calculated using density functional theory (DFT) with B3LYP and LanL2DZ basis set. Excited state energies and absorption wavelengths were computed using time‐dependent‐DFT (TDDFT). For the calculation of emission wavelengths, Hartree–Fock configuration interaction singles (HF/CIS) has been used in order to perform the excited state geometry optimization. This work led to some important results that can be helpful for developing novel THz sensitive materials and imaging detectors that may be an alternative to x‐rays detectors for radiology as well as for the development of solar cells and electroluminescent diodes. Zinc oxide (ZnO) nanostructures have attracted growing interest due to their potential applications in many technological fields, including optoelectronics, the glass industry, and energy. The presence of impurities, in particular selenium and tellurium, in ZnO‐based clusters can affect their structural and spectroscopic properties. Some of these doped nanostructures have favorable Terahertz emission characteristics that make them good candidates for applications in biology and medicine.     

Prototropic tautomerism and microsolvation in antitumor drug imexon: a DFT study

Density functional theory method, at the B3LYP/6–311+G(d, p) level has been used to explore the geometries, relative energies, and electronic properties of all hypothetically possible prototropic tautomers of imexon. The specific interactions of the tautomeric forms of imexon with one and two solvating water molecules have been investigated. The relative stability order of the complexes remains unchanged upon interaction with one water molecule. The addition of a second water molecule, however, stabilizes the oxo-amino form more than the oxo-imino structure. The bulk water environment has been simulated by a combination of microhydration and the conductor-like polarizable continuum model. The energy profile corresponding to the prototopic tautomerisms connecting oxo-imino form with oxo-amino, hydroxyl-amino, and one rare tautomer has been studied. We found that the tautomerism activation barriers are high enough as to conclude that only the oxo-imino tautomer should be found in the gas phase. Our results present clear evidence that microhydration with one and two solvating water molecules considerably lower these barriers by a concerted multiple proton transfer mechanism.

     

Study of the Influence of the Nature and Position of the Halogen Atom in the N-Halogenophenyl-2,5-dimethylpyrrole Upon the Vibrational (Hyper)polarizability: Theoretical Study

The two contributions, vibrational and electronic, to the electrical properties polarizability and first hyperpolarizability of the N-[(2, 3, or 4)-fluorophenyl]-2,5-dimethylpyrrole are evaluated theoretically at the HF/6-31G level within the double harmonic oscillator approximation. The calculations demonstrate that, with the exception of the second harmonic generation, the vibrational contribution to the first hyperpolarizability is important. However, the vibrational polarizability, contributes at most, 10% to the total electric polarizability. The analysis upon the sum-over-states expressions shows that there are only few modes which contribute strongly and, generally, have small vibrational energies. The effect of the fluorine substitution by an other substituent is also addressed.     

Theoretical analysis of the electronic properties of N3 derivatives

The structural and electronic properties of nine derivatives of the N3 complex (cis-[Ru(4,4'-COOH-2,2'-bpy)2(NCS)2]) have been studied, using density functional theory (DFT) at a hybrid (PBE0) level, with the aim of finding a systematic way to improve their spectral absorption in the visible region for photoelectrochemical applications. To this end, by means of time dependent-DFT (TD-DFT) calculations, excited states were investigated in solution to simulate UV-vis spectra. Several effects have been taken into account: the effect of the presence and deprotonation of the carboxylic groups as well as the variation of the chalcogen within the NCX ligand (X=S, Se, or Te). Besides the excellent agreement between theoretical and available experimental data, with regards to potential future experimental applications of the investigated complexes, from the calculations, the cis-Ru(dcbpyH2)(NCSe)2 may appear as a good candidate to enhance the response of the N3 dye to light, even if only slightly.