Effect of chlorine and bromine on the nonlinear optical, electronic, optoelectronic and thermodynamic properties on the BEDT-TTF molecule : Ab initio and DFT calculations

In this study, the RHF and B3LYP methods with cc-pVDZ basis set have been used to investigate the non-linear optical (NLO), electronic, optoelectronic and thermodynamic properties of bis (ethylenedithio) tetrathiafulvalene and its chlorine and bromine derivatives. The results show that the undoped molecule denoted BEDT-TTF or ET (Eg =3.88 eV) and its derivatives are semi-conductors materials. However, one of them, Br4ET molecule doped with bromine, considerably improves its energy band gap Eg =2.88 eV is less than 3 eV, which makes more ineresting electronic properties. Some parameters such as dipole moment, average polarizability and first order hyperpolarizability have been calculated. In order to compare the results of molecules and with those of Urea, we have computed first molecular hyperpolarizability ꞵ, doped structures (ET chlorinated and brominated) find applications in telecommunication, in modern communication technology and data storage as NLO active materials. Moreover, the chemical potential, ionization potential, electron affinity, electronegativity, global hardness, softness, refractive index, dielectric constant, electric field and electric susceptibility have also been determined. The results show that there is a good electronic transfer within the doped molecules and could have potential applications as semiconductor components, photovoltaic and photonic devices. Finally thermodynamic properties have been also computed.

Vibrational Spectra, Electronic Structure and Properties of the Molecules Aspirin and Ibuprofen.

The FT-IR Vibrational spectra analysis, electronic structures and properties of the anti-inflammatory drugs Aspirin and Ibuprofen in gas and water and ethanol have been studied by using ab initio and DFT computational calculation. The present investigation deals with the analysis of structural and bonding features responsible for biological activities, stability of the molecules, average polarizability, anisotropy, energies and the IR vibrational spectra of the molecules. The observed and the calculated vibrational frequencies are found to be in good agreement. The experimental FT-IR spectra also coincide satisfactorily with those of the theoretically constructed line spectra at the B3LYp/6-31+G* level of theory.

Thermotropic, refracting and thermo-optical properties in three homologs of 4-n-alkyl-4’-cyanobiphenyls

Investigations of temperature behaviour of the mean refractive index n, ordinary no and extraordinary ne refractive indices, and birefringence Δn have been carried out for three homologues of 4-n-alkyl-4’-cyanobiphenyls (n = 8, 10, 12). The principal polarizabilities α0 and αe, effective geometry parameter αeg and average polarizability αave have been calculated using the isotropic internal field model (Vuks approach). Temperature behaviour of the order parameter in regions of the smectic A–nematic, nematic–isotropic liquid and smectic A–isotropic liquid is discussed. All of the optical and orientational parameters, which have been obtained in this work, are in good agreement with the theoretical approach.

Correlation of structural and physico-chemical parameters with the bioactivity of alkylated derivatives of indole-3-acetic acid, a phytohormone (auxin)

As part of molecular recognition studies on the phytohormone indole-3-acetic acid (IAA) a series of alkylated IAAs has been examined. Phenyl-ring substitution (alkyl = methyl and ethyl) at positions 4-, 6- or 7- as well as pyrrole substitution at the 2- site resulted in the six compounds which are analyzed: 2-Me-IAA, 4-Me-IAA, 6-Me-IAA, 7-Me-IAA, 4-Et-IAA and 6-Et-IAA. The structure–activity relationships investigated include those between the geometrical parameters of the molecular structures determined by X-ray analysis, the growth-promoting activities in the Avena coleoptile straight-growth bioassay and relative lipophilicities calculated from retention times on a reversed-phase HPLC column and from R F values in reversed-phase TLC. Lipophilicities are correlated with the moments of inertia, average polarizability, molecular mass, and the van der Waals radii of the ring substituents. The influence of substitution on the electronic properties of the indole ring and its geometry is discussed on the basis of the UV and 1H NMR spectra.

Extreme infra-red dispersion of polar and non-polar liquids

The interaction between infra-red radiation and molecules in the liquid state reveals phenomena that are characteristic of (1) individual molecules, and (2) molecules only in the liquid state. To category (1) belong the spectral properties of molecules that are common to both the liquid and gaseous state—it is understood that there might be small shifts in the characteristic frequencies due to an interaction of the molecules in the liquid state. Most of the atomic vibration frequencies lie in the near infra-red but certain combination terms (made up of differences of near infra-red frequencies) are permitted in the spectral region considered. AIso some polyatomic molecules can have fundamental vibrational frequencies in the extreme infra-red. There is no evidence that pure rotation exists in liquids as in gases and this is understandable either by considering that shocks from neighbouring molecules are too disturbing for a free rotation to he maintained sufficiently long or, and this was experimentally verified for water, that the intermolecular fields are too powerful to permit free rotation for the quantum energies involved. This last explanation belongs to category (2) which implies a quasi-crystalline structure of liquids in which the molecules as a whole can oscillate linearly and execute oscillating rotational motions. Experimentally we can distinguish between phenomena that are characteristic of individual molecules (1) and those due to a quasi-crystalline structure, (2), by comparing the spectrum of a pure liquid with that of a solution where the intermolecular field is changed. The measurement of the absorption and reflexion of liquids not only reveals resonance phenomena; it permits the calculation of refraction and the molecular polarisation. The total molecular polarisation can be expressed as the sum of the electronic, atomic and permanent polarisation: P = P e + P a + P p = 4 π /3 N ( γ e + γ a + γ p ) = ε - 1/ε + 2 M/ d , (1) where N is the Avogadro number, γ the average polarizability, M the molecular weight, d the density and ε the static dielectric constant. This formula and those to follow neglect any interaction between molecules (except that the effective field acting is given by the Lorenz relation R = E + 4/3 P); however, we shall consider them as giving a first approximation for molecules in the liquid state.