Synthesis and properties of p-benzoquinone-fused hexadehydro[18]annulenes

A series of hexadehydro[18]annulenes fused with different numbers of p-benzoquinone, 4-6, were synthesized by stepwise transformation of the p-dimethoxybenzene moiety of the precursor dehydroannulene 3 fused with three 3,6-dimethoxy-4,5-dimethylbenzene units at 1,2-positions into p-benzoquinone using ceric ammonium nitrate. The UV-vis spectra of compounds 4 and 5, which have both electron-donating p-dimethoxybenzene unit(s) and electron-accepting p-benzoquinone unit(s) in the π-systems, showed the maximum absorption bands bathochromically shifted in comparison with 3 having only p-dimethoxybenzene units and 6 having only p-benzoquinone units. However, the solvatochromism expected for 4 and 5 was found to be quite weak possibly because the HOMO and LUMO (B3LYP/6-31G(d)) are not localized but rather delocalized over the whole π-systems.     

Optimisation of accurate rutile TiO<Subscript>2</Subscript> (110), (100), (101) and (001) surface models from periodic DFT calculations

In this paper, geometric bulk parameters, bulk moduli, energy gaps and relative stabilities of the TiO₂ anatase and rutile phases were determined from periodic DFT calculations. Then, for the rutile phase, structures, relaxations and surface energies of the (110), (100), (101) and (001) faces were computed. The calculated surface energies are consistent with the natural rutile powder composition, even if a dependence on the number of layers of the slab used to model the surface was identified. Internal constraints, consisting in freezing some internal layers of the slab to atomic bulk positions, were thus added to mimic the bulk hardness in order to stabilise the computed surface energies for thinner systems. In parallel, the influence of pseudopotentials was studied and it appears that four valence electrons for titanium atoms are sufficient. The aim of this study was to optimise accurate rutile TiO₂ surface models that will be used in further calculations to investigate water and uranyl ion sorption mechanisms.     

Co-adsorption NO and organic molecules on Cu sites in zeolites: Quantum chemical DFT calculations

The co-adsorption of organic molecules: acetone, formaldehyde, ethene and acetylene together with NO on the same Cu⁺ site in zeolite CuZSM-5 was investigated by DFT calculations. The aim of this study was to follow the effect of NO on activation of multiple bonds in organic molecules and the effect of organic molecules on the activation of NO bond. The extent of activation of CO, CC, CC as well as of NO bonds was characterized by the result of calculation as the elongation of the multiple bonds, decrease of bond order as the decrease of stretching frequency, while population analysis gave information on the mechanism of activation. It has been found that the presence of NO co-adsorbed on the same Cu⁺ site as organic molecule resulted in more effective activation of CO bond in acetone and formaldehyde, but resulted in a less effective activation of CC and CC bond in ethane and acetylene. On the other hand, the presence of organic molecule resulted in more effective activation of NO bond (more important bond weakening) in NO molecule. The most significant NO bond weakening took place if NO was co-adsorbed with acetone or formaldehyde. Both acetone and formaldehyde transmit the most negative charge to the Cu⁺-zeolite system if adsorbed “solo” in Cu-zeolite. This negative charge may be next transmitted to antibonding NO orbitals resulting in so important NO bond weakening.     

Vibrational spectroscopic study of poly(dimethylsiloxane)-ZnO nanocomposites

A series of poly(dimethylsiloxane)-zinc oxide (PDMS-ZnO) nanocomposites having different concentrations of ZnO nanoparticles (0, 1, 5, 10 and 20 wt%) have been prepared. Raman and FTIR-ATR spectroscopic analysis was performed in order to determine the interaction between the ZnO nanoparticles and PDMS polymer matrix. Density functional theory (DFT) using the (B3-LYP)/6-311++G(2df,2p) method was used to investigate the vibrational spectra of PDMS. A complete vibrational assignment is supported by the normal coordinate analysis, calculated Raman activities as well as IR intensities.The presence of ZnO nanoparticles in PDMS gives rise to significant differences in relative intensities of the characteristic vibrational bands with respect to the cross-linked polymer. The changes in relative intensities of Raman bands, as well as swelling measurements, were used to explain the effect of ZnO nanoparticles on the cross-linked structure of PDMS nanocomposites. It is established that ZnO nanoparticles influence the cross-linking density of the polymer matrix.     

The inhomogeneous electron liquid in some bioinorganic assemblies studied by density functional methods

The review starts with a discussion of some recent advances related to the foundations of density functional theory (DFT). Some emphasis is placed on methods which should have special relevance to bioinorganic assemblies. In particular, the inhomogeneous electron liquid in the ground state of such systems is a specific focal point. After a brief summary concerning the possible variational validity of some popular energy functionals, the future value of the important Dirac idempotent density matrix is emphasised, both from first principles and semiempirically by making use of X-ray diffraction experiments. The review concludes with two topical examples of bioinorganic assemblies. The first concerns our own work on an anticancer drug based on a Ru complex, while as a second example a recent DFT study of a molecular biosensor by K. Salazar-Salinas, L.A. Jauregui, C. Kubli-Garfias, J.M. Seminario [J. Chem. Phys. 130, 105101 (2009)] involving an Fe complex is briefly summarised.     

Anomalous electronic transport in quasicrystals and related complex metallic alloys

We analyse the transport properties in approximants of quasicrystals α-AlMnSi, 1/1-AlCuFe and for the complex metallic phase λ-AlMn. These phases present strong analogies in their local atomic structures and are related to existing quasicrystalline phases. Experimentally, they present unusual transport properties with low conductivities and a mix of metallic-like and insulating-like characteristics. We compute the band structure and the quantum diffusion in the perfect structure without disorder and introduce simple approximations that allow us to treat the effect of disorder. Our results demonstrate that the standard Bloch–Boltzmann theory is not applicable to these intermetallic phases. Indeed their dispersion relations are flat, indicating small band velocities, and corrections to quantum diffusion, which are not taken into account in the semi-classical Bloch–Boltzmann scheme, become dominant. We call this regime the small velocity regime. A simple relaxation time approximation to treat the effect of disorder allows us to reproduce the main experimental facts on conductivity qualitatively and even quantitatively.     

Study on structure and properties of transition metal doped BiF3 by first-principles

Structure and physical properties of BiF₃ doped with M=Cr, Cu, Fe, Mn, Ni, Ti, V and Co are calculated by the DFT+U method. Effect of metal doping on the electronic structure and optical response of host materials BiF₃ is investigated systematically. New energy levels are formed and located within the band gap, which could decrease the recombination rate of e⁻/h⁺ pairs. Furthermore, transition metal doping extends the optical absorption of BiF₃ to the visible spectral region.     

Effect of side by side interactions on the thermodynamic properties of adsorbed CO molecules on the Ni(111) surface: a cluster model study

The effect of electrostatic interactions on vibrational frequencies and thermodynamic properties of CO adsorbate on the Ni(111) surface is calculated by taking the first and second nearest-neighbour interactions into account. In order to obtain reasonable results, the cluster model of various surface adsorption sites with CO adsorbate is partially optimized, using Density Functional Theory and also the MP2 method for the hcp site. Comparison between DFT and MP2 results shows that DFT results are more reliable for this system. The stretching and bending frequencies of CO adsorbate are calculated using both Partial Hessian Analysis and Cluster–Adsorbate Coupling methods. Stretching and bending frequencies are both shifted by the side by side interactions. The coupling of surface phonons and adsorbate vibrations reduces the side effects. The largest side effects on the vibrational internal energy, isochoric heat capacity, entropy and total Helmholtz free energy of adsorbed CO molecule calculated using the CAC method are found for 0.5 ML coverage. The results of the CAC method are better, but the PHA method can be used as a simple upper bound estimation. The adsorptive phase acts as an intelligent material in such a way that it changes its configuration in order to reduce the side effects.     

Optical properties of new 5-(4-phenylethynyl)-substituted-1,10-phenanthroline derivatives

The synthesis and optical properties of a novel family of 5-substituted-1,10-phenanthroline derivatives are reported herein. One carbon-carbon triple-bond function was introduced using a Sonogashira cross-coupling reaction. The effects on optical properties, of the substitution with electro-withdrawing or -donating substituents in the 5th position of the 1,10-phenanthroline are investigated. Experimental chemical structure-polarisability relationship is analyzed according to the Lippert-Mataga correlation and compared to a theoretical study carried out with DFT calculations. These compounds are promising candidates for a fine-tuning of the internal charge-transfers but also as potential nonlinear chromophores and ligands within multifunctional coordination complexes.