The dipolar endofullerene HF@C60

The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage while minimizing escape of HF. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1H-19F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature-dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole

Engineering crystals of dendritic molecules

A detailed single-crystal X-ray study of conformationally flexible sulfonimide-based dendritic molecules with systematically varied molecular architectures was undertaken. Thirteen crystal structures reported in this work include 9 structures of the second-generation dendritic sulfonimides decorated with different aryl groups, 2 compounds bearing branches of both second and first generation, and 2 representatives of the first generation. Analysis of the packing patterns of 9 compounds bearing second-generation branches shows that despite their lack of strong directive functional groups there is a repeatedly reproduced intermolecular interaction mode consisting in an anchor-type packing of complementary second-generation branches of neighbouring molecules. The observed interaction tolerates a wide range of substituents in meta- and para-positions of the peripheral arylsulfonyl rings. Quantum chemical calculations of the molecule-molecule interaction energies agree at the qualitative level with the packing preferences found in the crystalline state. The calculations can therefore be used as a tool to rationalize and predict molecular structures with commensurate and non-commensurate branches for programming of different packing modes in crystal

Time-Dependent Density Functional Tight Binding: New Formulation and Benchmark of Excited States

A new formulation of time-dependent density functional tight binding (TD-DFTB) is reported in this paper. It is derived from the application of the linear response theory to the ground state DFTB Hamiltonian, without the introduction of additional parameters for the description of the excited states. The method is validated for several sets of organic compounds, against the best theoretical estimates from the literature, density functional theory, semiempirical methods, and experimental data. The comparison shows that TD-DFTB gives reliable results both for singlet and triplet excitation energies. In addition, the application of TD-DFTB to open-shell systems shows promising results

Quantum dynamical simulations as a tool for predicting photoinjection mechanisms in dye-sensitized TiO 2 solar cells

On the basis of a time-dependent self-consistent density functional tight-binding (TD-DFTB) approach, we present a novel method able to capture the differences between direct and indirect photoinjection mechanisms in a fully atomistic picture. A model anatase TiO 2 nanoparticle (NP) functionalized with different dyes has been chosen as the object of study. We show that a linear dependence of the rate of electron injection with respect to the square of the applied field intensity can be viewed as a signature of a direct electron injection mechanism. In addition, we show that the nature of the photoabsorption process can be understood in terms of orbital population dynamics occurring during photoabsorption. Dyes involved in both direct (type-I) and indirect (type-II) mechanisms were studied to test the predictive power of this method. © 2012 American Chemical Society.Fil: Oviedo, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Zarate, Ximena. Universidad Andrés Bello; ChileFil: Negre, Christian Francisco Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Schott, Eduardo. Universidad Andrés Bello; ChileFil: Arratia Pérez, Ramiro. Universidad Andrés Bello; ChileFil: Sanchez, Cristian Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin