Phonons in the crystalline phase of 2,2'-bithiophene (2T) are investigated using the direct method combined with density functional theory (DFT)based total energy calculations. Phonon calculations are performed as a function of the long range interactions and the displacement amplitude used for calculating Hellmann-Feynman forces. For the first time, we show that both these parameters are crucial in simulating accurately the experimental low-frequency density-of-states of the 2T crystalline phase, obtained from inelastic neutron scattering experiments. The DFT/direct method approach allows the anharmonicity of phonons to be investigated. The anharmonic behaviour of the low-frequency vibrational modes (below 300 cm(-1)) as the high-frequency - vibrational modes at 685, 800 and 885 cm(-1) of the 2T crystalline phase is clearly demonstrated. Except for these three latter high-frequency modes, a harmonic behaviour is observed for the intramolecular modes. The calculation of the multiphonon contribution predicts the appearance of a broad background in the 600-1500 cm(-1) frequency range, as well as defined features around 950 and 1130 cm(-1), in good agreement with the inelastic neutron scattering data. Finally, low-frequency dispersion curves are given.

X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) investigations have been performed to study the self-assembly properties of lamellar organic–inorganic bridged silsesquioxanes. The organic part consists of an alkylene chain (flexible spacer) between two urea groups. For this study, two samples with different chain length (six and twelve carbon atoms) were synthesized. It is pointed out that the self-assembly properties of the organic component are controlled both by the hydrophobic interactions between alkylene chains and by the hydrogen bonds between urea groups. Infrared results clearly show a direct correlation between the strength of the hydrogen-bond and the crystallinity of the organic–inorganic hybrid materials. Furthermore, the study of the asymmetric stretching CH2 correlated with XRD results indicate that the disorder along the alkylene chain decreases with longer chain length.

A new method has been developed for the synthesis of shaped-controlled bridged silsesquioxanes by the acid hydrolysis of urea-derived silylated precursors. This method is based on the ability of the hydrogen bonds of the urea groups to organize the molecules in a supramolecular architecture and provides after hydrolysis a new access to hybrid materials with controlled morphologies. A chirality transcription from a molecular precursor to a hybrid solid has been achieved. A right- and a left-handed helices have been obtained respectively from the chiral (R,R)- and the (S,S)-enantiomers of the diureido derivatives of trans-diaminocyclohexane. In a related way, a long range ordered hybrid solid has been obtained. Long carbon chain as spacer between the urea groups of the precursor affords lamellar hybrid silicas.

We study the Raman spectra of Li-doped SWNT films. A monotonic upshift of the tangential modes, and a concomitant progressive loss of the resonant behavior of the Raman signal, are evidenced when the Li rate increases. No significant change is observed all over the temperature range 10-300K. (C) 2002 Elsevier Science B.V. All rights reserved.