Photo-active pi-conjugated molecules (quaterthiophene and phthalocyanine) are either encapsulated into the hollow core of single-walled carbon nanotubes or non-covalently stacked at their outer surface in order to elaborate hybrid nano-systems with new physical properties, providing practical routes to fit different requirements for potential applications. In this study, we are interested in the relationship between the structure and the opto-electronic properties. The structural properties are investigated mainly by x-ray diffraction and/or Transmission Electron Microscopy and Raman spectroscopy. We evidence that the supramolecular organizations of confined quaterthiophenes depend on the nanocontainer size whereas phthalocyanine encapsulation leads the formation of a 1D-phase for which the angle between the molecule ring and the nanotube axis is close to 32°. Confined phthalocyanine molecules display Raman spectra hardly altered with respect to the bulk phase, suggesting a rather weak interaction with the tubes. In contrast, the vibrational properties of the molecules stacked at the outer surface of tubes display important modifications. We assume a significant curvature of the phthalocyanine induced by the interaction with the tube walls and a change of the central atom position within the molecular ring, in good agreement with our DFT calculations.

In this theoretical work, we study the polarized infrared spectra of double-walled carbon nanotubes (DCNTs) as a function of their diameters, chiralities and lengths. For infinite DCNTs, mathematical relations are derived to estimate the diameter of the inner and outer tubes from the knowledge of their experimental mid-infrared spectra. The infrared spectra of DCNTs with a finite length are also calculated using the spectral moments method. We observe additional infrared bands as a function of the relative lengths of the inner and outer tubes. Bands located below 900 cm-1 give reliable information about these lengths.

The sol−gel preparation of a bridged silsesquioxane containingeuropium(III) salts and 2-thenoyltrifluoroacetone has been achieved from a newethane tetracarboxamide-based organosilane. Free-standing films with thicknessesup to 440 μm and maximum absolute quantum yield (q) of 0.34 ± 0.03(excitation at 320 nm) were prepared by the drop cast method, while thin films(∼200−400 nm) spin-coated on glass substrates led to highly luminescentcoatings with q = 0.60 ± 0.02 (excitation at 345 nm). The thin films were testedas planar luminescent solar concentrators and the optimized device displays anoptical conversion efficiency of 12.3% in the absorbing spectral region of theactive layer (300−380 nm).

Interaction rayonnement-matière

Formalisme de l'EXAFS

Nanotubes can be obtained from top down (Carbon nanotubes) or bottom up approaches (Organogels, self-structured bridged silsesquioxanes…). In most cases the nature of the nanotubes determines the vibrational spectroscopy technique best suited for the study of the physical properties of the nanomaterial. In this presentation, some examples are discussed. The coupling of Raman and/or infrared spectroscopies with ab initio calculations gives insights into both structural properties and self-assembling mechanisms of the nanomaterials. In the case of the encapsulation of foreign species in the hollow core of carbon nanotubes, resonant Raman spectroscopy allows studying the relation between size of the nano container and physical properties of the molecules under confinement (figure). Vibrational experiments were carried out under extreme conditions (diamond anvil cell technique for high pressure vibrational investigations). The pressure dependence of the Raman spectra allows assessing charge transfer properties between nanotube and encapsulated species under confinement. Infrared spectroscopy is a very powerful technique for the study of organogels of nanotubes and self-structured bridged silsesquioxane nanomaterials. The local and long range order structuring resulting from sol-gel reaction of organic or hybrid precursors have been investigated in situ using macro and micro IR spectroscopies in the middle and far infrared. The IR experiments are compared with density functional theory simulations.The significant contribution of synchrotron radiation for infrared studies of hybrid nanomaterials under extreme conditions is reported.

Confinement de complexes à transfert de charges à base d'iode dans les nanotubes de carbone