The one-dimensional structure of single-walled carbon nanotubes (NT) display optical absorption and near-infrared emission (thanks to van Hove singularities). Chromophore encapsulation into host single-walled carbon nanotubes allows to create hybrid nano-systems with tunable opto-electronic properties. Up to now, we have been confining different kinds of chromophores,1-4 absorbing from the blue/ green (400/500 nm) range (tetracyanoquinodimethane (TNCQ), quaterthiophene derivatives (4T) and tetramethyl-paraphenylenediamine (TMPD)) to the red (700 nm) range (phthalocyanine (MPc)). In addition then can be either electron donor (4T, TMPD) or acceptor (TNCQ). In this study, we investigate, at both the macroscopic and the individual scales, the electronic and the optical properties of our hybrid systems by means of Raman and photoluminescence spectroscopies. Photoluminescence experiments clearly demonstrate changes on the emission properties after encapsulation. The intensities can be increased or reduced depending on the nature of the confined chromophores (electron donor or acceptor) and on the NT diameter. From Raman measurements, a significant charge transfer from the confined dye to the nanotube is evidenced. The main relevant parameters that govern the charge transfer are the nanotube diameter and the nature of the chromophores (electron donor or acceptor). Therefore, Raman and photoluminescence experiments strongly suggest charge transfer between the confined molecules and the nanotubes, leading to a Fermi level shift which governs the radiative de-excitation efficiency.

The polarized fluorescence emission of organic fluorophores has been extensively studied in photonics and is increasingly exploited in single molecule scale bio-imaging. Expanding the polarization properties of compact molecular assemblies is, however, extremely challenging due to depolarization and quenching effects associated with the self-aggregation of molecules into the sub-nanometer scale. Here we demonstrate that Boron Nitride Nanotubes (BNNTs) can act as a 1D host-template for the alignment of encapsulated a-sexithiophene (6T) inside BNNTs, leading to an optically active 6T@BNNT nanohybrid. We show that the fluorescence from the nanohybrid is strongly polarized with extinction ratios as high as 700 at room temperature. A statistical analysis of the 6T orientation inside BNNTs with inner diameter up to 1.5 nm shows that at least 80% of the encapsulated 6Ts exhibit a maximum deviation angle of less than 10{\deg} with respect to the BNNT axis. Despite a competition between molecule-molecule and molecule-BNNT adsorption in larger BNNTs, our results also show that more than 80% of the molecules display a preferential orientation along the BNNT axis with a deviation angle below 45{\deg}.

The field of ion transport through carbon nanotubes (CNTs) is marked by a large variability of the ionic conductance values reported by different groups. There is also a large uncertainty concerning the relative contributions of channel and access resistances in the experimentally measured currents, both depending on experimental parameters (nanotube length and diameter). In this perspective article, we discuss the ionic conductance values reported so far in the case of 2 individual CNTs and compare them with standard nano-fluidic models considering both the access and channel resistances. With a view toward guiding experimentalists, we thus show in which conditions the access or the channel resistance can predominate in CNTs. We explain in particular that it is not justified to use phenomenological models neglecting the channel resistance in the case of micrometer-long CNTs. This comparison reveals that most experimental conductance values can be explained in the framework of current nanofluidic models by considering experimental variations of slip length and surface charge density and that just a few extraordinarily high values cannot be accounted for even using extreme parameter values. Finally, we discuss how to complete existing models and how to improve the statistical reliability of experimental data in the field.

Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes, are custom made nanotubes with controlled diameter, morphology and organization. These nanotubes undergo major structural changes at high temperatures. Here, we report a complete analysis of the structural transformation of single and double-walled aluminogermanate nanotubes, organized or not in bundles, up to 800 • C. Complementary X-ray scattering and spectroscopy experiments were performed. The evolution of both Al and Ge atoms coordination during the transformation process was studied in-situ. Quantitative analysis of X-ray absorption spectra reveals that the dehydroxylation of nanotubes leads to intermediate stages of 'metaimogolite', which differ in the coordination of the aluminium atoms. A mechanism explaining the major structural reorganization is proposed based on atomic jump processes.