Opto-electronic properties of single-walled carbon nanotubes can be significantly modified by chromophore confinement into their hollow core. This study deals with quaterthiophene derivatives encapsulated into nanotubes displaying different diameter distributions. We report a significant electron transfer from the confined molecules to the nanotubes in our hybrid systems, evidenced by photoluminescence and Raman investigations. This charge transfer leads to an important enhancement of the photoluminescence intensity by a factor of nearly five depending on the tube diameter. Energy shifts observed on both absorption and emission on the hybrid system also depend on the nanotube diameters and are interpreted in terms of local structure of the confined molecules. The Raman G-band of hybrid systems exhibits a drop in intensity and significant shifts whose magnitude and direction strongly depend on the nanotube diameter. These behaviors are consistent with a weak electron transfer from the molecule to the tube, in good agreement with the PL analysis. In addition, close to the molecule resonance, the magnitude of the G-band shifts are modified and the intensity loss is amplified, strongly suggesting a photo-induced electron transfer. Finally, the Breit-Wigner-Fano lineshape (characteristic of electron-phonon coupling) of the Raman G-band is strongly reduced for defective metallic nanotubes. After molecule functionalization, this peculiar profile is recovered, suggesting a back donation of electrons to the nanotube. Thus, confinement species into nanotubes allow moving the Fermi level and consequently to monitor their opto-electronic properties.

NMR spectroscopy has been established as a potent method for the detn. of foldamer structures in soln. However, the NMR techniques could be limited by averaging, so addnl. exptl. techniques are often needed to fully endorse the folding properties of a sequence. The authors have recently demonstrated that oligo-​γ-​peptides composed of 4-​amino(methyl)​-​1,​3-​thiazole-​5-​carboxylic acids (ATCs) adopt an original helical fold stabilized by hydrogen bonds forming C9 pseudocycles. The main objective of the present work is to restudy the folding of ATC oligomer 1 to identify reliable FTIR and NMR structural markers that are of value for tracking the degree of organization of ATC-​based peptides.

The highly constrained b-amino acid ABOC induces different types of helices in b urea and 1:1 a/b amide oligomers. The latter can adopt 11/9- and 18/16-helical folds depending on the chain length in solution. Short peptides alternating proteinogenic a-amino acids and ABOC in a 2:1 a/b repeat pattern adopted an unprecedented and stable 12/14/14-helix. The structure was established through extensive NMR, molecular dynamics, and IR studies. While the 1:1 a-AA/ABOC helices diverged from the canonical a-helix, the helix formed by the 9-mer 2:1 a/b-peptide allowed the projection of the a-aminoacid side chains in a spatial arrangement according to the a-helix. Such a finding constitutes an important step toward the conception of functional tools that use the ABOC residue as a potent helix inducer for biological applications.

Opto-electronic properties of single-walled carbon nanotubes can be significantly modified by chromophore confinement into their hollow core. For instance, charge transfers are evidenced from Raman data analysis. First, by exciting nanotubes far from the optical absorption of the molecule, the Raman G-band signal exhibits a weak but significant up or downshift depending on the nanotube diameters. This behavior is consistent with a permanent electron transfer to the nanotube in the framework of the renormalization process 1. In addition, close to the molecule resonance, the magnitude of the G-band shift is enhanced for small diameter tubes, evidencing a photo-induced electron transfer. Finally, the Breit-Wigner-Fano lineshape (characteristic of electron-phonon coupling) of the Raman G-band can be strongly reduced for defective metallic nanotubes. After molecule functionalization, this peculiar profile is recovered, suggesting a back donation of electrons to the nanotube. Photoluminescence properties of semiconducting nanotubes are also significantly modified by chromophore confinement. The nanotube emission intensity is amplified after encapsulation. This exaltation depends on the nanotube diameter, and can be related to diameters exactly fitting the molecule size. The origin of the photoluminescence enhancement will be discussed.

Binary c–T phase diagrams of organogelators in solvent are frequently simplified to two domains, gel and sol, even when the melting temperatures display two distinct regimes, an increase with T and a plateau. Herein, the c–T phase diagram of an organogelator in solvent is elucidated by rheology, DSC, optical microscopy, and transmitted light intensity measurements. We evidence a miscibility gap between the organogelator and the solvent above a threshold concentration, cL. In this domain the melting or the formation of the gel becomes a monotectic transformation, which explains why the corresponding temperatures are nonvariant above cL. As shown by further studies by variable temperature FTIR and NMR, different types of H-bonds drive both the liquid–liquid phase separation and the gelation.

Wet acid oxidation treatment methods have been widely reported as an effective method to purify and oxidize the surface of industrial multi-walled carbon nanotubes (MWCNT). This work examines the use of a concentrated HNO3/H2SO4 mixture in an attempt to optimize the purification procedure of industrial MWCNT with diameter distribution statistics. It is shown that acid treatments of several hours are enough to purify the nanotubes. The electrical and thermal conductivities of epoxy composites containing 0.05-0.25 wt. % of acid-treated MWCNT has been studied. The electrical conductivity of the composites decreases by more than three orders, whereas the thermal conductivity of the same specimen increases very modestly as a function of the filler content.

Semiconducting carbon nanotubes are an emerging material for photonics. We report on the enhancement of semiconducting carbon nanotubes photoluminescence with silicon microring resonators. Polyfluorene extracted semiconducting carbon nanotubes, deposited on such resonators, display sharp emission peaks superposed to nanotube emission, which is attributed to the interaction with the cavity modes of the microring resonators. Ring resonators with radii of 5 and 10  μm were used, to demonstrate the tuning of the spectral distance between two successive emission resonances. Quality factors ranged between 3000 and 4000 in emission. These are among the highest values reported so far for carbon nanotubes coupled with optical microcavity on the silicon platform, highlighting the bright perspectives for carbon nanotube photonics.