title: Aggregation Control of α-Sexithiophene via Isothermal Encapsulation Inside Single-Walled Carbon Nanotubes.
abstract: Liquid-phase encapsulation of α-sexithiophene (6T) molecules inside individualized single-walled carbon nanotubes (SWCNTs) is investigated using Raman imaging and spectroscopy. By taking advantage of the strong Raman response of this system, we probe the encapsulation isotherms at 30 and 115 °C using a statistical ensemble of SWCNTs deposited on a oxidized silicon substrate. Two distinct and sequential stages of encapsulation are observed: Stage 1 is a one-dimensional (1D) aggregation of 6T aligned head-to-tail inside the nanotube, and stage 2 proceeds with the assembly of a second row, giving pairs of aligned 6Ts stacked together side-by-side. The experimental data are fitted using both Langmuir (type VI) and Ising models, in which the single-aggregate (stage 1) forms spontaneously, whereas the pair-aggregate (stage 2) is endothermic in toluene with formation enthalpy of ΔHpair= (260 ± 20) meV. Tunable Raman spectroscopy for each stage reveals a bathochromic shift of the molecular resonance of the pair-aggregate, which is consistent with strong intermolecular coupling and suggestive of J-type aggregation. This quantitative Raman approach is sensitive to roughly 10 molecules per nanotube and provides direct evidence of molecular entry from the nanotube ends. These insights into the encapsulation process guide the preparation of well-defined 1D molecular crystals having tailored optical properties.
authors: Etienne
authors: E
authors: Gaufrès
authors: Nathalie Y-W
authors: NY
authors: Tang
authors: Alexandre
authors: A
authors: Favron
authors: Département de Génie Physique, Polytechnique Montréal , Montréal, Quebec H3C 3A7, Canada.
authors: Charlotte
authors: C
authors: Allard
authors: François
authors: F
authors: Lapointe
authors: Laboratoire Charles Coulomb (L2C) UMR 5221, CNRS-Université de Montpellier , Montpellier 34090, France.
authors: Vincent
authors: V
authors: Jourdain
authors: Laboratoire Charles Coulomb (L2C) UMR 5221, CNRS-Université de Montpellier , Montpellier 34090, France.
authors: Saïd
authors: S
authors: Tahir
authors: Colin-Nadeau
authors: CN
authors: Brosseau
authors: Richard
authors: R
authors: Leonelli
authors: Richard
authors: R
authors: Martel
keywords: Raman spectroscopy and imaging; aggregation; carbon nanotubes; dyes; isotherms; liquid-phase encapsulation; α-sexithiophene