Aggregation Control of α-Sexithiophene via Isothermal Encapsulation Inside Single-Walled Carbon Nanotubes.

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-...