Simplified Synthetic Route to Doped Oligothiophenes in Carbon Nanotubes

Oligothiophene (OT) molecules encapsulated in semiconducting carbon nanotubes are promising candidates for coated molecular wires. Previous synthesis of OT within single-walled carbon nanotubes (SWNTs) has relied on vapor-phase methods, which requires evacuation of reaction system. This study demonstrates a simplified liquid-phase method involving the immersion and heating of SWNTs in 2,5-dibromothiophene. The formation of OT molecules and their positive monovalent cations was verified using scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, optical reflection spectroscopy, and Raman scattering spectroscopy. The filling fractions of the neutral OT molecules and cations in the SWNTs were estimated using the Drude–Lorentz model analysis of the optical reflection spectra. These estimated filling values are significantly higher than those reported in a previous study using the vapor-phase method.