Charge Transfer Evidence between Carbon Nanotubes and Encapsulated Conjugated Oligomers

A hybrid system consisting of quaterthiophene derivative inserted
into carbon nanotubes is studied. Encapsulation efficiency of the conjugated
oligomers in the hollow core of nanotubes is investigated by transmission
electron microscopy and spatial-resolved electron energy loss spectroscopy.
Infrared spectroscopy showed evidence of a significant positive charge transfer
on the inserted oligothiophene. Raman spectra display different behaviors
depending on the excitation energy and correlated to the quaterthiophene
optical absorption energy. At high excitation wavelength (far from the oligomer
resonance), radial breathing modes exhibit a significant upshift consistent with
an encapsulation effect. At low excitation wavelength (close to the oligomer
resonance), both the G-band shift and the low-frequency modes vanishing
suggest a significant charge transfer between the quaterthiophene and the
nanotubes.