Electrochemical Tuning of Electronic Structure of C_(60) and C_(70) Fulleren Peapods: In Situ Visible Near-Infrared and Raman Study

摘要

The population of valence-band electronic states of fullerene peapods (C_(60)@SWCNT and C_(70)@SWCNT) was tuned electrochemically in 0.2 M LiClO_4 + acetonitrile. Electrochemistry of peapods is dominated by their capacitive charging without distinct faradaic processes. In situ vis-NIR spectra of C_(60)/C_(70) peapods are similar to those of empty nanotubes. Electrochemical charging causes reversible bleaching of the transitions between Van Hove singularities. This bleaching is mirrored by quenching of resonance Raman spectra in the regions of tube-related modes. The Raman modes of intratubular C_(60) exhibit considerable intensity increase upon anodic doping of peapods, but these Raman modes are not enhanced at cathodic charging. In contrast to that, C_(70)@SWCNT does not show any enhancement of Raman intensities at both anodic and cathodic potentials. All the relevant Raman modes of intratubular C_(70) show symmetric charge-transfer bleaching as the tube-related modes. A suggested interpretation follows from model calculations of electronic structure of C_(70)@SWCNT (17,0) and C_(60)@SWCNT (17.0).