Electrochemical and chemical redox doping of fullerene (C-60) peapods

Different types of redox doping of C-60@SWCNT were monitored by Raman spectroscopy. Chemical doping was carried out by gaseous potassium, liquid potassium amalgam and gaseous fluorine diluted with argon. Electrochemical doping was investigated by in situ Raman spectroelectrochemistry in LiClO4 + acetonitrile solution and in 1-butyl-3-methylimidazolium tetrafluoroborate (ionic liquid). The peapods exhibit characteristic and complex feedback to chemical as well as to electrochemical doping. In contrast to chemical p-doping by F-2, the Raman scattering of intratubular fullerene is selectively enhanced during electrochemical p-doping. Similar selective enhancement is traced at chemical n-doping with gaseous potassium. Doping by gaseous potassium causes deep reduction of intratubular C-60 to C-60(6-), which is not fully re-oxidizable upon contact to air. On the other hand, doping with liquid potassium amalgam causes reduction of intratubular C-60 to C-60(4-) or C-60(5-), and complete re-oxidation to neutral fullerene occurs spontaneously upon contact to air. In general, the doping chemistry of peapods is significantly dependent on the applied redox potential, charge-compensating counterions and on the actual doping technique used. A critical review of the current data is provided. (C) 2005 Elsevier Ltd. All rights reserved.