Optical properties of fullerene and non-fullerene peapods

Abstract.

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene peapods, were synthesized in high yield by using diameter-selected nanotubes as pods. Transmission electron microscopy revealed high-density fullerene chains inside the nanotubes. X-ray-diffraction measurements indicate 85% filling for C₆₀ and 72% filling for C₇₀ molecules as a total yield. Interestingly, C₆₀ peas do not show any thermal expansion while C₇₀ peas show normal behavior. Room-temperature Raman spectra show one-dimensional photopolymerization of C₆₀ inside nanotubes by blue-laser irradiation, suggesting molecular rotation inside them. In C₇₀ peapods, no photopolymerization was observed but the relative Raman intensity of each peak is different from the C₇₀ 3D crystal. This is probably caused by mixing of two different crystal structures in C₇₀ peas. Furthermore, we synthesized Zn-diphenylporphyrin peapods. Optical absorption and Raman spectra suggest that the encapsulated molecules are deformed by interaction with the SWNT.