Optical properties of fullerene and non-fullerene peapods

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 C(60) and 72% filling for C(70) 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 C(60) inside nanotubes by blue-laser irradiation, suggesting molecular rotation inside them. In C(70) peapods, no photopolymerization was observed but the relative Raman intensity of each peak is different from the C(70) 3D crystal. This is probably caused by mixing of two different crystal structures in C(70) peas. Furthermore, we synthesized Zn-diphenviporphyrin peapods. Optical absorption and Raman spectra suggest that the encapsulated molecules are deformed by interaction with the SWNT.