Raman spectral features of longer polyynes HC2 nH (\({\sf n=4}\)–8) in SWNTs

Size-selected linear hydrocarbon molecules, polyynes HC2nH, were contacted in solutions with single-wall carbon nanotubes (SWNTs) prepared from laser-ablated metal/carbon composite rods (Rh/Pt/C) to produce polyyne-encapsulating SWNTs, HC2nH@SWNT(RhPt). New Raman spectral features were observed at 2120, 2061, 2017, 1982, and 1963 cm-1 for five polyynes of n=4–8, respectively, and identified as the vibrational excitation of symmetric stretching modes of the molecules inside the SWNTs. The Raman spectra were compared with those observed for polyynes on Ag islands (SERS) and in solutions. The filling factor was investigated from the concentration dependence of the Raman intensity for HC10H@SWNT(NiCo) to give an estimate of one polyyne molecule per ~350 carbon atoms of SWNTs, providing a picture for head-to-tale filling of aligned C10H2 molecules inside the SWNTs.