Role of attached polymer chains on the vibrational relaxation of aC60fullerene in aqueous solution

Abstract

We have investigated the vibrational relaxation of a bare ${\mathrm{C}}_{60}$ fullerene and ${\mathrm{C}}_{60}$ fullerenes with covalently attached poly (ethylene oxide) (PEO) chains in aqueous solution using classical molecular dynamics simulations. The rate of transfer of vibrational energy from the excited fullerene to the surrounding water was found to be slow for the bare fullerene, with a vibrational relaxation time of approaching $200\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. Attachment of a single short PEO chain $({M}_{W}=250)$, yielding ${\mathrm{C}}_{60}$-PEO, was found to decrease the vibrational relaxation time by about a factor 5, while the vibrational relaxation time for a fullerene with six attached PEO chains, or ${\mathrm{C}}_{60}\text{\ensuremath{-}}{(\mathrm{PEO})}_{6}$, exhibited approximately 25 times faster vibrational relaxation than the bare fullerene. The temperature of the attached PEO chain(s) was found to increase during the vibrational relaxation of the fullerene, but remained well below that of the fullerene, indicating that the rate limiting step in vibrational relaxation of ${\mathrm{C}}_{60}$-PEO is energy transfer from the fullerene to the attached PEO.