Polymer-Wrapped Carbon Nanotubes


Amphiphilic, linear conjugated poly[p-{2,5-bis(3-propoxysulfonicacidsodiumsalt)} phenylene]ethynylene (PPES) and poly[2,6-{1,5-bis(3-propoxysulfonicacidsodiumsalt)} napthylene]ethynylene (PNES) efficiently disperse single-walled carbon nanotubes (SWNTs) under ultra-sonication conditions into the aqueous phase.  Vis-NIR absorption spectroscopy, atomic force microscopy (AFM), and tunneling electron microscopy (TEM) demonstrate that these solubilized SWNTs are individualized.  AFM and TEM data reveal that the interaction of PPES and PNES with SWNTs gives rise to a self-assembled superstructure in which a polymer monolayer helically wraps the nanotube surface; the observed PPES and PNES pitch lengths confirm structural predictions made via MD simulations.

Following appropriate metatheses reactions, these self-assembled polymer-nanotube systems can be dissolved in organic solvents; electronic spectroscopy, transient absorption studies, as well as AFM and TEM data confirm that the PNES/PPES helical wrapping structure observed for individualized SWNTs in aqueous solution persists in nonaqueous media.  Related chiral semi-conducting polymers have been designed that provide individualized, single-chain-wrapped SWNTs that feature exclusively right- or left-handed helical superstructures.

These novel nanotube structures define new electroptically functional compositions as well as new tools to fabricate SWNT-based chiral materials.  These superstructures have been subjected to metathesis reactions with triethylammonium based ionic liquid modified chromophores.  Diphenylporphinato zinc derivative (ILPZn1), being one example, provides a simple proof-of-principle structure that shows that auxiliary redox centers can be noncovalently delivered to the SWNT backbone.  Pump-probe transient absorption spectroscopy reveals that the photo-excited porphyrin moiety decays via ET to SWNTs producing a long lived pophyrin cation radical species.  This Proof-of-principle study shows that other redox moieties can be predictably associated with semi-conducting polymer-wrapped SWNTs.