Single-chain, helical wrapping of individualized, single-walled carbon nanotubes by ionic poly(aryleneethynylene)s: New compositions for photoinduced charge transfer reactions and photovoltaic applications
Amphiphilic, linear, semi-conducting aryleneethynylene polymers such as 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 transmission 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 superstructures 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. These well-defined nanotube-semi-conducting polymer hybrid structures can be further engineered to serve as electron transport elements in excitonic solar cells and function as electron acceptors in electron transfer reactions involving photoactivatable redox centers anchored to the SWNT backbone.
