Conjugated-Polyelectrolyte-Functionalized Reduced Graphene Oxide with Excellent Solubility and Stability in Polar Solvents

Conjugated-polyelectrolyte (CPE)-functionalized reduced graphene oxide (rGO) sheets are synthesized for the first time by taking advantage of a specially designed CPE, PFVSO3, with a planar backbone and charged sulfonate and oligo(ethylene glycol) side chains to assist the hydrazine-mediated reduction of graphene oxide (GO) in aqueous solution. The resulting CPE-functionalized rGO (PFVSO3-rGO) shows excellent solubility and stability in a variety of polar solvents, including water, ethanol, methanol, dimethyl sulfoxide, and dimethyl formamide. The morphology of PFVSO3-rGO is studied by atomic force microscopy, X-ray diffraction, and transmission electron microscopy, which reveal a sandwich-like nanostructure. Within this nanostructure, the backbones of PFVSO3 stack onto the basal plane of rGO sheets via strong pi-pi interactions, while the charged hydrophilic side chains of PFVSO3 prevent the rGO sheets from aggregating via electrostatic and steric repulsions, thus leading to the solubility and stability of PFVSO3-rGO in polar solvents. Optoelectronic studies show that the presence of PFVSO3 within rGO induces photoinduced charge transfer and p-doping of rGO. As a result, the electrical conductivity of PFVSO3-rGO is not only much better than that of GO, but also than that of the unmodified rGO.