Infrared dichroism studies and anisotropic photoluminescence properties of poly(para-phenylene vinylene) functionalized reduced graphene oxide

Two methods were used for the synthesis of composites based on reduced graphene oxide (RGO) and poly(para-phenylene vinylene) (PPV) in un-doped and doped state, respectively, i.e. the annealing conversion (AC) of the PPV precursor solution (PS) at 300 degrees C and the electropolymerization (E) of alpha, alpha, alpha', alpha'-tetrabromo-p-xylene. In the case of the E method, a decrease in the distyrylbenzene (DSB) weight onto the RGO sheet surface in favor of PPV in doped state is demonstrated by the s and p polarized IR spectroscopy. The change of the orientation angle of the transition dipole moment vector for the IR bands at 835 and 964 cm(-1), in the case of the AC of the PPV PS, is a result of the p-p* interactions between the phenyl groups of PPV and the RGO sheets. The photoluminescence (PL) bands at 2.42 and 2.26 eV indicate the formation of PPV macromolecular chains (MCs) with lengths of 5 and 710 repeating units (RUs), respectively. The anisotropic PL studies performed on the composites RGO/PPV in un-doped and doped state, respectively, highlight an increase of the wrapping angle of RGO sheets with PPV MCs with lengths of 5 RUs, when graphene concentration increases.