Abstract

The Light Emitting Polymer, Poly(2-Methoxy 5-(2-Ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) synthesised via Glich route process with addition of chain stopper to prevent gelation during polymerization was subjected to in-depth characterization. Since solvent interaction is critical in dynamic evolution process of conjugated polymer from solution to film, the present experimental investigation is focused on evaluating the solvent dependent optical properties of MEH-PPV. Photophysical studies indicate that MEH-PPV forms aggregate species with an absorption and luminescence spectra that are distinctly red-shifted from the intrachain exciton in aromatic solvents. The studies revealed better π-π interaction in aromatic solvents with the least conformational disorder facilitating improved charge transport, optical and electrical conductivity. While a ridge coiled structure in the case of dissolution in non-aromatic solvent increased the dielectric constant of MEH-PPV. The refractive index (~2.6) was not significantly affected by change in solvent polarity. The optical bandgap in aromatic solvent was lesser due to energy migration effect compared to non-aromatic solvent. The dipole-diploe interaction of MEH-PPV in non-aromatic solvent lead to formation of ridged coiled structure with torsional defection which lowered the quantum efficiency of MEH-PPV in non-aromatic solvent (17%) compared to aromatic solvent (24%). The SEM micrographs of thin films prepared from aromatic solvents illustrates smooth surface while surface of thin films from non-aromatic is rough. Additionally, films prepared from aromatic solvents were highly hydrophobic in nature with less porosity. Thus, the effect of non-aromatic solvent to improve the optoelectronic properties of MEH-PPV is though less important than aromatic solvents.

Keywords: MEH-PPV; Dielectric constant; Optical conductivity; Electrical conductivity