Luminescence Excitation Spectroscopy in Poly(p-Phenylene-Vinylene) Derivatives: Implications for a Semiconductor Band VS. Exciton Model in Conjugated Polymers

Abstract High-resolution luminescence excitation spectroscopy (site-selective flourescence) results are presented for two soluble derivatives of poly(p phenylene-vinylene): poly(2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV), and poly(2,5-bis(cholestanoxy)-p-phenylene vinylene) (BCHA-PPV). Measurements have been performed on both thin films of these polymers, and dilute blends in polyethylene oriented by tensile drawing. By examining the effects of oxygen exposure in cast films, and the energy- dependence of the luminescence anisotropy in the oriented blends, we provide evidence that the electronic states in the absorption tail arise from localized states in an amorphous semiconductor.