Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly(p-phenylene vinylene) (PPV)-based derivatives. Due to chemical modifications the PPV derivatives differ by three orders of magnitude in charge carrier mobility as a result of a reduced energetic disorder. From the photoluminescence decay curves of PPV/fullerene heterostructures, the exciton diffusion coefficient was found to increase by one order of magnitude with decreasing disorder. This increase in the diffusion coefficient is compensated by a decrease of the exciton lifetime, leading to an exciton diffusion length of 5-6 nm for the various PPV derivatives.