Conjugated polymers are wide bandgap semiconductors which have a series of conjugated π-orbitals that extend along the polymer ‘backbone’. The π-orbital conjugation can be disrupted by twisting of the polymer, affecting their optical properties. These materials are very useful for devices, where they are frequently found in semicrystalline thin films. In thin films, Frenkel excitons diffuse on a nanometer scale. However, measurement of the diffusion length of excitons in conjugated polymer films is currently very difficult. Disordered packing and twisting of polymers plays a significant role, but has not been examined in detail. This dissertation presents methods of measuring exciton diffusion length in polymer films and nanoparticles and explains the effect of nuclear disorder on the optical spectra and exciton diffusion in semicrystalline polymer films.