Exciton-phonon coupling and disorder profoundly influence the photophysical properties of aggregates, thin films and crystals of thiophene and phenylene vinylene based oligomers and polymers. Calculations of the photoluminescence spectrum in model herringbone aggregates are presented, based on a Holstein-type Hamiltonian accounting for the coupling of one or more totally symmetric intramolecular vibrational modes (phonons) to the main optical transition. Structural and point defects are also included. The model predicts unique properties for the 0-0 emission in comparison to the side-band emission in excellent agreement with experiment.