Abstract: Organic semiconductor materials offer the potential of low-cost and flexible displays and lighting solutions, some of which have already made it to the marketplace. Despite this, much of the underlying optical physics remains poorly understood and hinders progress towards better and more powerful devices. In this talk, the basic properties of organic semiconductors will be reviewed and some of the outstanding issues explored. We will show how simple models based on dipole-dipole coupling can be validated (by comparison with quantum chemistry) and used to compute optical properties such as absorption, gain and luminescence spectra. Recent theoretical and experimental results on the optical pulse propagation and timescales of excitation transfer and hopping in linear oligoflourine and star-shaped samples will be also presented. Presented Thursday, September 20, 2012.