Charge-transfer and excitonic energy transfer dynamics play important roles in the photophysics of a wide range of chemical and material systems. In this talk I shall discuss our recent work in developing theoretical tools for describing such processes in semiconducting organic systems. In particular, I shall discuss the generation of secondary excitons at the heterojunction interface between segregated semi-conducting polymer domains. I shall also descibe how we have extended our techniques to study the ultrafast energy transfer dynamics in model DNA strands, highlighting some recent results