The bases that make up the DNA double helix absorb ultraviolet light. There is much debate about the way nature avoids radiation damage to DNA. Furthermore, the unique characteristic of an organized sequence of closely spaced base pairs, exploited in living organisms, can be used to tune the electronic structure for photo physical functionality in future applications. To understand the special properties of the DNA double helix that make it possible to avoid radiation damage, and their use in applications, new state of the art laser experiments are in progress in the host group. However, although these experiments give a wealth of information about the properties of DNA, due to their highly complex nature their interpretation is far from straightforward. New theory is necessary to interpret these measurements. This project aims at the establishment of a unique collaboration between theory and experiment to understand how the closely spaced DNA bases control its optical properties, and how manipulation of the base sequence can be exploited for applications. In particular, the transport of energy through the helix after absorption of light and the possibility of charge separation will be clarified. To this end, a new theory will be developed in close collaboration with experimental work. The theory will find direct application to DNA, but will also be applicable to related systems such as conjugated polymers and biological light-harvesting complexes, where both energy transport and charge separation are directly relevant for the function.