Light induced chemical and physical processes in small organic-/inorganic-/bio-molecules have been a subject of experimental and theoretical research for several decades. Recent advances in high resolution spatio-temporal techniques have offered detailed understanding of excited state processes in small molecules. In sharp contrast, however, information on electronic processes in biomolecules such as isolated proteins and DNA (and their complexes) is still in its infancy. Though extremely complicated to uncover, knowledge of photo-excited state processes of such biomolecules in the cellular/biological context is the eventual goal of scientists working in these areas.

Photochemical and photophysical processes in biomolecules are intimately involved in a multitude of functional processes, that include vision, photosynthesis, molecular recognition, gene replication, etc., and can be utilized in areas such as photodynamic therapy. Such processes in DNA are also of interest to both the biological and materials communities as memory devices and structural building blocks. Malign consequences of mis-function in higher life forms can include blindness (retinal pigmentosa), as well as photomutation leading, in DNA, to the primary cause of various types of cancer which (when light induced) can lead to melanomas.

At the higher level of biomolecular complexity, DNA-protein photolesions remain one of the least well characterised systems. Static and kinetic site-specific protein-DNA photocrosslinking has major implications for transcription in general, for the topology determinants specifically for RNA polymerase II transcription, and the mechanistic determinants of contacts involved in nucleoprotein complexes. Thus, description and detection of DNA–protein crosslinks (DPCs) by novel experimental, and explanation by theoretical, methods are timely topics for discussion.