Although diverse photostability mechanisms exist, organic dyes – often used as drugs or pollutants – can induce damages to biological media through indirect light absorption. Hence, understanding the underlying mechanisms involved in photosensitized damage is crucial to describe and possibly anticipate photobiological risks, as well as to design anticancer phototherapies [1].

Here, I present the results concerning our latest studies on different reactivities induced by common organic dyes, through multiscale molecular modelling techniques. Especially, the effects on models of B- DNA, Rhodopsin (the protein involved in the primary event of mammalian vision) and biological membranes will be shown. Depending on the target and on the preferred reactivity, different dyes are considered: the photochemistry of benzophenone – a paradigmatic DNA photosensitizer [2] – and its implications in the competitive processes of hydrogen abstraction [2] and energy transfer to DNA [3] will be described.

Electron transfer is also considered by the interaction of DNA with two fluorescent dyes widely used in cellular biology: nile blue and nile red [4,5]. Finally, the potentialities of a recently synthesized novel carbazole in photosensitizing DNA through two-photon absorption will be reported. Especially, it will be shown how it can undergo photoionization with the production of a solvated electron [6].

On the other hand, extended π-conjugated systems as hypericin [7] and chlorin-e6 [8], are studied when in contact with a model lipid bilayer, elucidating their interaction modes and photosensitization mechanisms. Moreover, being chlorin-e6 a photoactive drug reported to enhance visual sensitivity as side effect, its binding modes to trans-membrane Rhodopsin are investigated, including the possible Förster resonance energy transfer (FRET) pathways to the retinal.