Final Report Summary - PHOTORECEPTION (Photoactive proteins: from the intrinsic properties of biochromophores towards the ultra-fast excited-state reaction dynamics in photoreceptors) The project is aimed at studying photoactive proteins and their light-absorbing molecular units at the atomic level. Photoactive proteins are widespread in nature. Opsin proteins containing a protonated Schiff-base retinal (PSBR) chromophore are perhaps the best known as they provide vision in vertebrates. Unlike in the fields of chemistry and biochemistry we work with isolated species in vacuum. By using vacuum as the environment we anticipate new insight in the intrinsic properties of biological chromophores and the atomic-scale chromophore-protein interactions that play a key role for the functioning of photoactive proteins. The knowledge of the properties of the isolated building blocks is essential for our understanding how they function in a collaborative manner.The project has its focus areas on photo-initiated quantum molecular dynamics of biological chromophores from visual photoreceptors and members of the Green Fluorescent Protein (GFP) family. Besides their biological relevance, these systems provide a stage for in-depth studies of the fundamental processes, such as photo-induced isomerization coupled to internal conversion, photodetachment, photo-activated electron and proton transfer.Our strategy is to combine the expertise of the Marie-Curie fellow in the field of state-of-the-art electronic structure theory and multi-scale approaches with the leadership of the Aarhus University when it comes to ion-storage and laser-action spectroscopy techniques. The joint theoretical and experimental interdisciplinary studies are crucially important when tackling such complex systems. The new knowledge has been gained through the project, including a disclosure of the mode-specific electron-nuclear coupling mechanisms in the ultrafast dual photoresponse of the GFP chromophore anion; the detailed insights into the intrinsic photophysical properties of the PSBR chromophore, which shed light on the mechanism for color tuning in visual photoreceptors, thus explaining color vision; and unraveling the reaction mechanism underlying the selective photoresponse of the gas-phase PSBR chromophore, which adds up to our understanding of the role played by the protein in the primary step of vision. The project makes valuable contributions to the field of biological photoreception and paves the way for mode-selective photophysics and photochemistry in biosystems.The project publication summary includes 5 high-impact peer-reviewed publications, 4 manuscripts under submission and 1 book chapter in the series Physical Chemistry in Action (Springer, 2013). The dissemination activities also include 4 invited and 3 hot topic talks at the international conferences. The results of the project have been featured on the front cover of the Faraday Discussions 163 (2013). The direct benefits have been reaped through the project enabling access to the HPC resources at the European Community level through the fellow’s successful PRACE/DECI8 application.The project demonstrates a tight binding between theory and experiment that forms a firm ground for the long-term cooperation of the fellow with the host research group. The fellow has set up the international collaborations, also through the new European COST Action application. The fellow’s employment is extended for two more years, giving her a solid perspective for obtaining a permanent position, which will soon be open at the Department of Physics and Astronomy, Aarhus University, Denmark. The project website – http://phys.au.dk/forskning/forskningsomraader/amo/molecular-physics/research/marie-curie-project/.