Pushing the limits of flash photolysis to unravel the secrets of biological electron and proton transfer.

Time-resolved absorption spectroscopy is a powerful tool to unravel biological functions and has been a key technology for elucidating the working of electron transfer chains in photosynthesis or photorepair of UV-damaged DNA. Both of these areas have seen important contributions from laboratories all over the world, not the least of them stemming from the ingenious technical advances described by Klaus Brettel, first at the Technical University of Berlin (Germany), and later at the Atomic Energy Agency in Saclay (France). Now, after more than forty years of tireless scientific activity, Klaus is approaching retirement and this collection gathers together tributes in the form of scientific contributions from colleagues along the way, covering a spectrum of topics as diverse as photosynthesis, light-induced DNA repair, electron and proton transfer in light signalling, flavin based photo-enzymology, fluorescent marker photophysics, synthetic models and modelisation, delicate sample transient absorption spectroscopy. In an era where science is increasingly changing context from "fundamental" to "applied", Klaus' curiosity and tenacity worked hand in hand in a most effective manner to further both technical possibilities and basic understanding.