The recruited student will investigate the photophysical mechanisms of reversibly photoswitchable fluorescent proteins (RSFPs) employing solution NMR spectroscopy coupled with in-situ illumination and variable oxygen pressure. RSFPs are capable to switch between a fluorescent on-state and a nonfluorescent off-state under specific light illumination, and have fostered many types of imaging applications including super-resolution methods. Multidimensional NMR spectroscopy is a particularly powerful atomic resolution technique providing detailed information on conformational protein dynamics, as well as the local chemistry (protonation states, H-bonding interactions, …) involved in the photophysics of the chomophore within the protein scaffold. In the proposed PhD project, we intend to further improve our NMR in-situ illumination device by adding capabilities such as additional wavelengths of emitting light sources, fluorescence detection, and oxygen pressure control. This will allow to directly correlate the conformational dynamics of various states with their photophysical properties, as well as the effect of oxygen on triplet state formation and photobleaching. We will apply this NMR methodology to several green and red model RSFPs, as well as FAST systems. The goal will be to contribute fundamental knowledge of these fluorescent markers and to design improved variants.