Recently, reversibly photoswitchable fluorescent proteins (RSFPs) have been widely applied in super-resolved fluorescence microscopy, such as reversible saturable optical fluorescence transition (RESOLFT), a super-resolved microscopy technique that allows for a significant reduction in the illumination intensities and in photobleaching. Even though photo-physical parameters (switching, fluorescence quantum yields…) are linked to the resolution and image acquisition speed, the switching mechanism that controls these parameters is still a matter of debate. The most studied RSFP is Dronpa, a negative RSFP from Anthozoa (e.g. corals). Using a combination of time-resolved crystallography and transient absorption spectroscopy we studied the mechanism of off-to-on and on-to-off photoswitching in WT and different mutants of rsEGFP2 (e.g. jellyfish), a common protein used in super-resolved microscopy. We clarified the order of off-to-on photoswitching events, i.e. chromophore isomerization in the picosecond time scale with the formation of a twisted chromophore[1], and different ground-state steps with protein conformational changes and a deprotonation on the microsecond timescale[2, 3]. We will then discuss here our recent results for on-to-off switching and how the protein cage controls meaningful parameters for WT rsEGFP2 and mutants in comparison to other RSFPs: fluroescence and switching quantum yield [4].