Kinetic studies on visible-light-switchable photochromic fluorophores based on diarylethenes.

We present three recently developed photochromic fluorophores that are based on diarylethenes with elongated conjugated π-systems. The diarylethenes 1 and 3 can be switched from their open to their closed form with visible light. The diarylethenes 1 and 2 are covalently coupled to a standard rhodamine B-based fluorophore and act as photoswitchable resonance energy acceptors. By controlling their switching state, the fluorescence intensity of the dye can be modulated. The third compound 3 is a diarylethene that shows photoswitchable inherent fluorescence due to its stilbazolium-like structure. Ensemble experiments demonstrate that diarylethene-based photoswitches show superior characteristics regarding their switching performance, thermal stability and fatigue resistance. These attributes make them promising candidates for super-resolution imaging methods that are based on the determinate fluorescence switching of fluorophores between an off- and an on-state.