Norbornadiene-bridged diarylethenes and their conversion into turn-off fluorescent photoswitches

We describe the synthesis and characterization of novel diarylethene photoswitches that contain a norbornadiene bridge and operate as p-type positive photochromes. One of the double bonds of norbornadiene is furthermore utilized to attach a fluoresceine tetrazine by an iEDDA cascade reaction, thereby forming a turn-off mode fluorescent photoswitch. A new class of reversible fluorogenic diarylethenes, assembled by iEDDA chemistry, with high switching efficiencies and quantum yields is described.