Synthesis of an Ultra-Bright Rotaxane with Threaded BODIPY Stoppers

A boron-assembled rotaxane featuring two novel stoppers consisting of threaded BODIPYs was synthesized. Its precursor, containing three boron atoms, is nonfluorescent. To break the covalent bonds between the macrocycle and the axle, the selective removal of one of the three boron atoms was achieved using potassium hydroxide. This deborylation triggers the system's fluorescence, resulting in a highly fluorescent rotaxane with a fluorescence quantum yield of 64%. Combined with a high absorption coefficient, this rotaxane exhibits a high brightness of 1.24 × 10⁵ mol^-1·L·cm^-1.