Synthesis of an ultra-bright rotaxane with threaded BODIPY stoppers

Two new boron-assembled rotaxanes were successfully synthesized. One of them possesses two stoppers of a new kind consisting of threaded BODIPYs. Its precursor bearing three boron atoms is non fluorescent. To release the macrocycle, the selective removal of one boron out of the three was achieved in high yield using potassium hydroxide. The removal of this boron triggers the fluorescence of the system, making this rotaxane highly fluorescent, with a fluorescence quantum yield of 64%. Combined with a high absorption coefficient, this rotaxane is one of the brightest reported so far with a brightness of 1.24 x 10^5 mol-1.L.cm-1.