Modulation of ICT and PET processes in boranil derivatives: a ratiometric fluorescent probe for imaging of cysteine

A novel ratiometric fluorescent probe 1 based on boranil derivatives modulated by ICT and PET processes was designed and synthesized for the first time. Upon addition of Cys, the emission peak of 1 changed from 461 nm to 474 nm, accompanied by a fluorescence color change from dark blue to blue under illumination with a 365 nm UV lamp. 1 exhibited a fast response (within 9 min), high sensitivity (detection limit of 95.1 nM) and excellent selectivity toward Cys over Hcy and GSH owing to a specific conjugate addition–cyclization reaction between Cys and the acrylate moiety. Furthermore, 1 was successfully implemented for monitoring Cys in living cells.