Rigidized 3-aminocoumarins as fluorescent probes for strongly acidic environments and rapid yeast vacuolar lumen staining: mechanism and application

Abstract

Coumarins remain one of the most important groups of fluorescent bio-probes, thanks to their high quantum yields, moderate photostability, efficient cell permeation and low (cyto)toxicity. Herein, we introduce new 3-aminocoumarins as turn-on pH probes under strongly acidic conditions and for indicators capable of significantly improving yeast vacuolar lumen staining compared to the commercial CMAC derivatives. We present the details of the on–off switching mechanism revealed by the TD-DFT and ab initio calculations complemented by a Franck–Condon analysis of the probes’ emission profiles.