Imidazolyl-benzocoumarins as ratiometric fluorescence probes for biologically extreme acidity

A rational approach to develop a fluorescent probe for sensing biologically extreme acidity (pH <3) is disclosed. The probe, a push-full type 3-(imidazolyl)benzocoumarin dye, has the lowest pK(a) = 1.3 among ratiometric probes known so far, which is ascribed due to a unique sensing mechanism. The probe has high quantum yields, high chemical stability and good aqueous solubility. The probe was successfully applied to ratiometric fluorescence imaging of intrabacterial acidity from pH 4.0-1.0, offering a practical means for studying biological systems under the extreme pH conditions. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The rational approach to develop a fluorescent probe for sensing biologically extreme acidity is described. The probe, a push-full type 3-(imidazolyl)benzocoumarin dye, has the lowest pK(a) value among known ratiometric probes. The probe has high quantum yields, chemical stability and aqueous solubility, and it has been successfully used for ratiometric fluorescence imaging of intrabacterial acidity, providing a practical means for studying biological systems under extreme pH conditions.