Development of a ratiometric fluorescent pH probe for cell imaging based on a coumarin–quinoline platform

• A new coumarin–quinoline-based ratiometric fluorescent pH probe is described.
• One major feature of the probe is that two emission peaks separate by >100 nm.
• The probe is useful for monitoring pH variations in living cells.

It is highly desirable to develop ratiometric pH probes with a well-resolved emission spectrum for biological imaging applications. In this work the design, synthesis, photophysical properties and cellular imaging studies of a new linked coumarin–quinoline probe is described. The major features of the novel probe include two well-resolved (>100 nm) emission peaks, strong fluorescence under acidic conditions, a pKa of 4.69, low cytotoxicity and good cell membrane permeability; features which render the probe useful for monitoring pH variations from neutral to acidic conditions in living cells.

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