3-Hydroxychromone dyes exhibiting excited-state intramolecular proton transfer in water with efficient two-band fluorescence

We demonstrate that newly synthesised 7-acetamido-3-hydroxychromones, as well as their parent 3-hydroxychromone (3HC) analogues, exhibit excited-state intramolecular proton transfer reaction in polar protic media including water, resulting in well-resolved two-band fluorescence. Among all 3HCs reported so far, the new compounds show the highest quantum yields ever reported in water (4-13%), while maintaining the sensitive ratiometric response to solvent polarity. This makes them very promising precursors for the development of two-band fluorescent labels and probes, operating in water and other protic media.