Synthesis of novel water‐soluble fluorescent coumarins bearing sulphonic and hydroxyl groups

Two dihydroxynaphtaldehydes (2,5-dihydroxynaphtaldehyde and 2,7-dihydroxynaphtaldehyde) and 2,4-dyhydroxybenzaldehyde were sulphonated. These intermediates were used in subsequent reactions with 2-cyanomethylbenzothiazole, 2-cyanomethylbenzoimidazole and 1-methyl-2-cyanomethylbenzoimidazole to synthesise sulphonated coumarin derivatives. The absorption and steady-state fluorescence characteristics of the prepared coumarins were studied in ethanol and in water.