The present invention describes 7-aminocoumarin dyes that are substituted one or more times at the 3-, 6- and/or 8-positions by a sulfonic acid or a salt of a sulfonic acid, said dyes being useful as fluorescent probes or in the preparation of enzyme substrates, caged probes, or adducts with reducing sugars. The dyes of the invention optionally possess a reactive group useful for preparing fluorescent conjugates, which conjugates and methods for their preparation are described herein.