Classical heterocycles with surprising properties: the 4-hydroxy-1,3-thiazoles

4-Hydroxy-1,3-thiazoles 1, being ‘classical’ heterocycles, revealed unexpected physicochemical properties. The compounds show pH-sensible fluorescence, which can be employed for the generation of white emission light. NMR data and quantum chemical results provide a better insight into the keto-enol-tautomerism and the nature of the chromophoric system.