New regioisomeric naphthol–thiazole based ‘turn-on’ fluorescent chemosensor for Al3+

Two new reactive and highly selective turn-on fluorescent chemosensors based on the position of ring annulation of the naphthalene–thiazole moiety for aluminum ions in ethanol, were synthesized and investigated. It was found that sensors 2 and 4 exhibited a remarkable enhancement of emission upon complexation with Al3+. A TD-B3LYP/6-31G(d,p) calculation was performed to characterize the nature of the fluorescence behavior of sensors 2 and 4 upon Al3+ complexation. The mechanism of fluorescence was based on the cation promoted hydrolysis of ester and subsequent complexation. The combination of experimental and computational analyses provides a more complete understanding of the molecular level origin of these types of unique photophysical properties.