Off–on–off fluorescent chemosensor for pH measurement with a terbium(iii) complex based on a tripodal salicylic-acid derivative

Abstract

New Tb(III) and Eu(III) complexes have been synthesized as potential pH probes using a tripodal substituted-salicylic ligand (H₃BSA). Among them, this carboxylate ligand is found to be a good sensitizer for Tb(III) emission owing to the superior match of the triplet energy level of the ligand with the ⁵D₄ emitting level of Tb(III). The resulting BSA·Tb complex exhibited high sensitivity in the physiological pH range with significant “off–on–off” fluorescence changes in aqueous solution. Furthermore, this unique rare-earth complex has been successfully used to monitor pH variations within HeLa cells and with filter papers.