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.