Syntheses of three terbium complexes as fluorescent probes and their application on the pH detection of routine urine test

By modifying the salicylic-acid moiety with electron-withdrawing or –donating groups, three new terbium complexes (LI·Tb, LII·Tb, LIII·Tb) based on tripodal carboxylate ligands were synthesized. Due to different pull-push electronic effects of ligands, the fluorescence intensities of these terbium complexes significantly varied, that is: LII·Tb > LIII·Tb > LI·Tb. Meanwhile, the characteristic peaks at 492 nm (5D4 → 7F6) and 547 nm (5D4 → 7F5) showed “Off–On–Off” fluorescence response to various pH conditions, which indicated that all of them can be used as the highly sensitive pH fluorescent probes. Notably, using LII·Tb with the best fluorescence performance as a probe, some patients’ urine samples can be easily monitored through the response triggered by pH value. Therefore, LII·Tb has the potential to auxiliarily diagnose some diseases in clinical practice through pH detection of routine urine test.