A multifunctional tripodal fluorescent probe for the recognition of Cr3+, Al3+, Zn2+ and F− with controllable ESIPT processes

Abstract Three 4-(benzo[ d ]thiazol-2-yl)-2,5-dihydroxybenzaldehyde fluorophores were introduced to construct a tripodal multifunctional ESPIT fluorescence probe L . The fluorescent analysis revealed that probe L exhibited excellent recognition capabilities towards Cr 3+ , Al 3+ , Zn 2+ and F − ions with large Stokes shifts. Furthermore, under optimal conditions, the detection limit of probe L towards Cr 3+ , Al 3+ , Zn 2+ and F − were low, of the order of 10 −8  M, which indicated that probe L was sensitive to these four ions. Interestingly, the fluorescent and 1 H NMR titration experiments revealed that the recognition mechanism of probe L towards the ions Cr 3+ , Al 3+ , Zn 2+ and F − were different. The presence of Cr 3+ and Al 3+ recovered the ESIPT, but the presence of Zn 2+ trigger a moderate deprotonation of the phenolic OH and induced an ESIPT red-shifted (60 nm) emission wavelength. Finally, the presence of F − completely deprotonated the free phenolic OH and a remarkable red-shifted (130 nm) ESIPT emission was observed. In other words, the ESIPT process of probe L is controllable. Furthermore, the utility of probe L as a biosensor in living cells (PC3 cells) towards Cr 3+ , Al 3+ and Zn 2+ ions has been demonstrated.