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

Three 4-(benzo[d]thiazol-2-y1)-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 Cr3+, Al3+, Zn2+ and F- ions with large Stokes shifts. Furthermore, under optimal conditions, the detection limit of probe L towards Cr3+, Al3+, Zn2+ 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 'H NMR titration experiments revealed that the recognition mechanism of probe L towards the ions Cr3+, Al3+, Zn2+ and F- were different. The presence of Cr3+ and Al3+ recovered the ESIPT, but the presence of Zn2+ 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 Cr3+, Al3+ and Zn2+ ions has been demonstrated.