Selective and pH‐Independent Detection of Ba²⁺ in Water by a Benzo‐21‐crown‐7‐Functionalized BODIPY

Abstract

Herein, we report on a highly Ba2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo‐21‐crown‐7 as a Ba2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba2+ induced fluorescence enhancement (FE) by a factor of 12 ± 1 independently of the pH value and a high Ba2+ sensitivity with a limit of detection (LOD) of (17.2 ± 0.3) µM. Moreover, a second fluorescent probe consisting of the same BODIPY fluorophore, but a benzo‐18‐crown‐6 as a cation‐responsive binding moiety, showed an even higher FE upon Ba2+ complexation by a factor of 85 ± 3 and a lower LOD of (13 ± 3) µM albeit a lower Ba2+ selectivity. The fluorescence sensing mechanism of Ba2+ was further investigated by time‐resolved fluorescence as well as transient absorption spectroscopy (TAS) and it turned out that within these probes a blocking of a photoinduced electron transfer (PET) by Ba2+ is very likely responsible for the FE.