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

Abstract

Abstract Herein, we report on highly Ba 2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo‐21‐crown‐7 as a Ba 2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba 2+ induced fluorescence enhancement (FE) by a factor of 12±1 independently of the pH value and a high Ba 2+ 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 Ba 2+ complexation by a factor of 85±3 and a lower LOD of (13±3) μM albeit a lower Ba 2+ selectivity. The fluorescence sensing mechanism of Ba 2+ 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 Ba 2+ is very likely responsible for the FE.