A novel fluorescence sensor for K+ based on bis-Bodipy: The ACQ effect controlled by cation complexation of pseudo crown ether ring

Three novel bis-Bodipy 3a–3c bridged with crown ether chain were prepared in yields of 70–78%. Their complexation absorption and fluorescent spectra for fourteen metal ions suggested that compound 3b exhibited the selective response for K⁺ with obvious ACQ effect. The association constant of compound 3b with K⁺ was 4.3 × 10⁵ M^?1 and 1:1 complex mode was deduced. The complexation mechanism of ACQ effect controlled by cation complexation of pseudo crown ether ring was confirmed by the fluorescent titrations, complexation FT-IR spectra, complexation ¹H NMR spectra, complexation ESI-MS spectra and contrast experiment of similar mono-Bodipy derivative. The K⁺ was binded in the cavity of a pseudo crown ether ring, leading to the closed distance for two Bodipy units and then enhancing the ACQ effect obviously. Both the structure of the crown ether chain and two Bodipy units were decisive factors for the selective fluorescence sensor for K⁺.