Functionalized BODIPY with various sensory units – a versatile colorimetric and luminescent probe for pH and ions

Abstract

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives containing ion- and pH-sensory units have been successfully designed and synthesized. One of the compounds was structurally characterized by X-ray crystallography. Owing to the presence of an ICT absorption band, one of the compounds was found to show pronounced solvatochromic behavior in different organic solvents. Their emission energies in various solvents show a linear dependence on the Lippert solvent parameter. The cation-binding properties of the complexes with different metal ions (alkali metal, alkaline earth metal and transition metal ions) have been studied using UV-vis and emission spectroscopies. A 1 : 1 complexation to metal ions (Li⁺, Na⁺, Mg²⁺, Ba²⁺, Zn²⁺, Cd²⁺) was found for the compound with one azacrown moiety in acetonitrile while another one with two azacrown moieties was shown to form 1 : 2 complexes with Zn²⁺ and Mg²⁺ cations. Their stability constants have been determined by both UV-vis and emission spectrophotometric methods. By introducing triarylborane moieties into the meso position and the 2-position of the BODIPY skeleton, different electronic absorption spectral changes together with an emission diminution were observed in response to fluoride ions. Ditopic binding study of 5, which was functionalized with both azacrown and triarylborane moieties, showed emission enhancement in the presence of Mg²⁺ and F⁻. These findings suggest that these BODIPY derivatives are capable of serving as versatile colorimetric and luminescence probes for pH, cations and F⁻.