An α-benzithiazolyl 3-pyrrolyl BODIPY probe for ratiometric selective sensing of cyanide ions and bioimaging studies

Abstract

A simple chromo-fluorogenic chemodosimeter probe, α-benzithiazolyl 3-pyrrolyl BODIPY, was synthesized by reacting α-formyl 3-pyrrolyl BODIPY with 2-aminothiophenol in DMF at reflux under basic conditions. The probe was structurally characterized by X-ray, HR-MS, and 1D & 2D NMR techniques. The X-ray structure revealed that the appended pyrrole was almost in the plane with a small deviation of 12.15° from the 12-atom mean plane of the BF₂-dipyrrin core and the benzithiazolyl moiety was also deviated by 18.74° from the BF₂-dipyrrin core. The α-benzithiazolyl 3-pyrrolyl BODIPY exhibits one intense absorption band at 608 nm and a less intense band at 412 nm corresponding to the 3-pyrrolyl BODIPY and benzithiazolyl moiety, respectively. The strongly fluorescent probe shows one intense emission band at 637 nm with a quantum yield of 0.48. The probe acted as an exclusive colorimetric and chemodosimetric sensor for CN⁻ ions over other anions with high sensitivity (LOD = 13 nM) and quick response time (10 s) in an aqueous CH₃CN medium. The CN⁻ ion attacks the imine group of the benzithiazolyl moiety of 3via a nucleophilic addition reaction and converts the sp² to sp³ carbon which disrupts the conjugation between the 3-pyrrolyl BODIPY and benzithiazolyl moieties, which is reflected in the clear colour change from red fluorescence to blue fluorescence as well as significant changes in the spectral and electrochemical properties. The detection of cyanide with the probe for biological applications was also performed with plant tissue. DFT/TD-DFT studies were in agreement with the experimental observations.