An efficient ICT based fluorescent turn-on dyad for selective detection of fluoride and carbon dioxide

Abstract

A new intramolecular charge transfer (ICT) based fluorescent turn-on ratiometric probe 2 (D–π–A type) has been designed and synthesized by bridging imidazole (donor, D) and benzothiazole (acceptor, A) moieties through a phenyl ring. The photophysical behavior of probe 2 in solvents of different polarities and at different pH values has been investigated. Upon interaction with different types of anions probe 2 showed selective high affinity for fluoride anions (F⁻) in aqueous DMSO (20%) solution. The ratiometric fluorescence turn-on behavior displayed by 2 with F⁻ is attributed to changes in the ICT process. Job's plot analysis revealed a 1 : 1 binding stoichiometry for 2 + F⁻ interactions with a high binding constant and detection sensitivity (30 ppb). Moreover, a solution of 2 + F⁻ enabled the detection of CO₂ (∼100 ppb; 2.29 μM) through enhanced emission. The mode of interaction has been confirmed by ¹H NMR titration studies which suggested the deprotonation of the –NH fragment of an imidazolyl unit in the presence of F⁻.