Exploiting aggregation induced emission and twisted intramolecular charge transfer in a BODIPY dye for selective sensing of fluoride in aqueous medium and living cells

A novel red fluorescent probe based on boron dipyrromethene (BODIPY) was successfully designed and synthesized, consisting of electron acceptor 1,3,5,7-tetramethyl-8-phenyl-BODIPY (BDP) and electron donor triphenylamine (TPA) units using Suzuki cross-coupling methods TPA-BDP exploits the advantages of both aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT). An X-ray crystal structure of TPA-BDP reveals a network of CH⋯F intermolecular interactions which can contribute to rigidifying the molecular conformation. Thereby, aggregation restricts the intramolecular rotation associated with the donor moiety, inducing a great enhancement in the emission efficiency. This new dye features high sensitivity and excellent selectivity to fluoride ions with a detection limit of 0.73 μM in aqueous medium. The sensing mechanism was systematically investigated by 1H NMR, 19F NMR, 11B NMR and mass spectrometry. It is proposed that fluoride reacts in a nucleophilic displacement reaction at the BDP core which disrupts the structure of TPA-BDP, thereby causing the red fluorescence of TPA-BDP quenched. It is noteworthy that TPA-BDP has been utilized for the fluorescence imaging and fluoride ions detection in living cells with very low cytotoxicity.