Novel symmetric Schiff-base benzobisthiazole-salicylidene derivative with fluorescence turn-on behavior for detecting Pb2+ ion

A novel ligand, N2 ,N6 -bis(2-salicylidene)benzobisthiazole (BSBBT), was designed and synthesized with an excellent yield through a facile one-step condensation eco-reaction for fluorescent detection of Pb2+ ions. BSBBT was well-characterized through FT-IR, 1 H NMR, 13C NMR and XRD for inclusive study of photo-physical behaviors. From the value of aggregation induced enhanced emission (AIEE) and excited-state intramolecular proton transfer (ESIPT) properties with a large Stocks shift (160 nm), BSBBT was characterized highly emissive in DMSO/H2O (30:70, v/v) solution as well as in solid-state. BSBBT showed a strong fast response and highly selective and sensitive “turn-on” fluorescent sensing behavior for detecting Pb2+ ions in phosphate buffer solution (PBS) without any interference from other metal cations at the physiological pH (∼7.4). The calculated binding constant and detection limit were 0.41 × 105 M−1 and 2.23 × 10-6 M, respectively. Density Functional Theory calculation confirmed the formation of stable BSBBT-Pb2+ complex with a lower energy gap compared to BSBBT. BSBBT is the first high-efficient luminescent benzobisthiazole-base fluorescent sensor reported so far for detecting Pb2+ ions in PBS at the physiological pH range