Turn-on fluorescent naphthalimide-benzothiazole probe for cyanide detection and its two-mode aggregation-induced emission behavior

Naphthalimide-benzothiazole conjugate (NBTZ) linked by cinnamonitrile was designed, synthesized, and fully characterized by NMR (H-1, C-13, DEPT, HSQC) and high-resolution mass spectrometry. NBTZ exhibited unique turn-on fluorescence in the presence of CN- with relatively high selectivity compared to other anions such as SCN-, HSO4-, ClO4-, NO3-, Cl-, Br-, I-, and PO4-3 in tetrahydrofuran (THF). The detection limit for CN- was found to be 3.35 x 10(-8) M in THF. The sensing mechanism was analyzed through H-1, C-13, DEPT, and mass spectroscopy. NBTZ also showed two-mode aggregation-induced emission (AIE) in THF-H2O mixtures. In a 30:70 THF-H2O (v/v) mixture, the maximum AIE was observed at 430 nm (blue) because of the rotation of the C-C bond between the naphthalimide ring and the phenyl ring was restricted. In 10:90 THF-H2O (v/v), a new red-shifted AIE appeared at 490 nm (cyan), due to the extended pi-conjugation induced by restriction of rotation of the C=C bond between the benzothiazole and naphthalimide rings. (C) 2021 Elsevier B.V. All rights reserved.