AIE -active TPA modified Schiff base for successive sensing of Cu 2+ and His via an on-off-on method and its application in bioimaging.

In this article, a novel triphenylamine-modified salicylaldehyde Schiff base 2-(((4-(diphenylamino)phenyl)imino)methyl)-4-(pyridine-4-yl)phenol (HL) was synthesized and structurally characterized. HL possessed D-π-A structure and exhibited typical AIE property in THF/H 2 O. It was applied to selectively recognize Cu 2+ through an on-off mode in THF/H 2 O (1/9, v/v), and the fluorescence attenuation was attributed to a paramagnetic quenching effect of Cu 2+ together with the abatement of HL aggregates. Hence, the detection limit achieved was as low as 1.32 × 10 -7 M. The spectroscopic and ESI-HRMS results revealed a 1 : 2 complexation ratio of Cu 2+ with HL. The mechanism for sensing Cu 2+ was further confirmed by performing DFT calculations. Owing to the large affinity between Cu 2+ and His, the resultant CuL2 system was further used to detect His via the off-on method based on the displacement of ligands. The detection limit for His reached 5.14 × 10 -8 M. Furthermore, HL was available to prepare handy indicator papers for the on-site recognition of Cu 2+ and His. Confocal fluorescent imaging demonstrated that HL could sequentially respond to intracellular Cu 2+ and His.