Multi-responsive fluorescent covalent organic framework based on phenanthro[9,10-d]imidazole moiety for relayed detection of Cu2+/Al3+ followed by PO43− and its applications

Designation and application of the luminescent COFs remains a tough challenge and imperative task because of their limited building block structure, the unavailable raw material, the tedious modification process, or the onefold sensing function. Herein, a fluorinated fluorescent covalent organic framework containing a phenanthro[9,10- d ]imidazole moiety [TFPB-PI(F)–COF] had been successfully designed for Cu 2+ and Al 3+ detection relayed by PO 4 3− . TFPB-PI(F)–COF serves as a highly sensing platform with the superior selectivity toward Cu 2+ and Al 3+ based on the coordination interaction and the chelation enhancement quenching (CHEQ) effect, and the detection limits are 2.3 and 4.2  n mol L −1 , respectively. Subsequently, accompanied with the gradual introduction of PO 4 3− , TFPB-PI(F)–COF@M (Cu 2+ and Al 3+ ) complex is wrecked due to electrostatic attraction with the detection limit of 10  n mol L −1 , led to the fluorescent recovery of TFPB-PI(F)–COF. Furthermore, the reversible fluorescent performance by the mode of “on–off–on” is perfect. Besides, the established relayed method can be successfully employed for the analysis of Cu 2+ and Al 3+ in environmental water samples with recoveries of 96.00–104.63 % and RSD <4.62 %. Moreover, the fluorescent images for the visual detection of Cu 2+ is also fabricated in living HeLa cells, which provides a modest contribution and an effective platform to the biological analysis.