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 Cu2+ and Al3+ detection relayed by PO43−. TFPB-PI(F)–COF serves as a highly sensing platform with the superior selectivity toward Cu2+ and Al3+ based on the coordination interaction and the chelation enhancement quenching (CHEQ) effect, and the detection limits are 2.3 and 4.2 nmol L−1, respectively. Subsequently, accompanied with the gradual introduction of PO43−, TFPB-PI(F)–COF@M (Cu2+ and Al3+) complex is wrecked due to electrostatic attraction with the detection limit of 10 nmol 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 Cu2+ and Al3+ in environmental water samples with recoveries of 96.00–104.63 % and RSD <4.62 %. Moreover, the fluorescent images for the visual detection of Cu2+ is also fabricated in living HeLa cells, which provides a modest contribution and an effective platform to the biological analysis.