A luminescent coordination polymer constructed from a fluorene-based bifunctional ligand for the selective detection of tetracyclines and 2,4,6-trinitrophenol

Abstract

Taking simple fluorene as a starting material, a new flexible bifunctional “+” shape ligand H₂L was synthesized in high yield through bromination, Michael addition, and Ullmann and hydrolysis reactions. Two new coordination polymers [CdL·3H₂O]_n (CP–Cd) and [PbL·H₂O]_n (CP–Pb) were synthesized with combined advantages of two functional groups (carboxyl and imidazolyl groups) under solvothermal conditions. Crystal structure analysis shows that CP–Cd and CP–Pb are isomorphous and have a two-dimensional (2D) framework with a single-node SP 2-periodic net (6,3)Ia topology. Moreover, CP–Cd could selectively detect two antibiotics (TC: tetracycline; CTC: chlortetracycline) in an aqueous solution with high selectivity and sensitivity through a turn-off effect, and also shows high efficiency in fluorescence quenching toward 2,4,6-trinitrophenol (TNP) detection. The detection limits are 0.103 μM (TC), 0.098 μM (CTC) and 0.147 μM (TNP), respectively. Also, the rational mechanism of fluorescence sensing was also discussed in detail by experiments and theoretical calculation, which revealed that competitive absorption (CA), fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) largely contribute to the sensing of TNP and the two antibiotics.