Multiresponsive luminescent sensors for antibiotics and Cr^VI with two luminescent Zn^II/Cd^II coordination complexes

Two new Zn^II/Cd^II luminescent coordination polymers (CPs) based on the V-shaped bis(imidazole) ligand 3,6-bis (1H-benzo[d]imidazol-1-yl)-9-methyl-9H-carbazole (bbimc) with [1,1'-biphenyl]-4,4'-dicarboxylic acid ligand (H₂bpdc) have been synthesized under solvothermal conditions: {[Zn(bbimc)(bpdc)]·DMF·2.5H₂O} (CP 1), {[Cd(bbimc)(bpdc)]·2DMF} (CP 2). CP 1 and CP 2 both display a uninodal 4-c unimodal sql topology 2D framework with vertex symbols of {4⁴·6²}. In addition, the two identical 2D nets of CP 2 were interpenetrated each other to form a 2D + 2D → 3D and generate a 2-fold interpenetrating architecture. Moreover, sensing investigations of CP 1 and CP 2 revealed that both of compounds can be used as a highly sensitive and selective multi-responsive luminescent sensor for sensing Cr₂O₇^2-, CrO₄^2- and antibiotics (TC: Tetracycline; CTC: Chlortetracycline) in H₂O by exhibiting fluorescence quenching with significant quenching constants (K_sv = 1.369 × 10⁴ M^-1 (Cr₂O₇^2-), 2.003 × 10⁴ M^-1 (CrO₄^2-), 5.343 × 10⁴ M^-1 (TC), 8.706 × 10⁴ M^-1 (CTC) for CP 1 and 4.452 × 10⁴ M^-1 (Cr₂O₇^2-), 2.119 × 10⁴ M^-1 (CrO₄^2-), 4.175 × 10⁴ M^-1 (TC), 1.257 × 10⁵ M^-1 (CTC) for CP 2). The detection limit are 0.67 μM (Cr₂O₇^2-), 0.48 μM (Cr₂O₇^2-), 0.23 μM (TC), 0.14 μM (CTC) for CP 1 and 0.28 μM (Cr₂O₇^2-), 0.54 μM (CrO₄^2-), 0.31 μM (TC), 0.098 μM (CTC) for CP 2, respectively. In addition, the probable fluorescence quenching mechanism was studied through experiment and theoretical calculation and the co-existance of competitive absorption (CA) and photoinduced electron transfer (PET) progress contributed to such sensing processes.