A multi-responsive luminescent Co(ii) coordination polymer assembled from amide-functionalized organic units for effective pH and cation sensing

Abstract

By employing an amide-containing multicarboxylate ligand of N,N′′-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H₄L), a 3D (3,4,4,6)-connected Co(II) coordination polymer, namely, [Co(L)_0.5(tttmb)(H₂O)]_n (LCU-112, LCU = Liaocheng University, tttmb = 1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene) has been constructed through solvothermal synthesis. LCU-112 demonstrates a novel (3,4,4,6)-connected {4².6}₂{4².8³.10}{4².8⁴}{4⁴.6².8⁷.10²} net. Fluorescence measurements reveal that LCU-112 could display a highly sensitive fluorescence response to different pH systems, especially in the pH range from 3.93 to 4.46. It may also be viewed as a recyclable on-off-on vapoluminescent sensor responding to typical acidic and alkaline gases HCl and Et₃N. Remarkably, it exhibits excellent turn-on/ratiometric fluorescence sensing ability toward Pb²⁺ and Al³⁺ with a detection limit as low as 0.075 and 0.759 μM, respectively. LCU-112 also has a good fluorescence recognition function on Tb³⁺ with a detection limit of 0.046 μM. Specially, Pb²⁺ and Al³⁺ ions can be further distinguished in the presence of Tb³⁺. For practical application, luminescent test papers for the detection of the above ions in tap water samples were designed. Furthermore, visualization of the quenching effect on Fe³⁺ could also be improved by replacing LCU-112 with the post-synthesized sample Tb³⁺@LCU-112. As a result, this Co-based coordination polymer could be explored as a multifunctional fluorescent material for environmental monitoring.