Two 3D Ni(II) Coordination Polymers as Luminescent Sensors for Turn-Off Sensing of Uric Acid And Turn-On Sensing of Tryptophan

Two new three-dimensional (3D) Ni(II) coordination polymers (CPs), namely, {[Ni(L1)₂(H₂O)₂]·(1,5-NDS)}_n (1) and [Ni(L2)₂(1,5-NDS)]_n (2) have been hydrothermally synthesized based on 1,5-naphthalenedisulfonate (1,5-NDS) and two bis(benzimidazole) ligands (L1 = 1,4-bis(1H-benzimidazol-1-yl)butane, L2 = 1,2-bis(benzimidazol-1-ylmethyl)benzene). CP 1 presents a 3D framework with 4-connected 6⁶ dia topology. While CP 2 shows a 3D network with 6-connected (4¹².6³) pcu topology. CPs 1 and 2 both exhibit excellent luminescent properties and good water stability. And luminescent sensing experiments reveal that both CPs can detect uric acid (UA) in aqueous solution through the luminescent quenching effect, and they also can detect tryptophan (Trp) in aqueous solution with red-shift and turn-on luminescent effect. The detection limits toward UA and Trp are 1.30 and 0.92 μM for 1, and those are 1.20 and 1.30 μM for 2, respectively. Furthermore, the luminescence sensing mechanisms were studied via PXRD patterns, UV–Vis spectra, lifetimes and theoretical calculations. The luminescence test films of 1 and 2 were also prepared for visual detection of UA and Trp.