Two 3D fsc-type hydrogen-bonded networks as luminescent sensors for turn-on sensing of tryptophan and aspartic acid

Two new luminescent coordination polymers (CPs), [M(Aze)(bmbp)]n (M = Zn for 1; Cd for 2), based on 4,4′-bis(2-methylimidazol-1-ylmethyl)biphenyl (bmbp) and azelaic acid (H2Aze) ligands have been hydrothermally synthesized. In their crystal structures, the metal centers are connected by bmbp and Aze2- to generate 1D chains, which are further linked by CH···O hydrogen bonds to form 3D supramolecular structures. Topological analysis suggests that the 3D hydrogen-bonded networks are binodal (4,6)-connected fsc nets with the symbol of (44·610·8) (44.62). CPs 1 and 2 both dispay excellent photoluminescence with good stability. Luminescent sensing experiments show that both 1 and 2 can be used as turn-on sensors to detect tryptophan (Trp) and aspartic acid (Asp) in aqueous solution. The limits of detections (LODs) toward Trp and Asp are 0.30 and 5.33 μM for 1, 0.23 and 2.62 μM for 2, respectively. Furthermore, the sensing mechanisms were also investigated in detail via various detection means and theoretical calculations. The test films of both CPs were also prepared for visual detection of Trp and Asp.