A new strategy to fabricate multifunctional luminescent MOFs, extending their application range from pH sensing to amino acid information coding

Abstract

Herein, we propose a new strategy for designing new types of wide range pH-sensitive metal-organic frameworks (MOFs) with double luminescent centers on UiO-66-2OH. The UiO-66-2OH has a ligands-based emission at 530 nm. To introduce another luminescent center, PMA (1,2,4,5-benzenetetracarboxylic acid), as the functional site, is used to substitute the initial ligand, BDC-2OH (2,5-dihydroxyterephthalic acid), of UiO-66-2OH. Eu3+ ions, another luminescent center at 613 nm, are coordinated to the free carboxyl group on PMA. Finally, TTA (2-Thenoyltrifluoroacetone) is coordinated with Eu3+ ions to balance the emission at 613 nm (Eu3+ ions) and 530 nm (BDC-2OH). For the sake of both strong emissions, we explored the loading levels of PMA. The optimized structure is Eu(TTA)@MUM5 (“MUM” is the abbreviation of “Mixed ligand UiO-66-2OH MOFs” and “5” represents the molar percentage of PMA is 50%), which exhibits strong emission at 530 nm (alkaline solution) and 613 nm (neutral solution). Remarkably, the synthesized material has an exponential relationship (R2 = 0.9973) over the pH range of 1.87 to 9.65 and a linear relationship (R2 = 0.9987) when pH = 11.01–13.35. Further experiments have proved that Eu(TTA)@MUM5 could distinguish different amino acids. Based on that, we build an information transferring circle with two coding modes on Eu(TTA)@MUM5 using aseptic acid and arginine as coding factors.