Enhanced Enantioselective Sensing of 1,1′-Bi-2-naphthol and Mandelic Acid by Proportional Fluorescence Sensor 3DOM Zn-MOF-74-l-Trp with Hierarchical Macro–Micropore Structure

Abstract

The enantioselective performance of porous chiral metal–organic frameworks (CMOFs) is closely related to the pore size and uniformity of easily accessible active sites. The chiral recognition efficiency of microporous CMOFs is hindered by the restricted diffusion of the guest. Hierarchical porous chiral CMOFs with multiple pore size regimes ranging from micropores to macropores have emerged as potential candidates in chiral separation applications. 3DOM Zn-MOF-74 crystalline porous material with ordered macro–micropore structure was prepared with a general bottom-up strategy by carrying out the controllable confined growth of Zn-MOF-74 precursor in a removable three-dimensional ordered macroporous (3DOM) polystyrene (PS) template. Then l-tryptophan ( l -Trp) was introduced into MOFs by the strategy of postsynthetic modifications, and finally, a chiral hierarchical porous functional material 3DOM Zn-MOF-74-l-Trp was successfully fabricated. Based on the two luminescent centers from the achiral ligand H₄DOBC and chiral ligand l-Trp, the proportional fluorescence sensor 3DOM Zn-MOF-74-l-Trp was hopeful to be applied in the field of enantioselective fluorescence sensing. The enantioselectivity factor values of microporous M-Zn-MOF-74-l-Trp for 1,1′-bi-2-naphthol (Binol) and mandelic acid (MA) were 1.08 and 1.12, respectively. In comparison, the construction of hierarchical porous structure greatly enhanced the chiral recognition performance, which may be due to the improved mass-transfer efficiency of chiral guest molecules and highly swelled accessibility to the chiral recognition sites in this CMOF composite, making the enantioselectivity factor values correspondingly increased to 1.29 and 2.26, respectively.