Turn-On Fluorescence Enantioselective Sensing of Hydroxyl Carboxylic Enantiomers by Metal–Organic Framework Nanosheets with a Homochiral Tetracarboxylate of Cyclohexane Diamide

Two-dimensional
(2D) metal–organic frameworks (MOFs) have
attracted growing interest due to excellent performance in gas separation,
energy conversion and storage, catalysis, and sensing, but their homochirality
and exfoliation as well as related enantioselective catalysis and
sensing remain a stage of pending exploration owing to the scarcity
of homochiral MOFs and intrinsic aggregation of nanosheets. Herein,
a homochiral 2D MOF (HMOF-3) with polymeric chirality, good thermostability,
and solvent stability is designed and constructed by a homochiral
organic ligand 5,5′-((1R,2R)-cyclohexane dicarbonyl bis­(azanediyl)) diisophthalic acid (R,R-CHCAIP), a ditopic coligand 4,4′-bipyridine,
and Zn salts. Remarkably, HMOF-3 can be exfoliated via solvent-assisted
sonication to achieve 2D HMOF-3 nanosheets (HMOF-3-NS), which exhibit
a sensitive turn-on effect with the fluorescence enhancement up to
63.5 times in the presence of R/S-mandelic acid, d/l-tartaric acid, d/l-lactic acid, d/l-alanine, and d/l-tryptophan. More importantly, the high surface area,
polymeric chirality environment, and highly accessible functional
sites on the surface of HMOF-3 nanosheets enable close contact with
probed enantiomers, leading to highly enantioselective and sensitive
sensing. The turn-on mechanism of host–guest-assisted electronic
transfer is confirmed by DFT calculation and the relative experiment.
This work highlights the promise of homochiral 2D MOF nanosheets for
enantioselective sensing applications.