Layer-By-Layer Chiral Induction of Fluorene-Based Metal-Organic Framework Films for Circularly Polarized Luminescence Sensing of Enantiomers

Developing films of chiral metal-organic frameworks (MOFs) with high circular polarization luminescence (CPL) is facing a great challenge for chiral sensing applications. Herein, a layer-by-layer chiral induction method is first reported to prepare enantiopure MOF films for CPL sensing. By layer-by-layer induction with the chiral inductor camphorsulfonic acid, fluorene-based chiral MOF D/L-ZnHF-SO2 film (HF-SO2 = 3,7-Dibenzothiophenedicarboxylate, 5,5-dioxide) with preferential growth orientation and homogeneous surface are prepared, which shows strong chiral feature and CPL with higher asymmetry factor of +/- 0.073. In addition, by mixed ligand approach, the isostructural fluorene ligand 9-fluororenone-2,7-dicarboxylate is chosen to replace part of HF-SO2 for preparing a series of chiral MOF films with tunable CPL emission. Furthermore, the prepared chiral MOF films with strong CPL performance are further utilized for enantiomers sensing. The CPL changes consisted with enantioselective adsorption results showed that D/L-ZnHF-SO2 film has good discrimination against chiral R/S-phenylethylamine enantiomers, first reporting chiral MOF-based candidates for the application in CPL sensing of enantiomers. This work provides a facile and effective approach for preparing chiral MOF films materials with high and tunable CPL performance, and also gives a new way to achieve CPL sensing of chiral enantiomers.