Induced Absolute Configuration of Achiral Tetradentate Ligands in Metal-Organic Frameworks for Circularly Polarized Luminescence

The crystallization of chiral molecules is of great significance to understand the origin and evolution of hierarchical chirality and reveal the relationships between structural chirality and circularly polarized luminescence (CPL) activity. Here, we report two pairs of chiral metal-organic frameworks (MOFs) (DCF-17/LCF-17, DCF-18/LCF-18) by utilizing tetradentate ligands tetra(3-imidazoylphenyl)ethylene (TIPE) and 4,4'-[4',5'-bis[4-(4-pyridinyl)phenyl][1,1':2',1"-terphenyl]-4,4"-diyl]bis[pyridine] (TPPP) as linkers. It can be observed that the spontaneous resolution of the achiral ligands is converted into the induced resolution, and the ligands form the absolute configuration by using enantiopure camphoric acid (cam) as chiral induced reagent (CIR). As a result, the racemate MOFs can be driven to generate absolute homochiral crystallization. Another two achiral MOFs [Cd(D-cam)(TPPP)0.5] (AF-1, AF = achiral framework) and [Cd(L-cam)(TPPP)0.5] (AF-2) were prepared. The position disorder of D/L-cam skeleton causes the generation of nonchiralization, further leading to disappearance of symmetry breaking of TPPP. For the perspective of structure, this is the first report which reveals the chiral transfer and nonchiralization between chiral induced agents and tetradentate ligands. Besides, DCF-17 and LCF-17 show CPL with luminescence dissymmetry factor (glum) of -1.0 x 10-2 and +9.2 x 10-3, respectively. This work provides the useful evidences to reveal the induced chiral crystallization and the construction of CPL-active crystalline materials. Chiral induction agent can control the formation of the absolute configuration of racemate ligands. Two pairs of homochiral metal-organic frameworks (MOFs) were synthesized with the presence of enantiopure camphoric acid (D/L-cam). Importantly, DCF-17 and LCF-17 exhibit the efficient circularly polarized luminescent (CPL) activity with a luminescence dissymmetry factor (glum) value of -1.0 x 10-2 and +9.2 x10-3, respectively. image