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

Abstract

Comprehensive SummaryThe 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 × 10‐2 and +9.2 × 10–3, respectively. This work provides the useful evidences to reveal the induced chiral crystallization and the construction of CPL‐active crystalline materials.

Chiral Coordination Assembly-Induced Phosphorescent Frameworks for Circularly Polarized Phosphorescence

“…Chiral coordination assembly has been demonstrated to be a potential approach to prepare long-lived chiral crystalline frameworks, which can transfer chirality to achiral phosphorescent ligands − and suppress the nonradiative decay of triplet excitons, resulting in the enhancement of the spin–orbit coupling and quantum yield. , …”

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

“…36–38 Nevertheless, these multi-component systems mainly belong to the category of soft materials, their aging and deformation can affect the stability of chiral structures, and they are often unable to provide accurate aggregation structures to reveal the generation, transfer and amplification of chirality. 39–41…”

Circularly Polarized Luminescence of Tetradentate-Ligand-Based Chiral MOFs: Structural Evidence of Chirality Inversion

“…In order to shed light on this topic, different coordination assemblies were prepared by varying the stoichiometry of d -cam and TPPE. In addition, it remains a huge challenge to determine the absolute homochirality of the bulk sample because of the difficulty of obtaining each crystal by X-ray diffraction analysis. , We systematically isolated 16 single crystals corresponding to each different molar ratio of the coassembly and carried out X-ray diffraction analysis. All the structures of the 16 randomly isolated single crystals corresponding to the d -cam:TPPE molar ratio 2:1 belonged to the space group P 6 2 22, thereby highlighting the homochirality of the system.…”