Nanoaggregation‐Enhanced and Inverted Circularly Polarized Luminescence in Isomeric Schiff Base Bis(boron difluoride) Complexes

Chiral V-shaped Schiff base molecules with positional isomerism were designed. Coordination with boron difluoride (BF₂) activated circularly polarized luminescence (CPL). Subsequent supramolecular nanoaggregation enabled precise CPL modulation. Notably, the two positional isomers exhibited starkly different chiroptical properties upon aggregation.

Abstract

To elucidate the emergence and amplification of circularly polarized luminescence (CPL) in chiral molecules and their assemblies, we designed positionally isomeric chiral V-shaped Schiff base ligands and their corresponding bis(boron difluoride) complexes. The ligands were synthesized by condensing chiral cyclohexanediamine with either 1-hydroxy-2-naphthaldehyde or 2-hydroxy-1-naphthaldehyde, followed by complexation with boron difluoride (BF₂) to yield CNB1 and CNB2, respectively. While the parent Schiff bases exhibited no CPL, BF₂ coordination induced strong CPL signals in solution. Remarkably, upon aggregation in a mixed solvent system, CNB2 displayed enhanced and inverted CPL, whereas its isomer CNB1 showed attenuated emission. Through comprehensive characterization and singlecrystal analysis, we attribute this divergent behavior to distinct molecular packing modes: CNB2 forms tightly stacked aggregates with efficient π─π interactions, while CNB1 adopts a less ordered arrangement. This study establishes a clear correlation between subtle structural modifications, supramolecular packing, and CPL performance, offering a rational strategy for tailoring chiroptical properties through precise molecular design and controlled self-assembly.

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