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

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Chirality plays a crucial role in molecular recognition and optical properties.
• Circularly polarized luminescence (CPL) from chiral molecules is vital for advanced optical applications.
• Controlling CPL in molecular assemblies remains a challenge.

Purpose of the Study:

• To investigate the influence of positional isomerism on CPL in chiral Schiff base ligands and their boron difluoride complexes.
• To understand how molecular structure and aggregation affect CPL emission.
• To establish a rational design strategy for tuning chiroptical properties.

Main Methods:

• Synthesis of positionally isomeric V-shaped Schiff base ligands and their bis(boron difluoride) complexes (CNB1 and CNB2).
• Spectroscopic characterization, including CPL measurements in solution and aggregated states.
• Single-crystal X-ray diffraction to analyze molecular packing and supramolecular structures.

Main Results:

• Parent Schiff bases showed no CPL; BF2 coordination induced strong solution CPL.
• Aggregated CNB2 exhibited enhanced and inverted CPL, while CNB1 showed attenuated emission.
• Distinct packing modes (tightly stacked vs. less ordered) were observed via single-crystal analysis, correlating with CPL behavior.

Conclusions:

• Subtle structural changes in chiral ligands significantly impact CPL properties upon aggregation.
• Molecular packing, particularly π–π interactions, is critical for controlling CPL amplification and inversion.
• This work provides a framework for designing molecules with tailored chiroptical functionalities through precise molecular design and self-assembly.