Charge-Transfer-Induced Morphological Transformation of a Butterfly-Shaped Pyrene-Flanked Chiral Macrocycle

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Materials Science

Background:

• Chiral macrocycles are crucial for developing advanced functional materials.
• Self-assembly of molecular building blocks offers pathways to complex architectures.
• Fluorescent properties and chiroptical responses are key for sensing and optical applications.

Purpose of the Study:

• To design, synthesize, and characterize a novel chiral, fluorescent macrocycle (CFM).
• To investigate the self-assembly behavior of CFM in solution and solid states.
• To explore the chiroptical properties and charge transfer interactions of CFM.

Main Methods:

• Synthesis of pyridine-2,6-dicarboxamide (PDC) based chiral macrocycle.
• Single crystal X-ray diffraction (SCXRD) for structural elucidation.
• UV-Vis absorption, Circular Dichroism (CD), and Circular Polarized Luminescence (CPL) spectroscopy.
• Morphological studies using microscopy.
• Charge Transfer Interaction (CTI) studies with tetracyanobenzene (TCNB).

Main Results:

• CFM adopts a rigid, helically twisted conformation stabilized by intramolecular H-bonding.
• CFM self-assembles into twisted ribbons whose helical direction depends on molecular chirality.
• Ribbon assemblies exhibit enhanced CD and CPL signals (g_lum up to 7 × 10^-3).
• CTI with TCNB induces red-shifted chiroptical signals and a morphological transition to microspheres.
• CT coassemblies display CPL in the orange-red region (g_lum 3 × 10^-4).

Conclusions:

• The synthesized CFM is a versatile building block for chiral supramolecular assemblies.
• Molecular chirality dictates the self-assembly pathway and chiroptical properties.
• Charge transfer interactions offer a method to tune the morphology and optical output of CFM assemblies.
• These findings open avenues for developing novel chiroptical materials for sensing and photonics.