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

Herein we report the design, synthesis, and self-assembly behaviour of a chiral, fluorescent macrocycle (CFM) based on a pyridine-2,6-dicarboxamide (PDC) core, incorporating cyclohexane-1,2-diamine as a chiral linker. Single crystal x-ray diffraction (SCXRD) structural analysis confirmed that CFM adopts a rigid helically twisted conformation stabilized through intramolecular H-bonding. The CFM self-assembled into twisted-ribbons in 50% DMF/water mixture. The helical-twist direction of these ribbons was governed by the molecular chirality of the enantiomeric macrocycles (R,R)-CFM and (S,S)-CFM. These ribbon-shaped assemblies displayed increased circular dichroism (CD) and circular polarized luminescence (CPL) signal with g_lum up to 7 × 10^-3 at λ = 490 nm. Furthermore, CFM showed charge transfer interaction (CTI) with tetracyanobenzene (TCNB), resulting in distinct red-shifted chiroptical signals in both the solution and the solid states. The formation of the CT complex induced a distinct morphological transition, disrupting the twisted ribbon structures and yielding microspheres at higher ratios of TCNB. Remarkably, the CT coassembly exhibited CPL in the orange-reddish region with g_lum 3 × 10^-4 at λ = 650 nm. SCXRD further revealed that TCNB molecules were intercalated between the pyrene wings of two CFM molecules, stabilized through strong intermolecular interactions such as π-π stacking and C─H···O interactions with the amide oxygen.