Dynamic Covalent Platform for Chiroptically Tunable Figure-Eight Macrocycles from Preorganized Alkaloidal Scaffolds

Area of Science:

• Supramolecular Chemistry
• Organic Materials Science
• Chiroptical Materials

Background:

• Chiral D2-symmetric figure-eight macrocycles with extended π-conjugated systems are key scaffolds for advanced chiroptical materials.
• Developing efficient and tunable synthetic routes to these complex structures remains a challenge.

Purpose of the Study:

• To establish a dynamic covalent platform for synthesizing tunable chiral figure-eight macrocycles.
• To explore the relationship between molecular architecture and chiroptical properties.
• To translate natural-product-inspired scaffolds into functional materials.

Main Methods:

• Utilized a preorganized alkaloidal bispyrrolidinoindoline (BPI) scaffold.
• Employed thermodynamically controlled imine formation for macrocyclization.
• Incorporated aryl-ethynyl substituents for scaffold preorganization and chromophore diversity.
• Performed postsynthetic conversion of imine linkages to rigid B-N chelates via boranil formation.

Main Results:

• Achieved highly efficient macrocyclization (up to 81% yield) using reversible imine chemistry.
• Synthesized 44-90 membered macrocycles with predictable optical and chiroptical responses.
• Generated a bright orange emitter with high fluorescence quantum yield (Φfl = 0.54).
• Observed enhanced circularly polarized luminescence (CPL) activity (glum = 1.97 × 10⁻³).

Conclusions:

• Established a general design principle integrating dynamic covalent chemistry and conformational preorganization.
• Demonstrated a modular approach for creating diverse, tunable chiroptical materials.
• Successfully translated natural-product-inspired molecular architecture into functional figure-eight macrocycles.