Synthesis and self-aggregation of cyclic alkynes containing helicene

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Helicenes are chiral aromatic compounds with unique three-dimensional structures.
• Cyclic alkynes offer rigid scaffolds for constructing complex molecular architectures.
• Self-aggregation in solution is a key phenomenon in supramolecular chemistry and materials design.

Purpose of the Study:

• To synthesize all stereoisomers of a novel cyclic alkyne containing three helicene units.
• To investigate the self-aggregation behavior of these stereoisomers in organic solvents.
• To elucidate the influence of helicene chirality on molecular self-assembly.

Main Methods:

• Synthesis of 1,12-dimethylbenzo[c]phenanthrene-based cyclic alkynes.
• Vapor pressure osmometry to determine aggregation states and concentrations.
• Solvent-dependent aggregation studies in chloroform and benzene.

Main Results:

• Successful synthesis of all stereoisomers of the target cyclic alkyne.
• (M,M,M)-[3 + 3]cycloalkynes form dimers in solution above 2 mM, with no higher aggregation observed.
• Diastereomeric (M,P,M)-[3 + 3]cycloalkynes exhibit weaker aggregation, forming dimers only above 15 mM.
• Racemic mixtures show significantly reduced aggregation compared to enantiomerically pure forms.

Conclusions:

• The chirality of helicene units critically influences the self-aggregation of cyclic alkynes.
• Enantiopurity promotes stronger intermolecular interactions and dimer formation.
• Understanding these aggregation behaviors is crucial for designing chiral supramolecular structures and functional materials.