Tether-entangled conjugated helices.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Helical polyaromatic molecules are of interest for their unique electronic and optical properties.
• Achieving stable and tunable helical structures with controlled chirality remains a challenge.

Purpose of the Study:

• To introduce a new design concept, tether-entangled conjugated helices (TECHs), for creating helical polyaromatic molecules.
• To demonstrate the customizable synthesis and persistent chiral properties of TECHs.
• To investigate the photophysical properties, including circularly polarized luminescence (CPL), of TECHs.

Main Methods:

• Modular synthesis utilizing planar chiral tethering units (C2 symmetry) and docking units (C2h symmetry).
• Characterization of synthesized concave-type and convex-type TECHs.
• Single-crystal X-ray diffraction analysis.
• Theoretical studies on π-dimer formation and binding energies.
• Photophysical measurements, including concentration-dependent emission and CPL spectroscopy.

Main Results:

• Successful synthesis of TECHs with determinate helical chirality and persistent properties without post-chiral resolution.
• Observation of unconventional double-helix π-dimers in concave-type TECHs, with lower binding energies than planar π-dimers.
• Exhibition of concentration-dependent emission in concave-type TECHs, attributed to excited-state double-helix π-dimer formation.
• All TECHs demonstrated strong CPL, with |g_lum| generally exceeding 10⁻³.
• The (P)-T4-tBu derivative achieved a high |g_lum| of 1.0 × 10⁻² and a CPL brightness of 316 M⁻¹ cm⁻¹.

Conclusions:

• TECHs provide a versatile platform for designing molecules with tunable 3D helical structures and inherent chirality.
• The covalent locking by tethers ensures persistent chiral properties.
• TECHs exhibit promising CPL characteristics, making them potential candidates for advanced optical applications.