Helicene-Based Chiral Macrocycle: Efficient Synthesis, Spontaneous Chiral Resolution, and Strong Circularly Polarized Luminescence

Abstract

CCS Chemistry, Ahead of Print.
Herein, we report the synthesis of a novel helicene-based chiral macrocycle featuring distinctive conglomerate crystallization and markedly enhanced photophysical and chiroptical properties. Chiral macrocycle 1, consisting of three helicene moieties, is efficiently constructed via Yamamoto coupling of a newly synthesized dichloro-[5]helicene 2. Notably, 1 predominantly adopted the PPM/MMP conformation rather than the more stable PPP/MMM. The structures of both macrocycle 1 and its precursor helicene 2 were unambiguously confirmed by single-crystal X-ray diffraction (XRD). Interestingly, an unusual spontaneous chiral resolution phenomenon was observed upon crystallization of 1, resulting in enantiomerically pure chiral crystals of 1-PPM and 1-MMP. Compared with helicene 2, the absorption of macrocycle 1 was significantly redshifted, and its molar extinction coefficient (ε), as well as the fluorescence quantum efficiency (ΦF), were also remarkably enhanced. Notably, 1 exhibited a superior luminescent asymmetry factor (|glum| = 2.85 × 10−2) and a very high circularly polarized luminescence (CPL) brightness (Bcpl = 1514 M−1 cm−1), which represents one of the best CPL performances among chiral organic molecules. We believe this work provides valuable insights and new perspectives for exploring novel helicene-based macrocycles with multiple conformations, enhanced (chir)optical properties, as well as valuable electronic and optoelectronic applications.