Fluorescent, CPL-Active Azahelicenes in Two Steps
Facile Two-Step Synthesis of 1,10-Phenanthroline-Derived Polyazahelicenes with High Fluorescence and CPL Efficiency.
Angew. Chem. Int. Ed. 2017;
16 May 2017 (online)
Helicenes are molecules comprised of ortho-fused aromatic rings. They have potential applications in circularly polarized luminescence (CPL) emitting materials because some helicenes show high CPL activities. However, the fluorescence quantum yields of helicenes are generally low because the inherent curved π-systems promote rapid intersystem crossing from the singlet to the triplet states. Herein, Shibata and co-workers report a series of azahelicenes that possess both high fluorescence and CPL activity, which make these molecules an appealing CPL-emitting material.
The authors report a facile two-step synthesis of azahelicenes. The quantum yield of 1a (0.39) was comparable to the highest value among reported helicenes (0.40). The addition of acid enhanced the quantum yield of 1a to 0.80. Although the value of the luminescence dissymmetry ratio g lum of 1a decreases slightly upon addition of acid (0.009 at 473 nm to 0.008 at 514 nm), this molecule remains an attractive CPL-emitting material. Single-crystal X-ray analysis and DFT calculations on 1a were also conducted.