Red Emissive Double Aza[7]helicenes with Antiaromaticity/Aromaticity Switching via the Redox-Induced Radical Cation and Dication Species.

Abstract

We herein present the synthetic approach to a new antiaromatic double aza[7]helicene C that features NN-embedded polycyclic aromatic hydrocarbons (PAHs). This heteroatom-doped helicene showed a rarely obtained long-wavelength emission and far- red circularly polarized luminescence (CPL) in the solid state. These optical and chiroptical properties could be ascribed to both the NN-PAH core structure and the further extension via angular ring fusions. Such a unique electronic structure also culminated in facile chemical oxidations of neutral C to the positively charged chiral radical (C•+) and dication species (C2+). Interestingly, DFT computations revealed that the pyridazine central core showed an antiaromaticity-to-aromaticity switching, in contrast to the inversed transition for the helical periphery in cationic states. The reported approaches are anticipated to further develop redox-active chiral systems for potential applications in chiroptoelectronics, spintronics as well as fluorescent bioimaging.