Crystallization-Induced Planar Chirality by Asymmetric Ferrocene-Appended Tetraazanaphthacene

Although highly challenging, spontaneous crystallization without racemization can be an innovative strategy for the facile preparation of an enantioselective conglomerate with planar chirality. Therefore, to explore the feasibility of this concept, we report a molecular design strategy for an N-heteroacene focusing on inducing chirality using a donor. We synthesized an asymmetric donor–acceptor (D-A)-type derivative, FcTANC, composed of ferrocene (Fc) and tetraazanaphthacene (TANC). Solution-state ¹H NMR measurements revealed the free rotation of the single bond between Fc and TANC on the NMR time scale. Single-crystallographic X-ray analysis revealed that FcTANC generated three types of crystal polymorphs, specifically, one racemic and two enantiometric conglomerates. Also, the UV–visible absorption spectra of FcTANC have a peak derived from the metal-to-ligand charge transfer showing solvatochromic behavior. Cyclic voltammetry showed three reversible peaks derived from electron-donating Fc and electron-accepting TANC.