Figure-Eight Arylene Ethynylene Macrocycle: Facile Synthesis and Specific Binding behavior Toward Hg2+

Figure-eight (lemniscular) shaped macrocycles, besides their esthetic beauty, often have interesting chiroptical properties. However, only limited figure-eight carbocyclic frameworks have been reported as yet and most of them have been acquired by dimerizing helicenes with inherently twisted structure. Herein a novel figure-eight carbocyclic framework, lemniscular arylene ethynylene macrocycles (AEM), was firstly synthesized form non-helical linked precursors. Through simply increasing the concentration of reaction solution, intramolecular cyclization was effectively suppressed, while intermolecular cyclization was significantly improved to obtain figure-eight macrocycle with acceptable yield. Scanning tunneling microscopy (STM) with submolecular resolution was firstly employed to confirm the figure-eight shape through molecular imaging. Furthermore, the figure-eight cyclization mechanism was systematically discussed. Interestingly, macrocycles bearing inner -NH2 groups (SPM-Q6-NH2, SPM-Q12-NH2) showed specific sensing behavior toward highly toxic Hg2+. Even more intriguing are that, compared to planar macrocycle SPM-Q6-NH2, its figure-eight dimmer (SPM-Q12-NH2) exhibited much stronger complexation with Hg2+. This first study of synthesizing figure-eight conjugated carbocyclic framework from an inherently non-helical precursor opens up new way to construct figure-eight macrocycles. More importantly, with this figure-eight AEM as molecular platform, further structurally derivations can be achieved through simple cycloaddition reaction with unsaturated bonds (ethynylene bonds and diyne bonds) or introducing donor-acceptor(D-A) structure.