A Dipleiadiene-Embedded Aromatic Saddle Consisting of 86 Carbon Atoms

This study presents a new type of negatively curved nanographene (C₈₆ H₃₂ ) that contains an unprecedented pattern of heptagons. A tert-butylated derivative of C₈₆ H₃₂ was successfully synthesized using tetrabenzodipleiadiene as a key building block. This synthesis involved a ring expansion reaction as a key step to form the seven-membered rings in the framework of tetrabenzodipleiadiene. The single-crystal structure reveals a saddle-shaped molecule with a highly bent naphthalene moiety at the center of the polycyclic backbone. As found from the DFT calculations, this aromatic saddle is flexible at room temperature and has a saddle-shaped geometry as the dominant conformation. The DFT calculations along with experimental results show that the attachment of t-butyl groups to the central tetrabenzodipleiadiene moiety of nanographene C₈₆ H₃₂ can stabilize the saddle conformation and make this nanographene less flexible.