Intramolecular Interaction, Photoisomerization, and Mechanical C–C Bond Dissociation of 1,2-Di(9-anthryl)benzene and Its Photoisomer: A Fundamental Moiety of Anthracene-Based π‑Cluster Molecules

We report variable and unique properties of 1,2-di­(9-anthryl)­benzene 1 as a fundamental moiety of anthracene-based π-cluster molecules. Due to a through-space π-conjugation between anthracene units, excimer emission at room temperature and charge delocalized state in radical cation state of 1 could be observed. Photoirradiation to 1 afforded an intramolecular [4 + 4] cyclized anthracene dimer 1′ having a high strain energy with long C–C bond that exceeded 1.68 Å, resulting in C–C bond dissociation by simple mechanical grinding.