A Stable, Soluble, and Crystalline Supramolecular System with a Triplet Ground State

A supramolecular complex was constructed by encapsulation of a ³O₂ molecule inside an open-cage C₆₀ derivative. Its single-crystal X-ray diffraction analysis revealed the presence of the ³O₂ at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated ³O₂ after two-electron reduction. The ESR measurements displayed the triplet character as well as the anisotropy of the ³O₂. Additionally, the SQUID measurements also demonstrated the paramagnetic behavior above 3 K without an antiferromagnetic transition. Upon photoirradiation with visible light, three phosphorescent bands at the NIR region were observed, arising from the exited ¹O₂ generated by self-sensitization with the outer cage, whose lifetimes were not affected by the environments. These studies confirmed that the complex is a crystalline triplet system with incompatible “high spin density” but “small interspin interaction” properties.