Cycloparaphenylene and their radicals anchored to a metal−organic framework

Cycloparaphenylene (CPP) shows modulated photophysical and electronic properties due to its strained structure and radially oriented π-electron system. Incorporation of CPP into metal-organic frameworks (MOFs) could transfer its extensive properties in solution to porous solids. Moreover, with the unique arrangement of the macrocycles and their interactions with the framework, emerging characteristics are anticipated. As an example of “robust dynamics”, we synthesized the first MOF structure (FDM-1001) with CPP precisely anchored to the ordered framework by employing a [8]CPP-containing linear dicarboxylate linker. Metric relationship between the dynamic macrocycles and the robust backbone creates ideal π-π interactions between them, which leads to an essentially directional arrangement of [8]CPP in the three-dimensional space. Furthermore, the MOF with [8]CPP could be successfully oxidized to generate an infinite array of radicals that show enhanced air stability compared to its molecular analogue.     

Stable Crystalline Nanohoop Radical and Its Self-Association Promoted by van der Waals Interactions

A stable nanohoop radical (OR3) combining the structures of cycloparaphenylene and an olympicenyl radical is synthesized and isolated in the crystalline state. X-ray crystallographic analysis reveals that OR3 forms a unique head-to-tail dimer that further aggregates into a one-dimensional chain in the solid state. Variable-temperature NMR and concentration-dependent absorption measurements indicate that the π-dimer is not formed in solution. An energy decomposition analysis indicates that van der Waals interactions are the driving force for the self-association process, in contrast with other olympicenyl derivatives that favor π-dimerization. The physical properties in solution phase have been studied, and the stable cationic species obtained by one-electron chemical oxidation. This study offers a new molecular design to modulate the self-association of organic radicals for overcoming the spin-Peierls transition, and to prepare novel nanohoop compounds with spin-related properties.