Supercycloalkanes: dihydropyrazine-embedded macrocycles with flexible conformations resembling cycloalkanes

Cycloalkanoid molecules are of fundamental interest due to their unique geometric structures and physical properties. However, studies on the molecular dynamics of these molecules tend to be difficult owing to labile conformations. Herein, we report a series of "supercycloalkanes", namely dihydropyrazine-embedded macrocycles, that show puckered structures imitating those of cyclobutane, cyclopentane and cyclohexane, as confirmed by crystal structures. ¹H NMR spectrum analyses and theoretical calculations reveal that the macrocycle containing four dihydropyrazine corners undergoes a ring-flapping process in solution, and the one with five dihydropyrazine corners involves a pseudorotation process. Photophysical results indicate that these macrocycles show donor (D)-acceptor (A)-type structures, resulting in solvent-dependent emissions. Moreover, each dihydropyrazine corner could effectively interact with fullerene molecules owing to the V-shaped π-surface. This study provides a series of cycloalkanoids with a "superstructure" and discloses the molecular dynamics of cycloalkanoid macrocycles.