Non‐Buckling Stacks of Nanocarbon Molecules

An octagon‐centered nanocarbon molecule, phenine dehydrogenated tetramethano‐ o ‐tetraphene (phenine dH‐ToT), is reported. The synthesis employed machine‐learning‐augmented concentration‐dependent yield analysis (ML+CYAN) to optimize a tetrameric macrocyclization while simultaneously extracting kinetic information. Crystallographic analysis revealed a unique molecular structure featuring a flattened octagon center surrounded by alternating pentagon and hexagon rims with slight buckling. In the crystal, two molecules were azimuthally offset to form an S 8 ‐symmetric dimer stack with a pentagon‐over‐hexagon arrangement. Detailed variable‐temperature NMR studies revealed that the S 8 ‐dimer was assembled in an entropy‐driven manner and remains frozen without buckling dynamics in solution, in contrast to the rapid buckling dynamics observed for saddle‐shaped phenine [ n ]circulene dimers. Upon dissociation into monomers, phenine dH‐ToT was liberated to undergo buckling dynamics and was observed as a time‐averaged D 4h ‐symmetric species. These results demonstrate the key role of polygonal arrangements in controlling buckling dynamics in nanocarbon bilayer stacks.