Dispersion-Clamped Crystalline Supramolecular Columnar π-Stacks of Adamantyl-Substituted Pyrenes.

Despite their importance in supramolecular chemistry, zero-offset columnar π-stacks of polycyclic aromatic hydrocarbons (PAHs) are rarely observed in crystals because close cofacial packing is penalized by Pauli repulsion. Here we show a crystalline phase (CP) of adamantyl-substituted pyrene that exhibits one-dimensional, translationally aligned columnar π-stacks enabled by dispersion-assisted adamantyl "clamps". Single-crystal x-ray diffraction reveals an exceptionally short interplanar separation of 3.297(3) Å at 100 K. Energy-decomposition analysis shows that the adamantyl substituents provide larger dispersion stabilization relative to their Pauli penalty, rationalizing the formation of the zero-offset π-columns. The solution-to-crystal color shift is exceptionally large (ΔEobs = -0.761 eV), which exceeds exciton coupling contributions and is dominated by intermolecular orbital interactions captured by a frontier crystal orbital (FCO) model. To the best of our knowledge, both the translationally zero-offset π-columns and the large crystallization-induced red shift are unprecedented for ambient-pressure CPs of neutral, closed-shell hydrocarbon PAHs.