Direct Observation of the Symmetrical and Asymmetrical Protonation States in Molecular Crystals.

The symmetrical and asymmetrical protonation states are realized via the formation of intermolecular hydrogen bonds inside 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA) molecular crystals. With the protonation of H2 SO4 , BP4VA molecules are protonated symmetrically, while the molecules are asymmetrically protonated by introducing HCl. The different protonation states of BP4VA crystals result in various supramolecular interactions, aggregation states, and even tunable optical properties. It provides a fundamental principle to understand the effect of protonation in organic conjugated molecules and an approach to expanding the scope of organic functional materials.