Synergistic Enhancement of Hydrogen-Bonding and Charge-Transfer Interactions in a Crystal of an Anthranol–Acridine Dyad Comprised of a Hydrogen-Bonded Chain Aggregate

A dyad comprised of a derivative of anthranol with an improved electron-donating ability and a derivative of acridine having an improved electron-accepting ability was prepared using a palladium-catalyzed C–H arylation process. The dyad assembles to form two crystal polymorphs, one with a color close to that of the dyad in solution and the other with a completely different color. The polymorphs are comprised of hydrogen-bonded chain aggregates that have different hydrogen-bonding motifs. Structural and spectroscopic analyses showed that the unusually colored crystals possess a stronger intermolecular hydrogen bond. In addition, this crystal displays a charge-transfer (CT) absorption band, corresponding to one-electron transfer from the anthranol unit to the acridine unit, that is red-shifted and enhanced relative to those of the other crystal and the dyad in solution. The combined theoretical and experimental results suggest that hydrogen-bonding and charge-transfer interactions take place synergistically in the unusually colored crystals.