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.