Photoexcitation of gold nanoclusters covalently functionalized with 9-mesityl-10-methylacridinium ion (Mes-Acr(+)) resulted in the formation of the electron-transfer state (Mes(center dot+)-Acr(center dot)), which forms a pi-dimer radical cation with the neighboring Mes-Acr(+) via an intramolecular pi-pi a interaction.