The intermolecular interaction in aromatic cation clusters is rather different from that in the corresponding neutral complexes, because of the substantial additional electrostatic, inductive, and charge-transfer attraction arising from the positive charge distribution. Hence, neutral and cationic complexes often have rather different equilibrium structures and binding energies, corresponding to an ionization-induced switch in the preferred aromatic molecule-solvent recognition motif. These aromatic interactions are closely related to the chemical and biological recognition. This project aims at the IR spectroscopic and quantum chemical characterization of aromatic ion-ligand complexes isolated in the gas phase, through the formation of EU-Japan collaborative research network.