Communication: Ion mobility of the radical cation dimers: (Naphthalene)2+• and naphthalene+•-benzene: Evidence for stacked sandwich and T-shape structures

Abstract

Dimer radical cations of aromatic and polycyclic aromatic molecules are good model systems for a fundamental understanding of photoconductivity and ferromagnetism in organic materials which depend on the degree of charge delocalization. The structures of the dimer radical cations are difficult to determine theoretically since the potential energy surface is often very flat with multiple shallow minima representing two major classes of isomers adopting the stacked parallel or the T-shape structure. We present experimental results, based on mass-selected ion mobility measurements, on the gas phase structures of the naphthalene+. . naphthalene homodimer and the naphthalene+. . benzene heterodimer radical cations at different temperatures. Ion mobility studies reveal a persistence of the stacked parallel structure of the naphthalene+. . naphthalene homodimer in the temperature range 230-300 K. On the other hand, the results reveal that the naphthalene+. . benzene heterodimer is able to exhibit both the stacked parallel and T-shape structural isomers depending on the experimental conditions. Exploitation of the unique structural motifs among charged homo- and heteroaromatic-aromatic interactions may lead to new opportunities for molecular design and recognition involving charged aromatic systems.