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.

Interactions of Nucleic Acid Bases with Temozolomide. Stacked, Perpendicular, and Coplanar Heterodimers

“…Auguring well for our own data above, these authors found good agreement between their experimental measurements and calculated data. Prior work has extended as well to radical cation dimers − where both experimental and calculated data have shown that both stacked and perpendicular arrangements can occur in homo and heterodimers of aromatics. These geometries can at times be quite competitive in terms of energy, as for example in the case of the naphthalene/benzene dimer.…”

Nucleophilic Aromatic Addition in Ionizing Environments: Observation and Analysis of New C–N Valence Bonds in Complexes between Naphthalene Radical Cation and Pyridine

“…For the mobility measurements, the neutral naphthalene and naphthalene–pyridine clusters are generated in the source chamber by supersonic pulsed adiabatic expansion. , During operation, a vapor mixture consisting of 230 Torr pyridine (C 5 H 5 N) (Aldrich, 99.9%) and 3.9 Torr naphthalene (C 10 H 8 ) (Aldrich, ≥99%) in 5100 Torr helium (ultrahigh purity, Airgas 99.99%) is expanded through a conical nozzle (500 μm in diameter) in pulses of 300–400 μs duration at a repetition rate of 100 Hz. The jet is skimmed and passed into the second chamber, which is maintained at 2 × 10 –6 Torr, where the clusters are ionized by 70 eV electrons.…”

“…The ions are injected into the drift cell containing 1.0 Torr helium at different temperatures (200–300 K) using injection energy of 12.8 eV (lab frame). Mobility measurements are made by injecting a narrow pulse of ions into the drift cell. , The ion gate located just prior to the cell entrance (see Figure S1, Supporting Information) chops the pulse to a narrow, 30–50 μs wide packet, which enters the drift cell. As the ions are injected into the drift cell, the injection energy is dissipated by collisions with the helium buffer gas.…”

Formation of the Charge‐Localized Dimer Radical Cation of 2‐Ethyl‐9,10‐dimethoxyanthracene in Solution Phase

“…[30,31] The charged istribution in the dimer radicalc ation conformers and the formation of covalent bond-linked dimers in gas phase have been discussed in other aromatic systems as well. [36][37][38] Despite such extensives tudies, the formationo fd imer radicalc ations and the nature of chargel ocalization/delocalization are not fully understood, especially for molecular units that are more complicated than simple benzene-type units.…”

“…Although a slipped face‐to‐face configuration has been accepted as the dominant species characterized by a charge resonance band in solution and gas phases, other tilted face‐to‐face dimers, and T‐shaped dimer radical cations with charge localization have also been discussed as possible conformations . The charge distribution in the dimer radical cation conformers and the formation of covalent bond‐linked dimers in gas phase have been discussed in other aromatic systems as well . Despite such extensive studies, the formation of dimer radical cations and the nature of charge localization/delocalization are not fully understood, especially for molecular units that are more complicated than simple benzene‐type units.…”