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In the crystal structure of the title compound, C8H18N22+·2I−·CH3CN, the dication lies on a mirror plane containing the mol­ecular dication threefold axis. The structure displays C—H⋯I inter­actions between H atoms of the 1,4-dimethyl-1,4-diazo­nia­bicyclo­[2.2.2]octane dication and the iodide anions. The H⋯I distances are in the range 2.96–3.18 (4) Å. The dications pack forming channels along the b axis, which contain the iodide anions and acetonitrile solvent mol­ecules. [ABSTRACT FROM AUTHOR]

A series of new quinodimethane-substituted terthiophene and quaterthiophene oligomers has been investigated for comparison with a previously studied quinoid oligothiophene that has demonstrated high mobilities and ambipolar transport behavior in thin-film transistor devices. Each new quinoidal thiophene derivative shows a reversible one-electron oxidation between 0.85 and 1.32 V, a quasi-reversible one-electron second oxidation between 1.37 and 1.96 V, and a reversible two-electron reduction between -0.05 and -0.23 V. The solution UV-vis-NIR spectrum of each compound is dominated by an intense (∊ ≅ 100000 M-1 cm-1) low energy π-π* transition that has a λmax ranging between 648 and 790 nm. All X-ray crystal structures exhibit very planar quinoidal backbones and short intermolecular π-stacking distances (3.335-3.492 Å). Structures exhibit a single 21-stacking distance with parallel cofacial stacking (sulfur atoms of equivalent rings pointed in the same direction) or with alternating distances and antiparallel cofacial stacking (sulfur atoms of equivalent rings pointed in the opposite direction). Examples of the layered and herringbone-packing motifs are observed for both the parallel and the antiparallel cofacial stacking. Analysis of the X-ray structures and molecular orbital calculations indicates that all of these compounds have one-dimensional electronic band structures as a result of the π-stacking. For structures with a unique π-stacking distance, a simple geometric overlap parameter calculated from the shape of the molecule and the slip from perfect registry in the π-stack correlates well with the transfer integrals (t) calculated using molecular orbital theory. The calculated valence (633 meV) and conduction (834 meV) bandwidths for a quinoid quaterthiophene structure are similar to those calculated for the benchmark pentacene and indicate that both hole and electron mobilities could be significant. [ABSTRACT FROM AUTHOR]