Department of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
Langmuir. 2012 Jan 10;28(1):71-83. doi: 10.1021/la202611w. Epub 2011 Sep 29.
The spontaneous assembly of aromatic cation radicals (D(+•)) with their neutral counterpart (D) affords dimer cation radicals (D(2)(+•)). The intermolecular dimeric cation radicals are readily characterized by the appearance of an intervalence charge-resonance transition in the NIR region of their electronic spectra and by ESR spectroscopy. The X-ray crystal structure analysis and DFT calculations of a representative dimer cation radical (i.e., the octamethylbiphenylene dimer cation radical) have established that a hole (or single positive charge) is completely delocalized over both aromatic moieties. The energetics and the geometrical considerations for the formation of dimer cation radicals is deliberated with the aid of a series of cyclophane-like bichromophoric donors with drastically varied interplanar angles between the cofacially arranged aryl moieties. X-ray crystallography of a number of mixed-valence cation radicals derived from monochromophoric benzenoid donors established that they generally assemble in 1D stacks in the solid state. However, the use of polychromophoric intervalence cation radicals, where a single charge is effectively delocalized among all of the chromophores, can lead to higher-order assemblies with potential applications in long-range charge transport. As a proof of concept, we show that a single charge in the cation radical of a triptycene derivative is evenly distributed on all three benzenoid rings and this triptycene cation radical forms a 2D electronically coupled assembly, as established by X-ray crystallography.
芳香正离子自由基（D(+•)）与它们的中性对应物（D）自发组装形成二聚阳离子自由基（D(2)(+•)）。通过电子光谱中近红外区域的价间电荷共振跃迁和 ESR 光谱，可以很容易地对分子间二聚阳离子自由基进行特征化。代表性二聚阳离子自由基（即八甲基联苯二聚阳离子自由基）的 X 射线晶体结构分析和 DFT 计算已经确定，一个空穴（或单个正电荷）完全定域在两个芳族部分上。借助一系列具有极大的芳基部分之间的平面间角的类环烷二色体给体，详细讨论了形成二聚阳离子自由基的能量学和几何考虑因素。从单色苯并类给体衍生的许多混合价阳离子自由基的 X 射线晶体学表明，它们通常在固态中以 1D 堆叠组装。然而，使用具有单电荷有效定域在所有发色团上的多色体间隔阳离子自由基，可以导致具有在长程电荷输运中潜在应用的高阶组装。作为概念验证，我们表明，三并苯衍生物的阳离子自由基中的单个电荷均匀分布在所有三个苯环上，并且该三并苯阳离子自由基形成二维电子耦合组装，这是通过 X 射线晶体学确定的。
