Winkler Michael, Houk K N
Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
J Am Chem Soc. 2007 Feb 14;129(6):1805-15. doi: 10.1021/ja067087u. Epub 2007 Jan 24.
The successive replacement of CH moieties by nitrogen atoms in oligoacenes (benzene to hexacene) has been studied computationally at the B3LYP/6-311+G(d,p)//6-31G(d) level of theory, and the effects of different heteroatomic substitution patterns on structures, electron affinities, excitation, ionization, and reorganization energies are discussed. The calculated tendencies are rationalized on the basis of molecular orbital arguments. To achieve electron affinities of 3 eV, a value required to allow for efficient electron injection from common metal electrodes, at least seven nitrogen atoms have to be incorporated into tetracenes or pentacenes. The latter require rather small reorganization energies for electron transfer (<0.20 eV) making these compounds promising candidates for n-channel semiconducting materials. Particularly interesting are heptaazapentacenes 5 and 6 in which the nitrogen atoms are arranged to form self-complementary systems with a maximum number of intermolecular CH-N contacts in planar oligomers. These interactions are expected to facilitate the formation of graphite-like sheet structures with cofacial arrangements of the pi systems and short interlayer distances due to attractive N-C(H) interlayer interactions. This should not only be ideal for charge transfer but also might contribute to improved air stability of these semiconductors. Self-complementarity is maintained in azaacenes containing two cyano groups in the terminal rings. These compounds require lower reorganization energies than the unsubstituted heterocycles (0.13-0.14 eV), show high electron affinities (3.3 eV), and are thus promising candidates for materials applications.
在理论水平B3LYP/6 - 311 + G(d,p)//6 - 31G(d)上，通过计算研究了低聚并苯（从苯到并六苯）中CH基团被氮原子的连续取代情况，并讨论了不同杂原子取代模式对结构、电子亲和能、激发、电离和重组能的影响。基于分子轨道理论对计算得出的趋势进行了合理化解释。为了实现3 eV的电子亲和能（这是从普通金属电极有效注入电子所需的值），至少需要将七个氮原子引入并四苯或并五苯中。后者对于电子转移所需的重组能相当小（<0.20 eV），这使得这些化合物成为n沟道半导体材料的有前景的候选物。特别有趣的是七氮杂并五苯5和6，其中氮原子排列形成自互补体系，在平面低聚物中具有最大数量的分子间CH - N接触。由于有吸引力的N - C(H)层间相互作用，这些相互作用预计将促进形成具有π体系共面排列和短层间距离的类石墨片状结构。这不仅对于电荷转移应该是理想的，而且可能有助于提高这些半导体的空气稳定性。在末端环中含有两个氰基的氮杂并苯中保持了自互补性。这些化合物比未取代的杂环需要更低的重组能（0.13 - 0.14 eV），显示出高电子亲和能（3.3 eV），因此是材料应用的有前景的候选物。
