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p-Carborane Conjugation in Radical Anions of Cage–Cage and Cage–Phenyl Compounds
The Journal of Physical Chemistry A ( IF 2.9 ) Pub Date : 2018-01-09 00:00:00 , DOI: 10.1021/acs.jpca.7b10885
Andrew R. Cook 1 , Michal Valášek 2 , Alison M. Funston 1, 3 , Pavel Poliakov 1 , Josef Michl 2, 4 , John R. Miller 1
Affiliation  

Optical electron transfer (intervalence) transitions in radical anions of p-carborane oligomers attest to delocalization of electrons between two p-carboranes cages or a p-carborane and a phenyl ring. Oligomers of the 12 vertex p-carborane (C2B10H12) cage, [12], with up to 3 cages were synthesized, as well as p-carboranes with one or two trimethylsilylphenyl groups, [6], attached to the carbon termini. Pulse radiolysis in tetrahydrofuran produced radical anions, determined redox potentials by equilibria and measured their absorption spectra. Density functional theory computations provided critical insight into the optical electron transfer bands and electron delocalization. One case, [6–12–6], showed both Robin–Day class II and III transitions. The class III transition resulted from a fully delocalized excess electron across both benzene rings and the central p-carborane, with an electronic coupling Hab = 0.46 eV between the cage and either benzene. This unprecedented finding shows that p-carborane bridges are not simply electron withdrawing insulators. In other cases with more than ∼1/2 of the excess electron localized on a [12], large cage distortions were triggered, producing a partially open cage with a nido-like structure. This resulted in class II transitions with similar Hab but massive reorganization energies. The computations also predicted delocalization in radical cations, but complexities in cation formation allowed only tentative experimental support of the predictions. The results with anions provide clear evidence for carborane conjugation that might be exploited in molecular wire materials, which are classically composed of all π-conjugated molecules.

中文翻译:

笼-笼和笼-苯基化合物的自由基阴离子中的对-碳硼烷共轭

对-碳硼烷低聚物的自由基阴离子中的光学电子转移(间隔)跃迁证明了两个p-碳硼烷笼子或p-碳硼烷和苯环之间电子的离域化。合成了具有最多3个笼子的12个顶点碳硼烷(C 2 B 10 H 12)笼子的低聚物[12]以及p具有一个或两个三甲基甲硅烷基苯基的碳氢化合物[6],连接至碳末端。四氢呋喃中的脉冲辐射分解产生自由基阴离子,通过平衡确定氧化还原电势并测量其吸收光谱。密度泛函理论计算为光学电子转移带和电子离域提供了重要的见识。一种情况[6–12–6]显示了Robin-Day II级和III级过渡。III类跃迁是由于在整个苯环和中心对-碳硼烷上都完全发生了离域化的过量电子,并且笼子与任一苯之间的电子耦合H ab = 0.46 eV。这一前所未有的发现表明,p-碳硼烷桥不仅仅是吸电子的绝缘体。在其他情况下具有多于〜1 / 2的局部上的[12]的过量的电子的,大笼子失真被触发,产生一个部分打开笼与状结构。这导致具有相似的H ab但具有大量重组能量的II类转变。该计算还预测了自由基阳离子中的离域,但是阳离子形成的复杂性仅对这些预测提供了实验性的支持。带有阴离子的结果为碳硼烷共轭提供了明确的证据,碳硼烷共轭可在分子线材中开发,分子线材通常由所有π共轭分子组成。
更新日期:2018-01-09
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