Department of Chemistry, Boston University, 24 Cummington St., Boston, Massachusetts 02215, United States.
J Am Chem Soc. 2012 Dec 5;134(48):19709-15. doi: 10.1021/ja307373r. Epub 2012 Nov 20.
Two novel arene-bridged cycloparaphenylene dimers (1 and 2) were prepared using a functionalized precursor, bromo-substituted macrocycle 7. The preferred conformations of these dimeric structures were evaluated computationally in the solid state, as well as in the gas and solution phases. In the solid state, the trans configuration of 1 is preferred by 34 kcal/mol due to the denser crystal packing structure that is achieved. In contrast, in the gas phase and in solution, the cis conformation is favored by 7 kcal/mol (dimer 1) and 10 kcal/mol (dimer 2), with a cis to trans activation barrier of 20 kcal/mol. The stabilization seen in the cis conformations is attributed to the increased van der Waals interactions between the two cycloparaphenylene rings. These calculations indicate that the cis conformation is accessible in solution, which is promising for future efforts toward the synthesis of short carbon nanotubes (CNTs) via cycloparaphenylene monomers. In addition, the optoelectronic properties of these dimeric cycloparaphenylenes were characterized both experimentally and computationally for the first time.
两个新型的芳桥联环并苯二聚体（1 和 2）是使用功能化的前驱体，即溴取代的大环 7 制备的。这些二聚体结构的优选构象通过计算在固态、气相和溶液相中进行了评估。在固态中，由于实现了更密集的晶体堆积结构，1 的反式构型优先，高出 34 kcal/mol。相比之下，在气相和溶液中，顺式构象优先，高出 7 kcal/mol（二聚体 1）和 10 kcal/mol（二聚体 2），顺式到反式的活化能垒为 20 kcal/mol。在顺式构象中观察到的稳定性归因于两个环并苯环之间增加的范德华相互作用。这些计算表明，顺式构象在溶液中是可及的，这为通过环并苯单体合成短碳纳米管（CNT）的未来努力提供了希望。此外，这些二聚环并苯的光电性质也是首次通过实验和计算进行了表征。
