Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States.
J Am Chem Soc. 2021 Feb 24;143(7):2638-2643. doi: 10.1021/jacs.0c12244. Epub 2021 Feb 15.
We report a large kinetic isotope effect (KIE) for intramolecular charge transport in π-conjugated oligophenyleneimine (OPI) molecules connected to Au electrodes. C and N substitution on the imine bonds produces a conductance KIE of ∼2.7 per labeled atom in long OPI wires >4 nm in length, far larger than typical heavy-atom KIEs for chemical reactions. In contrast, isotopic labeling in shorter OPI wires <4 nm does not produce a conductance KIE, consistent with a direct tunneling mechanism. Temperature-dependent measurements reveal that conductance for a long N-substituted OPI wire is activated, and we propose that the exceptionally large conductance KIEs imply a thermally assisted, through-barrier polaron tunneling mechanism. In general, observation of large conductance KIEs opens up considerable opportunities for understanding microscopic conduction mechanisms in π-conjugated molecules.
我们报告了在连接到 Au 电极的π-共轭聚亚苯基亚胺（OPI）分子中分子内电荷输运的大动力学同位素效应（KIE）。在亚胺键上进行 C 和 N 取代会导致在长 OPI 线（>4nm）中每个标记原子的电导 KIE 约为 2.7，远大于化学反应的典型重原子 KIE。相比之下，在短 OPI 线（<4nm）中进行同位素标记不会产生电导 KIE，这与直接隧道机制一致。温度相关的测量表明，长 N 取代的 OPI 线的电导被激活，我们提出，异常大的电导 KIE 意味着热辅助的、贯穿势垒极化子隧道机制。一般来说，观察到大的电导 KIE 为理解π-共轭分子中的微观传导机制提供了很大的机会。
