Lawson Brent, Vidal Efrain, Luna Sigifredo, Haley Michael M, Kamenetska Maria
Department of Physics, Boston University, Boston, Massachusetts 02215, United States.
Department of Chemistry & Biochemistry, University of Oregon, Eugene, Oregon 97403, United States.
ACS Nano. 2024 Oct 22;18(42):29059-29066. doi: 10.1021/acsnano.4c10183. Epub 2024 Oct 11.
We achieve, at room temperature, conductance enhancements over 2 orders of magnitude in single molecule circuits formed with polycyclic benzoquinoidal () diradicals upon increasing molecular length by ∼5 Å. We find that this extreme and atypical anti-ohmic conductance enhancement at longer molecular lengths is due to the diradical character of the molecules, which can be described as a topologically nontrivial electronic state, and results in constructive interference between the frontier molecular orbitals. The distinct feature of the compounds studied here as molecular wires is that they are characterized by moderate diradical character in the neutral state, allowing for robust and facile measurements of their transport properties. We adapt the 1D-SSH model, originally developed to examine electronic topological order in linear carbon chains, to the polycyclic systems studied here and find that it captures the anti-ohmic trends in this molecular series. Specifically, our model reveals that the mechanism of conductance enhancement with length in polycyclic systems is constructive quantum interference between the frontier orbitals with nontrivial topology, which is present in acene-like, but not in linear, molecular systems. Importantly, we use our model to predict and experimentally validate that anti-ohmic trends can be engineered through synthetic adjustments of the diradical character of the acene-like molecules. Overall, we achieve extreme anti-ohmic enhancement and mechanistic insight into electronic transport in a class of materials that we identify here as promising candidates for creating highly conductive and tunable nanoscale wires.
在室温下，当由多环苯醌型（）双自由基形成的单分子电路中分子长度增加约5 Å时，我们实现了超过2个数量级的电导增强。我们发现，在较长分子长度下这种极端且非典型的反欧姆电导增强是由于分子的双自由基特性，这种特性可被描述为一种拓扑非平凡的电子态，并导致前沿分子轨道之间的相长干涉。这里作为分子导线研究的化合物的独特特征是，它们在中性状态下具有适度的双自由基特性，这使得对其传输性质进行稳健且便捷的测量成为可能。我们将最初用于研究线性碳链中电子拓扑序的一维SSH模型应用于这里研究的多环体系，发现它捕捉到了该分子系列中的反欧姆趋势。具体而言，我们的模型表明，多环体系中电导随长度增强的机制是具有非平凡拓扑的前沿轨道之间的相长量子干涉，这种干涉存在于类并苯分子体系中，而不存在于线性分子体系中。重要的是，我们使用我们的模型预测并通过实验验证，反欧姆趋势可以通过对类并苯分子的双自由基特性进行合成调节来设计。总体而言，我们在一类材料中实现了极端的反欧姆增强，并对电子输运机制有了深入了解，我们在此将这类材料确定为创建高导电性和可调谐纳米级导线的有前途的候选材料。
