Transport and transport-related phenomena in gated junctions based on molecules with floppy vibrational degrees of freedom

分子电子学代表了当前非常感兴趣的领域，旨在更深入地理解纳米尺度上化学、物理和工程的相互作用，这应该允许制造具有所需功能的分子电路。与C. D. Frisbie（明尼苏达大学）在该项目的第一个资助期内取得了许多成果，为基于软盘分子的纳米结中的运输和运输相关现象提供了重要的见解。在这些结果的基础上，这一提案的更新有两个目标。首先，受第一期研究结果的刺激，我们计划进一步联合理论-实验研究机械拉伸下的分子结。这些研究的强烈动机初步（未发表）的结果揭示了一个非常令人费解的基于软盘分子的纳米结的纳米弹性行为。鉴于这种完全不寻常的行为，我们强烈期望我们的工作将成为一个新的，有价值的贡献，纳米弹性完全。第二，在一个联合的理论-实验的努力，我们的目标是在文献中首次调查的电荷传输通过纳米结的基础上使用离子液体/凝胶，而不是普通的电解质的电解质门控下的软分子。这种实验方法最近由弗里斯比的有机电子学小组开创。在这一部分计划的理论研究不同于绝大多数现有的研究nanotransfer，假设分子在冻结的几何形状。为了解释可重组振动模式的存在，我们将对给定几何结构下计算的输运性质进行系综平均。在这个项目中采用的方法将扩展最近申请人的方法的基础上的一个单步描述的纳米运输。这种方法最近在生物化学和电化学界得到了认可，它不同于基于两步机制的共识描述。要执行的系综平均值是不平凡的，因为计算中所需的权重函数需要平衡结的吉布斯自由能，并且因为与松弛模式相关的重组与普通溶剂的重组在性质上不同。在主导分子轨道可以更接近电极费米能级的情况下，预期由于松弛模式及其温度（T）依赖性而产生的更强的波动效应。这可以通过电化学门控来实现，这是控制能量对准的最有效的设置。尽管如此，使用普通电解质可达到的T范围非常有限。使用离子液体/凝胶，可以探索相当宽的T范围。在这个项目中获得的理论结果，与同伴实验研究中出现的数据进行比较，将提供新的见解在纳米级的电荷传输。

Molecular electronics represents a field of great current interest aiming at a deeper understanding of the interplay of chemistry, physics, and engineering at the nanoscale, which should allow to fabricate molecular circuits with desired functionality. Extensive work done in collaboration with the experimental group of Prof. C. D. Frisbie (University of Minnesota) in the first funding period of this project yielded many results providing important insight into transport and transport-related phenomena in nanojunctions based on floppy molecules. Building on those results, this proposal renewal has two objectives. First, stimulated by findings from the first period, we plan further joint theoretical-experimental studies on molecular junctions under mechanical stretching. These studies are strongly motivated by preliminary (unpublished) results revealing a highly puzzling nanoelastic behavior of nanojunctions based on floppy molecules. In view of this completely unusual behavior, we strongly expect that our work will become a new, valuable contribution to nanoelasticiy altogether. Second, in a joint theoretical-experimental effort we aim at investigating for the first time in the literature the charge transport through nanojunctions based on floppy molecules under electrolyte gating using ionic liquids/gels instead of ordinary electrolytes. This experimental approach was recently pioneered by Frisbie's group in organic electronics. The theoretical studies planned in this part differ from the vast majority of existing studies on nanotransport, which assume molecules at frozen geometry. To account for the presence of reorganizable vibrational modes, we will perform ensemble averaging of the transport properties computed at given geometry. The approach to be employed in this project will extend a recent applicant's approach based on a single-step description of nanotransport. That approach, which received recently recognition in the biochemistry and electrochemistry communities, is different from the consensus description based on a two-step mechanism. The ensemble average to be performed is nontrivial because the weight function needed in calculations requires the Gibbs free energy of a junction out of equilibrium and because reorganization related to floppy modes is qualitatively different from that of common solvents. Stronger fluctuation effects due to floppy modes and their temperature (T) dependence are expected in cases where the dominant molecular orbital can be brought closer to electrode Fermi levels. This can be achieved by electrochemical gating, which is the most efficient setup to control energetic alignments. Still, T-ranges accessible using ordinary electrolytes are very limited. Using ionic liquids/gels, a considerably broader T-range can be explored. The theoretical results obtained in this project, to be compared with data emerging from companion experimental studies, will provide new insight into charge transport at the nanoscale.