Qiao Xiaohang, Vezzoli Andrea, Smith Shaun, Higgins Simon J, Davidson Ross J, Beeby Andrew, Nichols Richard J
Department of Chemistry, University of Liverpool, Crown St, Liverpool L69 7ZD, U.K.
Department of Chemistry, Durham University, South Rd, Durham DH1 3LE, U.K.
J Phys Chem C Nanomater Interfaces. 2023 Jun 27;127(26):12802-12810. doi: 10.1021/acs.jpcc.3c03129. eCollection 2023 Jul 6.
The environment surrounding a molecular junction affects its charge-transport properties and, therefore, must be chosen with care. In the case of measurements in liquid media, the solvent must provide good solvation, grant junction stability, and, in the case of electrolyte gating experiments, allow efficient electrical coupling to the gate electrodes through control of the electrical double layer. We evaluated in this study the deep eutectic solvent mixture (DES) ethaline, which is a mixture of choline chloride and ethylene glycol (1:2), for single-molecule junction fabrication with break-junction techniques. In ethaline, we were able to (i) measure challenging and poorly soluble molecular wires, exploiting the improved solvation capabilities offered by DESs, and (ii) efficiently apply an electrostatic gate able to modulate the conductance of the junction by approximately an order of magnitude within a ∼1 V potential window. The electrochemical gating results on a Au--Au junction follow exceptionally well the single-level modeling with strong gate coupling (where VDP is 1,2-di(pyridine-4-yl)ethene). Ethaline is also an ideal solvent for the measurement of very short molecular junctions, as it grants a greatly reduced snapback distance of the metallic electrodes upon point-contact rupture. Our work demonstrates that DESs are viable alternatives to often relatively expensive ionic liquids, offering good versatility for single-molecule electrical measurements.
分子结周围的环境会影响其电荷传输特性，因此必须谨慎选择。在液体介质中进行测量时，溶剂必须提供良好的溶剂化作用，确保结的稳定性，并且在电解质门控实验中，通过控制双电层实现与栅电极的有效电耦合。在本研究中，我们评估了深共熔溶剂混合物（DES）乙酰胺，它是氯化胆碱和乙二醇（1:2）的混合物，用于采用断结技术制备单分子结。在乙酰胺中，我们能够：（i）利用DES提供的增强溶剂化能力，测量具有挑战性且难溶的分子线；（ii）在约1 V的电位窗口内，有效施加能够将结的电导调节约一个数量级的静电门。在金-金结上的电化学门控结果与强门耦合的单能级模型（其中VDP是1,2-二（吡啶-4-基）乙烯）非常吻合。乙酰胺也是测量非常短的分子结时的理想溶剂，因为它能使金属电极在点接触破裂时的回跳距离大幅减小。我们的工作表明，DES是通常相对昂贵的离子液体的可行替代品，为单分子电学测量提供了良好的通用性。
