Instituto de Ciencia Molecular (ICMol), Universidad de Valencia , Catedrático José Beltrán 2, 46980 Paterna, Spain.
J Am Chem Soc. 2014 Jun 11;136(23):8314-22. doi: 10.1021/ja5012417. Epub 2014 Jun 2.
The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift toward lower energies of the ligand energy levels and a reduction of the HOMO-LUMO gap. However, electron-transport measurements carried out at room temperature revealed a variable metal coordination effect depending on the anchoring group: upon metal coordination, the molecular conductance of thiol and ethynyl derivatives decreased, whereas that of pyridine derivatives increased. These differences reside on the molecular levels implied in the conduction. According to quantum-mechanical calculations based on density functional theory methods, the ligand frontier orbital lying closer to the Fermi energy of the leads differs depending on the anchoring group. Thereby, the effect of metal coordination on molecular conductance observed for each anchoring could be explained in terms of the different energy alignments of the molecular orbitals within the gold Fermi level.
本工作旨在深入了解金属配位对分子导线室温电导率的影响。为此，我们设计了一系列刚性、高导电性的配体，这些配体具有不同的末端基团（乙酰硫醇、吡啶和乙炔基），其中金属配位引起的构象变化可以忽略不计。在室温下的断键装置中测量了该系列分子导线及其相应的 Cu(I) 配合物的单分子电导特性。实验和理论数据表明，无论锚固基团如何，在所有情况下，金属配位都会导致配体能级的能量向更低的能量转移，并减小 HOMO-LUMO 能隙。然而，在室温下进行的电子输运测量显示，金属配位的效果因锚固基团而异：在金属配位后，硫醇和乙炔基衍生物的分子电导率降低，而吡啶衍生物的电导率增加。这些差异存在于传导所涉及的分子水平上。根据基于密度泛函理论方法的量子力学计算，与引线费米能级更接近的配体前沿轨道因锚固基团而异。因此，可以根据分子轨道在金费米能级内的不同能量排列来解释每种锚固的金属配位对分子电导的影响。
