Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
J Am Chem Soc. 2010 May 19;132(19):6817-21. doi: 10.1021/ja1015348.
We have measured the conductance and characterized molecule-electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine-gold bond allows two distinct conductance states that are accessed as the gold-molecule-gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the pi* orbital.
我们通过在分子溶液中拉长和压缩金点接触,测量了四个吡啶末端分子的电导并描述了分子-电极结合的几何形状。我们发现所有吡啶末端分子都表现出双稳态电导特征,这表明吡啶-金键的性质允许两个不同的电导状态,当金-分子-金结被拉长时可以进入这两个状态。我们已经确定低电导状态对应于分子在金电极之间完全伸展的状态,其中接触之间的距离与分子的长度相关;高电导状态是由于分子以一定角度结合。对于所有分子,我们发现低电导状态下结伸长的分布是相同的,而在高电导状态下,最可能的伸长长度与分子长度呈线性关系增加。对于低电导几何形状的四个分子的第一性原理电导计算结果与实验结果吻合良好,表明在共轭吡啶连接的分子中主要的导电通道是通过 pi*轨道。