Breaking π–π Interactions in Carboxylic Acid Monolayers on Rutile TiO 2 (110) Leads to Unexpected Long-Range Ordering
Breaking π–π Interactions in Carboxylic Acid Monolayers on Rutile TiO 2 (110) Leads to Unexpected Long-Range Ordering
复制标题
打破金红石 TiO 2 (110) 上羧酸单层中的 β-β 相互作用导致意外的长程有序化
DOI：
10.1021/acs.jpcc.8b11501
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Hines, Melissa A.
中科院分区：
文献类型：
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作者：
DeBenedetti, William J.;Hines, Melissa A.
羧酸是超分子和表面化学中普遍存在的结构单元，因为它们与金属阳离子具有很强但可逆的结合力。在这些应用中，酸的相对顺序和方向会影响性能。我们提出了一种调整分子间相互作用的合理方法，其目标是保持有利的分子构象，同时实现长程有序。特别是，我们表明，在水溶液中产生的金红石（110）上的多氟苯甲酸酯单层的扫描隧道显微镜（STM）图像显示出非常大（2×1）的颗粒，而没有在类似制备的苯甲酸酯单层中观察到的分子间配对。配对的缺乏归因于电负性的氟取代基，它减少了相邻分子上的苯基之间的π-π或四极相互作用，并稳定了芳香族头基和羧酸盐结合部分之间的有利构型。尽管头部基团之间的相互作用减少，但大晶粒尺寸表明分子间相互作用能显着超过热能。考虑到相邻分子之间的间隔为 6.6 Å，这些强烈的相互作用令人惊讶。从分子分辨 STM 图像中定量测量分子间相互作用能比色散校正密度泛函理论预测的结果大 7 倍。讨论了这种差异的一些可能的根源。这一发现为生产高度有序的单分子层和大分子超结构提供了一条新途径。
Carboxylic acids are ubiquitous building blocks in supramolecular and surface chemistry because of their strong but reversible binding to metal cations. In these applications, the relative ordering and orientation of the acids can affect performance. We present a rational approach to tuning intermolecular interactions with the goal of maintaining a favorable molecular conformation while also enabling long-range ordering. In particular, we show that scanning tunneling microscopy (STM) images ofm- orp-fluorobenzoate monolayers on rutile (110) produced in aqueous solutions display very large (2 × 1) grains without the intermolecular pairing observed in similarly prepared benzoate monolayers. The lack of pairing is attributed to the electronegative fluorine substituent, which reduces π–π or quadrupolar interactions between the phenyl groups on the adjacent molecules and stabilizes a favorable configuration between the aromatic head group and the carboxylate-binding moiety. In spite of the reduced interactions between the head groups, the large grain sizes are indicative of intermolecular interaction energies that significantly exceed thermal energy. These strong interactions are surprising given the 6.6 Å separation between the adjacent molecules. Quantitative measurements of the intermolecular interaction energies from molecularly resolved STM images are a factor of ∼7 larger than those predicted by dispersion-corrected density functional theory. A number of possible origins for this discrepancy are discussed. This finding suggests a new path to the production of highly ordered monolayers and superstructures of large molecules.