Direct Visualization of Molecule Deprotonation on an Insulating Surface
Direct Visualization of Molecule Deprotonation on an Insulating Surface
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DOI：
10.1021/nn3025942
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发表时间：
2012-08-01
期刊：
影响因子：
17.1
通讯作者：
Kuehnle, Angelika
中科院分区：
文献类型：
--
作者：
Kittelmann, Markus;Rahe, Philipp;Kuehnle, Angelika
阐明表面上基本反应步骤的分子尺度细节对于在许多领域（包括催化和表面合成）中对分子反应性的基本理解是决定性的。在这里，沉积在方解石（101;4）上的2,5-二羟基苯甲酸（DHBA）在室温下通过非接触原子力显微镜原位进行去质子化。沉积后，分子形成两相共存，即瞬态条纹相和稳定致密相。对高分辨率非接触式原子力显微镜图像的详细分析表明，瞬态条纹相是块状相，这需要在羧酸部分之间形成氢键。随着时间的推移，条纹相转变为致密相，这可以用分子的去质子化来解释。在去质子化状态下，分子不能再形成氢键，而是用带负电的羧酸基锚定在表面的钙离子上。开尔文探针力显微镜图像直接证实了去质子化步骤，揭示了分子电荷的变化。
Elucidating molecular-scale details of basic reaction steps on surfaces is decisive for a fundamental understanding of molecular reactivity within many fields, including catalysis and on-surface synthesis. Here, the deprotonation of 2,5-dihydroxybenzoic acid (DHBA) deposited onto calcite (101;4) held at room temperature is followed in situ by noncontact atomic force microscopy. After deposition, the molecules form two coexisting phases, a transient striped phase and a stable dense phase. A detailed analysis of high-resolution noncontact atomic force microscopy images indicates the transient striped phase being a bulk-like phase, which requires hydrogen bonds between the carboxylic acid moieties to be formed. With time, the striped phase transforms into the dense phase, which is explained by the deprotonation of the molecules. In the deprotonated state, the molecules can no longer form hydrogen bonds, but anchor to the surface calcium cations with their negatively charged carboxylate group. The deprotonation step is directly confirmed by Kelvin probe force microscopy images that unravel the change in the molecular charge.