Charge and adsorption height dependence of the self-metalation of porphyrins on ultrathin MgO(001) films,Physical Chemistry Chemical Physics

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Charge and adsorption height dependence of the self-metalation of porphyrins on ultrathin MgO(001) films
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2022-11-17 , DOI: 10.1039/d2cp04688a
Francesco Presel ₁ , Christian S Kern ₁ , Thomas G Boné ₁ , Florian Schwarz ₁ , Peter Puschnig ₁ , Michael G Ramsey ₁ , Martin Sterrer ₁

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We have experimentally determined the adsorption structure, charge state, and metalation state of porphin, the fundamental building block of porphyrins, on ultrathin Ag(001)-supported MgO(001) films by scanning tunneling microscopy and photoemission spectroscopy, supported by calculations based on density functional theory. By tuning the substrate work function to values below and above the critical work function for charging, we succeeded in the preparation of 2H-P monolayers which contain negatively charged and uncharged molecules. It is shown that the porphin molecules self-metalate at room temperature, forming the corresponding Mg–porphin, irrespective of their charge state. This is in contrast to self-metalation of tetraphenyl porphyrin (TPP), which occurs on planar MgO(001) only if the molecules are negatively charged. The different reactivity is explained by the reduced molecule-substrate distance of the planar porphin molecule compared to the bulkier TPP. The results of this study shed light on the mechanism of porphyrin self-metalation on oxides and highlight the role of the adsorption geometry on the chemical reactivity.

中文翻译：

超薄 MgO(001) 薄膜上卟啉自金属化的电荷和吸附高度依赖性

我们通过扫描隧道显微镜和光电子能谱实验确定了卟啉（卟啉的基本组成部分）在超薄 Ag(001) 支撑的 MgO(001) 薄膜上的吸附结构、电荷态和金属化态，并得到基于以下计算的支持密度泛函理论。通过将基底功函数调整到低于和高于充电临界功函数的值，我们成功制备了包含带负电和不带电分子的 2H-P 单分子层。结果表明，卟啉分子在室温下会自金属化，形成相应的镁卟啉，无论其电荷状态如何。这与四苯基卟啉 (TPP) 的自金属化相反，四苯基卟啉 (TPP) 仅当分子带负电时才会发生在平面 MgO(001) 上。与体积较大的 TPP 相比，平面卟啉分子的分子-底物距离缩短可以解释不同的反应性。这项研究的结果揭示了氧化物上卟啉自金属化的机制，并强调了吸附几何形状对化学反应性的作用。

更新日期：2022-11-22

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