Fluorinated self-assembled monolayers (SAMs) have been utilized in a variety of applications such as transistors and optoelectronic devices. However, in most SAMs the fluorinated groups could not be positioned in high proximity to the surface due to steric effects. This limitation hinders the direct analysis of the impact of the fluorination level on surface properties. Herein, fluorinated aromatic N-heterocyclic carbenes (NHCs), with 1–5 fluorine atoms, were self-assembled on a gold substrate. These NHCs enabled the positioning of fluorinated groups in high proximity to the metal surface to identify the influence of the fluorination level on surface properties. Experimental measurements and theoretical calculations identified that all fluorinated NHCs formed SAMs and adopted a flat-lying adsorption configuration while anchored to the metal surface via Au adatom. A higher fluorination level induced a stronger interaction of the fluorinated side groups with the Au surface. The stronger interaction and surface proximity of the fluorinated side groups deteriorated the overall binding energy of the NHC due to the less-optimized adsorption geometry of the carbene carbon. Ultraviolet photoelectron spectroscopy measurements revealed that fluorinated NHC monolayers lowered the surface work function by up to 1 eV and induced an increase of 15–20° in the water contact angle. The impact on surface properties did not vary according to the fluorination level of NHCs, and similar values were measured for NHC with 1–5 fluorine atoms. It is therefore identified that dominant adsorbate–substrate interactions between the fluorinated side groups and the Au surface quenched the distinct impact of the fluorination level on surface functionality.

中文翻译：

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强底物-吸附物相互作用直接指导氟化 N-杂环卡宾单分子层对 Au 表面性能的影响


氟化自组装单层 （SAM） 已用于各种应用，例如晶体管和光电器件。然而，在大多数 SAM 中，由于空间效应，氟化基团无法定位在离表面高度接近的位置。这种限制阻碍了对氟化水平对表面特性影响的直接分析。在此，具有 1-5 个氟原子的氟化芳香族 N-杂环卡宾 （NHC） 在金衬底上自组装。这些 NHC 能够将氟化基团定位在非常靠近金属表面的位置，以确定氟化水平对表面特性的影响。实验测量和理论计算确定，所有氟化 NHC 都形成 SAM，并在通过 Au 吸附原子锚定到金属表面时采用平躺吸附配置。较高的氟化水平诱导氟化侧基与 Au 表面的相互作用更强。由于卡宾碳的吸附几何形状不太优化，氟化侧基更强的相互作用和表面接近性降低了 NHC 的整体结合能。紫外光电子能谱测量表明，氟化 NHC 单层将表面功函数降低了 1 eV，并导致水接触角增加了 15-20°。对表面性能的影响不随 NHC 的氟化水平而变化，并且对具有 1-5 个氟原子的 NHC 测得的值相似。因此，可以确定氟化侧基和 Au 表面之间的主要吸附物-底物相互作用淬灭了氟化水平对表面功能的独特影响。