Covalent molecular functionalization allows the physicochemical properties of 2D materials to be precisely tuned and modulated on-demand. Nonetheless, research on the molecular functionalization of 2D monoelemental graphene-like materials─known as Xenes─remains scarce, being mainly restricted to a specific type of solid-state chemical reaction based on the topotactic transformation of bulkier Zintl phases. Herein, a robust and general chemical approach is reported for the direct functionalization of commercially available H-terminated 2D germanene (2D-GeH) with thiolated molecules (R-SH) via Ge–S bond formation. While the material characterization data provide direct experimental evidence of the Ge–S chemical bonding, density functional theory (DFT) calculations also predict its existence. Remarkably, the anchored thiolated molecules also favor the passivation of the 2D Xene against air oxidation, enlarging its benefits for real implementation. As a proof-of-principle, a redox-responsive molecular moiety such as 6-(ferrocenyl)hexanethiol (Fc₆-SH) has been exploited to induce changes in the optoelectronic properties of the resulting 2D-GeFc₆ heterostructure by simply modulating the external bias potential, making it possible to optically and electrically read out a molecular switch on 2D Xene via implanting molecular responsiveness. Remarkably, the ON/OFF ratio has been shown to be dependent on the distance between the redox-responsive Fc moiety and the 2D Xene surface through the alkyl chain length. Overall, the reported a-la-carte molecular engineering approach provides the basis toward the rapid development of stable 2D-GeR derivatives exhibiting molecule-programmable properties.

中文翻译：

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H 封端 2D 锗烷与硫醇化分子的直接共价官能化：光电特性的钝化和调节


共价分子功能化允许按需精确调整和调制 2D 材料的物理化学性质。尽管如此，关于 2D 单元素石墨烯类材料（称为 Xenes）的分子功能化的研究仍然很少，主要局限于基于体积较大的 Zintl 相的拓扑定向转变的特定类型的固态化学反应。在此，报道了一种稳健的通用化学方法，用于通过 Ge-S 键形成将市售的 H 封端 2D 锗烯 （2D-GeH） 与硫醇化分子 （R-SH） 直接官能化。虽然材料表征数据提供了 Ge-S 化学键合的直接实验证据，但密度泛函理论 （DFT） 计算也预测了它的存在。值得注意的是，锚定的硫醇化分子还有利于 2D Xene 的钝化以防止空气氧化，从而扩大了其实际实施的好处。作为原理验证，已经利用了氧化还原响应性分子部分，例如 6-（二茂铁基）己硫醇 （Fc 6-SH），通过简单地调节外部偏置电位来诱导所得 2D-GeFc 6 异质结构的光电性质的变化，从而可以通过植入分子响应性在 2D Xene 上光学和电学地读出分子开关。值得注意的是，开/关比已被证明取决于氧化还原响应性 Fc 部分与 2D Xene 表面之间通过烷基链长度的距离。 总体而言，报道的 a-la-carte 分子工程方法为快速开发具有分子可编程特性的稳定 2D-GeR 衍生物提供了基础。