Covalent Immobilization of Redox-Active Fe(κ²‑dppe)(η⁵‑C₅Me₅)‑Based π‑Conjugated Wires on Oxide-Free Hydrogen-Terminated Silicon Surfaces

Several redox-active Fe­(κ2-dppe)­(η5-C5Me5) arylacetylide complexes (dppe = 1,2-bis­(diphenylphosphino)­ethane) featuring a pendant ethynyl (1b–d and 2) or ethenyl (3) group have been grafted on oxide-free hydrogen-terminated silicon (Si–H) surfaces through a covalent interfacial Si–C bond. They form densely packed redox-active monolayers. The charge-transfer process between the terminal redox center and the underlying silicon interface was subsequently studied by cyclic voltammetry. The latter turned out to be strongly dependent on the nature of the spacer linking the organometallic end groups to the silicon surface, the highest charge-transfer rates being obtained for monolayers anchored through conjugated and unsaturated spacers. Although the rates measured were among the highest values obtained for redox-active systems grafted to Si–H surfaces, this study nevertheless suggests that the electron tunnelling is not entirely controlling the interfacial charge-transfer process for the shorter linkers tested. In this respect, strategies to improve further the charge-transfer kinetics of the produced redox-active films are briefly discussed.多款带有悬挂乙炔基（1b–d与2）或乙烯基（3）的氧化还原活性Fe(κ²-dppe)(η⁵-C₅Me₅)芳基乙炔化物配合物（其中dppe为1,2-双(二苯基膦)乙烷，1,2-bis(diphenylphosphino)ethane），通过界面共价Si-C键接枝至无氧化层氢封端硅（Si-H）表面，形成密堆积的氧化还原活性单分子层。随后通过循环伏安法（cyclic voltammetry）研究了末端氧化还原中心与底层硅界面间的电荷转移过程。研究发现，该电荷转移过程强烈依赖于连接有机金属端基与硅表面的间隔基性质：采用共轭不饱和间隔基锚定的单分子层具有最高的电荷转移速率。尽管所测得的速率属于接枝至Si-H表面的氧化还原活性体系中的最高值之一，但本研究仍表明，对于本次测试的较短连接臂，电子隧穿并未完全主导该界面电荷转移过程。基于此，本文简要讨论了进一步提升所得氧化还原活性薄膜电荷转移动力学的相关策略。