Dipartimento di Chimica, Università degli Studi di Roma La Sapienza, piazzale Aldo Moro 5, I-00185 Rome, Italy.
J Chem Phys. 2012 Apr 7;136(13):134308. doi: 10.1063/1.3698283.
We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the σ/π hyperconjugation in EtFC and the π-conjugation in VFC and EFC.
我们展示了通过同步辐射 C 1s 光吸收（NEXAFS）和光电子能谱（C 1s XPS）光谱以及密度泛函理论（DFT）计算，对单取代乙基、乙烯基和乙炔基二茂铁（EtFC、VFC 和 EFC）自由分子的实验和理论研究结果。这种组合研究旨在阐明取代基的 C-C 键不饱和程度对二茂铁衍生物电子结构的作用。当二茂铁用于分子电子混合器件时，需要这些取代基来实现分子化学锚定到相关表面上。高分辨率 C 1s NEXAFS 光谱具有独特的特征，这些特征取决于烃取代基的不饱和程度。考虑到 NEXAFS 光谱由三个部分组成的理论方法，使得可以将取代基基团对实验光谱的特定贡献与其不饱和程度分开。根据 DFT 计算的不同取代基和环戊二烯基（Cp）环碳原子的 IE 值，从实验数据分析得出 C 1s IE。在二茂铁系列中，观察到取代基碳原子和 Cp 环取代原子的化学位移具有明显的趋势。计算出的 IE 模式根据影响 IE 值的初始和最终状态效应进行了合理化，特别考虑了 Cp 环和取代基之间电子共轭的不同机制，即 EtFC 中的 σ/π超共轭和 VFC 和 EFC 中的 π 共轭。
