Electrochemistry of the Self-Assembled Monolayers of Dyads Consisting of Tripod-Shaped Trithiol and Bithiophene on Gold
作者:Toshikazu Kitagawa、Hiroaki Matsubara、Takao Okazaki、Koichi Komatsu
DOI:10.3390/molecules190915298
日期:——
Self-assembled monolayers (SAMs) of tripod-shaped trithiols, consisting of an adamantane core with three CH2SH legs and a bithiophene group, were prepared on a Au(111) surface. Adsorption in a tripod-like fashion was supported by polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) of the SAMs, which indicated the absence of free SH groups. Cyclic voltammetry showed an irreversible cathodic wave due to reductive desorption. The SAM also showed an anodic wave due to the single-electron oxidation of the bithiophene moiety without concomitant desorption of the molecules. Although oxidation was irreversible in the absence of a protecting group, it became reversible with the introduction of a terminal phenyl group. The charge of the oxidation was one-third that of the reductive desorption, confirming a three-point adsorption. The surface coverage was ca. 50% of that expected for the anti bithiophene conformation, which suggested that an increase in the surface area per molecule had been caused by the presence of an energetically high-lying syn conformer. In accordance with this, the line shape of the oxidation wave suggested an electrostatic repulsive interaction between neighboring molecules.
这项研究描述了在Au(111)表面上制备的三脚架状三硫醇自组装单分子层(SAMs)。主要研究结果如下:
1. 这种三脚架分子由金刚烷核心、三个CH2SH腿和一个联噻吩基团组成。
2. 通过偏振调制-红外反射吸收光谱(PM-IRRAS)证实了三脚架式吸附,因为没有检测到游离的SH基团。
3. 循环伏安法显示:
- 出现不可逆的阴极波,源于还原脱附
- 出现阳极波,源于联噻吩部分的单电子氧化,但分子不会脱附
- 没有保护基团时氧化是不可逆的,加入末端苯基后变为可逆
- 氧化电荷量是还原脱附电荷量的1/3,证实了三点吸附模式
4. 表面覆盖度约为反式联噻吩构象理论值的50%,这表明由于存在能量较高的顺式构象,每个分子占据的表面积增加。
5. 氧化波的线型表明相邻分子之间存在静电排斥作用。
这些发现对理解这类分子在金表面上的组装行为和电化学性质具有重要意义。