Discerning the Redox-Dependent Electronic and Interfacial Structures in Electroactive Self-Assembled Monolayers

作     者：Wong, Raymond A. Yokota, Yasuyuki Wakisaka, Mitsuru Inukai, Junji Kim, Yousoo 

作者机构：RIKEN Surface & Interface Sci Lab 2-1 Hirosawa Wako Saitama 3510198 Japan Toyama Prefectural Univ Grad Sch Engn 5180 Kurokawa Imizu Toyama 9390398 Japan Univ Yamanashi Clean Energy Res Ctr 4 Takeda Kofu Yamanashi 4008510 Japan 

出 版 物：《JOURNAL OF THE AMERICAN CHEMICAL SOCIETY》 (美国化学会志)

年 卷 期：2018年第140卷第42期

页      面：13672-13679页

核心收录：

学科分类：07[理学] 0703[理学-化学] 

基　　金：Japan Science and Technology Agency (JST) RIKEN FY2018 Incentive Research Projects 

主　　题：Work function Vocational Rehabilitation Oxidation Fc Structure-function relationships molecular orientation self-assembled monolayers Ultraviolet Photoelectron Spectroscopy Ion pairs 

摘      要：We explore the redox-dependent electronic and structural changes of ferrocene-terminated self-assembled monolayers (Fc SAMs) immersed in aqueous solution. By exploiting X-ray and ultraviolet photoelectron spectroscopy combined with an electrochemical cell (EC-XPS/UPS), we can electrochemically control the Fc SAMs and spectroscopically probe the induced changes with the ferrocene/ferrocenium (Fc/Fc(+)) redox center (Fe oxidation state), formation of 1:1 Fc(+)-ClO4- ion pairs, molecular orientation, and monolayer thickness. We further find the insignificant involvement of interfacial water in the Fc SAMs irrespective of redox state. Electrolyte dependencies could be identified with 0.1 M NaClO4 and HClO4 when probing partially oxidized Fc/Fc(+) SAMs. Corroborating the occurrence of electrochemically induced oxidation, EC-UPS shows that oxidation to Fc(+) is accompanied by a shift of the highest occupied molecular orbital toward higher binding energy. The oxidation to Fc(+) is also met with an increase in work function ascribed to the induced negative interfacial dipole caused by the presence of Fc(+)-ClO4- ion pairs along with a contribution from the reorientation of the Fc(+) SAMs. The reversibility of our observations is confirmed upon conversion from Fc(+) back to the neutral Fc. The approach shown here is beneficial for a broad range of redox-responsive systems to aid in the elucidation of structure-function relationships.