Characterization and application of [60]Fullerene-metal cluster self-assembled monolayers (SAMs)

Abstract

The metal cluster derivative of $C_{60}$, $Os_{3}(CO)_{8}(CN(CH_{2})_{3}Si(OEt)_{3})(μ_{3}-η^{2}:η^{2}:η^{2}-C_{60})$ (2) has been prepared from initial decarbonylation of $Os_{3}(CO)_{9}(μ_{3}-η^{2}:η^{2}:η^{2}-C_{60})$ (1) with $Me_{3}NO/MeCN$ and subsequent reaction with 3-(triethoxysilyl)propyl isocyanide. The cyclic voltammogram (CV) of 2 exhibits three quasi-reversible redox waves. The first and second waves are attributed to successive one-electron reductions, while the third corresponds to overlapped two one-electron processes, due to electronic communication between the $C_{60}$ and metal cluster center. The SAM of 1 (1/ITO) was prepared by reaction of 1 and 3-(triethoxysilyl)propyl amine-modified ITO, and the SAMs of 2 (2/ITO and 2/Au) were prepared by immersing an ITO electrode and $HO(CH_{2})_{6}SH$ -treated Au electrode in a solution of 2, respectively. The CV of 1/ITO shows two broad redox waves with large cathodic shifts as previously reported for other $C_{60}$-based SAMs. In contrast, the CV results for SAMs of 2 reveal three, well-resolved redox waves, which are very similar to the electrochemical behavior of 2 in solution. The hydrophobicity of the resulting $C_{60}$-modified surface was confirmed by contact angle measurements. The determination of the surface morphology and chemical composition was carried out by using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Decarbonylation of compound 2 with $Me_{3}NO/MeCN$ followed by reaction with the isocyanide functionalized Zn porphyrin (ZnP-NC) afforded $Os_{3}(CO)_{7}(CNR)(CNR``)(μ_{3}-η^{2}:η^{2}:η^{2}-C_{60})$ $(5; R = (CH_{2})_{3}Si(OEt)_{3}, R`` = ZnP)$. The SAM of 5 (5/ITO) was prepared by immersion of an ITO electrode in a solution of 5 and DABCO (2 : 1 equiv). The SAM of 5 has been characterized by UV-Vis absorption spectroscopy, water contact angle, XPS, and cyclic voltammetry. The CV of 5/ITO reveals three, well-resolved redox waves. The third wave...