The spectral and electrochemical properties of phenylazonapthalene based on self-assembled monolayer

A thiol-terminated phenylazonaphthalene derivative, namely 1-mercapto-6[1-(4-phenylazonaphthoxy)]hexane 1, was synthesized by diazo coupling of aniline with 1-napthol, etherification with 1,6-dibromohexane and thitol derivatization, subsequently. By self-assembly technology, the compound was spontaneously absorbed on thin, optically transparent gold film and formed stable self-assembled monolayer (SAM). The self-assembly course was monitored by UV-visible absorption spectra which gave direct evidence for the self-assembly mechanism of self-assembled monolayer, i.e., chemically adsorbed firstly, then came through a long-time orientation. Meanwhile, cyclic voltammogram was employed to study the electrochemical reduction and oxidation of the immobilized phenylazonaphthalene. The single molecular area obtained using the two methods was almost the sam : ca. 0.9nm². The irreversibility of the electrode process, sluggish reaction and reduction peak splitting all were originated from the well molecular orientation, not the dense packing in the SAM. This implied the process of oxidation and reduction accompanied the molecular conformation change which needed more free space for the movement of the molecular chain during the electrode processes.