Electrochemical Behavior of the Naphtoquinone Anchored onto a Gold Electrode through the Self-Assembled Monolayers of Aminoalkanethiol

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Abstract
2,3-Dichloro-1,4-naphtoquinone (NQ) was anchored to a gold electrode surface through the self-assembled monolayers of aminoalkanethiols (AAT, HS(CH2)nNH2: n = 2, 5, and 8). The effect of the alkyl chain length of the AAT monolayer, which also acts as the spacer between the NQ molecule and the gold electrode surface, on the redox behavior of the immobilized NQ has been studied by using a voltammetric technique. The surface coverage of the anchored NQ was estimated to be 3.8 × 10−10 mol cm−2 in the case that 2-aminoethanethiol (HS(CH2)2NH2) was used as the monolayer constituent. The electron-transfer rate constant, ket, associated with the redox process of anchored NQ decreased from 9.7 s−1 at n = 2 to 0.78 s−1 at n = 8, with increasing the chain length of the AAT monolayer, though the redox potential of NQ was scarcely affected by the chain length. The tunneling barrier coefficient, β, of the electron transfer was estimated to be 0.36 Å−1, from the observed linear relationship between the ket value and the monolayer chain length.

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