Kinetic Dispersion in Redox-Active Dithiocarbamate Monolayers

Dithiocarbamates (dtcs) have been implicated as important gold-binding groups in Molecular electronics. Dies have two alkane branches connected at a single anchoring point that hits a bidentate resonance structure. Forming readily in situ by the combination or secondary amines and CS2, dtcs adsorb quickly onto gold surfaces. Electroactive self-assembled monolayers (eSAMs) were prepared by the coadsorption of ferrocene dialkyldithiocarbamates (Fc dtcs) with diluent dies on gold electrodes. Short and long alkane chains were used (11 and 16 methylene groups, respectively), and a polar ester group was incorporated. Cyclic voltammetry (CV) shows that the electrochemistry is quasi-reversible. At high surface coverage, the peak separations and full widths at half-maximum for Fc dtcs deviate from theoretical values and are analogous to that of ferrocene alkane thiols oil gold at high surface coverage. Importantly, these features do not change at low Fc die surface coverage as observed for Ferrocene alkane thiols. Ferrocene dtcs were used to label monolayer defect sites and to demonstrate the exchange of surface-bound dtcs with solution dies. Finally, the rate of electron transfer was analyzed using Tafel plots and ac voltammetric methods. The results for both techniques are consistent with a kinetically disperse population of redox sites. The length of the diluent alkane chain appears to have an effect oil the distribution of electron-transfer rates, likely because of the eSAM structure. This work indicates that Structurally, Fc dtc eSAMs are fundamentally different from alkane thiol SAMs on gold.