Dynamics of Electron Transfer in Self-Assembled Monolayers with Acene Backbone

Taking the specifically designed self-assembled monolayers (SAMs) of nitrile-substituted anthracenethiolates (NC-AntS) and -selenolates (NC-AntSe) on Au(111) as target systems and combining the results with literature data for the analogous films with the naphthalene backbone, we studied electron transfer (ET) dynamics across the molecular acene “wire”. As the experimental tool, we used resonant Auger electron spectroscopy, processing the data within the core hole clock framework. These experiments were accompanied by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy measurements. Both NC-AntS and NC-AntSe films were found to be well-defined and have similar packing density, orientational order, and molecular inclination. The characteristic ET time for NC-AntS/Au and NC-AntSe/Au was estimated at 42 ± 8 and 40 ± 8 fs, respectively. The ET dynamics attenuation factor for the acene backbone (βET) and time associated with ET across the S–Au anchor were estimated at ∼0.25 Å–1 and ∼1.5 fs, respectively. The same value (∼1.5 fs) was obtained for the Se–Au anchor, indicating a similar efficiency of both docking groups in terms of ET dynamics and, presumably, in terms of the static electric properties as well. Comparison of the derived βET value for the anthracene and naphthalene SAMs with the analogous static values found for the anthracene dithiols gives a good agreement, verifying the static attenuation factor corresponding to a good coupling to the electrodes.