Dynamics of Electron Transfer in Azulene-Based Self-Assembled Monolayers

Azulene is an attractive building block for molecular electronics design owing to the intrinsic charge separation within its sp²-carbon scaffold. In this context, the structure and molecular organization in self-assembled monolayers (SAMs) of unsubstituted and nitrile-functionalized azulenethiolates on Au(111) substrates were studied by a variety of complementary spectroscopic techniques. The molecule of 2-mercapto-6-cyanoazulene was specifically designed to be addressable within the core hole clock approach in the general framework of resonant Auger electron spectroscopy. The azulenic SAMs described herein were documented to be well-defined and densely packed, with their individual molecular constituents oriented upright with respect to the Au surface, but with considerable tilt and twist. The electron transfer (ET) properties of these azulenic SAMs were found to be comparable to those of analogous naphthalene-based monolayers, which suggests that the charge separation and the related dipole moment have a minor effect on dynamics of ET through the molecular framework. The characteristic time for the latter process, triggered by the [N 1s]π₁∗ excitation and occurring along the nitrile-backbone-substrate pathway, was estimated at 23 ± 4 fs.