Probing Matrix Effects in the Course of Electron Transfer across a Self-Assembled Monolayer

Abstract

Charge transport across a self-assembled monolayer (SAM) can involve either individual molecules only (throughbond model) or also intermolecular pathways (through-film model or matrix effects). In this context, we test a possible involvement of the latter pathways in the electron transfer (ET) across a model, nitrile-terminated naphthalene-2-thiolate (NC-Nap) SAM on Au(111). For this purpose, we apply the so-called core-holeclock approach in the framework of resonant Auger electron spectroscopy, allowing the measurement of the characteristic ET time from the nitrile tail group of NC-Nap to the substrate. The efficiency of possible intermolecular pathways depends on the electronic coupling between individual NC-Nap molecules, which was progressively reduced by mixing NC-Nap with short-chain alkanethiolates in binary SAMs. It turns out that the value of the characteristic ET time, estimated as 24 ± 4 fs for the reference, single-component NC-Nap SAM, does not vary noticeably in the binary monolayers, independent of the NC-Nap content. This means that the matrix effects play a negligible role for ET dynamics in the given model SAM, strongly favoring the through-bond CT model.

Probing the Effect of the Density of Active Molecules in Large-Area Molecular Junctions

“…In other words, the observed variation of J o , does not demonstrate a significant modifications of the cooperative effects between oligo­(BTB) wires with the decrease of the density of active wires despite the modifications of the interchain interactions. These results agree with theoretical predictions showing a linear scaling of conduction properties with the number of conducting molecules in junctions ( g ( N ) = N geff­(1)) and agree that, in the off-resonant tunneling regime, the effective single molecule conduction (geff(1)) can be higher than the corresponding single molecule property ( g (1)). , They also agree with recent experimental results …”

“…55,71 They also agree with recent experimental results. 72 Next, β-CD molecules were removed to create holes inside the BTB@β-CD layer, to give a BTB@hole layer. BTB oligomers were then grafted into the holes by a second diazonium electroreduction to create BTB@BTB layers.…”