Controlled Activation of Substrate Templating in Molecular Self-Assembly by Deprotonation

Abstract

Templated assembly of organic molecules constitutes a promising approach for fabricating functional nanostructures at surfaces with molecular-scale control. Using the substrate template for steering the adsorbate growth enables creating a rich variety of molecular structures by tuning the subtle balance of intermolecular and molecule−surface interactions. On insulating surfaces, however, surface templating is largely absent due to the comparatively weak molecule−surface interactions compared to metallic substrates. Here, we demonstrate the activation of substrate templating in molecular self-assembly on a bulk insulator by controlled deprotonation of the adsorbed molecules upon annealing. Upon deposition of 4-iodobenzoic acid onto the natural cleavage plane of calcite held at room temperature, high molecular mobility is observed, indicating a small diffusion barrier. Molecular islands only nucleate at step edges. These islands show no commensurability with the underlying substrate, clearly indicating the absence of surface templating. Upon annealing the substrate, the molecules undergo a transition from the protonated to the deprotonated state. In the deprotonated state, the molecules adopt a well-defined adsorption position, resulting in a distinctly different, substrate-templated molecular structure that is stable at room temperature. Our work, thus, demonstrates the controlled activation of substrate templating by changing the molecule−surface interaction upon annealing.

Mechanisms of Covalent Dimerization on a Bulk Insulating Surface

“…These upright-standing molecules form islands that are shown in Figure 2b. 32 Upon annealing to 580 K, a second structural change is observed. This structural change has previously been assigned to dehalogenation and dimerization of two IBA molecules to form biphenyl-4,4′-dicarboxylic acid (BPDCA, referred to for simplicity as "dimer" in the remainder of this work).…”

“…29−31 These achievements have been reviewed in refs 6 and 8, focusing on the relevant experimental and theoretical studies to date, respectively. Despite the considerable progress achieved on metal surfaces, comparatively fewer studies of synthesis on insulating substrates are available in the literature, including reactions on bulk surfaces through Ullmann-type processes, 3,6,19,32 photochemical initiation, 20 and reactions on insulating thin films 18 (see also ref 6 and references therein). Several factors make on-surface syntheses on insulators rather challenging.…”

Self-assembly of Organic Molecules on Insulating Surfaces

“…An example that is ascribed to this anchoring mechanism is 4-iodobenzoic acid on the (104) cleavage plane of calcite [96], as shown in Fig. 9.8.…”

“…The interaction is expected to significantly increase in strength if not only polar molecules are present, but if molecular ions are employed [73,96]. An example that is ascribed to this anchoring mechanism is 4-iodobenzoic acid on the (104) cleavage plane of calcite [96], as shown in Fig.…”

Increasing the Templating Effect on a Bulk Insulator Surface: From a Kinetically Trapped to a Thermodynamically More Stable Structure

“…[20][21][22][23] One way of creating a stable wetting layer on the calcite (10.4) surface has been proposed via the deprotonation of a benzoic acid derivatives. 24,25 In the latter study, Non-Contact Atomic Force Microscopy (NC-AFM) experiments performed at room temperature 25 have revealed that the 2,5-dihydroxybenzoic acid (DHBA) molecules form two ordered phases: one consisting of alternating stripes with different apparent height (a striped phase) and the other, more uniform, made of a network of regular spots (a dense phase). The striped phase has been observed to completely disappear over time at room temperature, while, correspondingly, existing dense phase islands have increased in size and number.…”