STM visualisation of counterions and the effect of charges on self-assembled monolayers of macrocycles

Abstract

SummaryDespite their importance in self-assembly processes, the influence of charged counterions on the geometry of self-assembled organic monolayers and their direct localisation within the monolayers has been given little attention. Recently, various examples of self-assembled monolayers composed of charged molecules on surfaces have been reported, but no effort has been made to prove the presence of counterions within the monolayer. Here we show that visualisation and exact localisation of counterions within self-assembled monolayers can be achieved with scanning tunnelling microscopy (STM). The presence of charges on the studied shape-persistent macrocycles is shown to have a profound effect on the self-assembly process at the liquid–solid interface. Furthermore, preferential adsorption was observed for the uncharged analogue of the macrocycle on a surface.

Anion-induced dimerization of 5-fold symmetric cyanostars in 3D crystalline solids and 2D self-assembled crystals

“…Similar to other studies, the counterion species is not observed, [6][7][8] expect in a few cases. 23,24 We believe the solvated cation contributes to a diffuse double layer. 25 Height profiles of these bright features give an average stack at 1.4 Å above the other receptors (ESI, † Fig.…”

Selective Anion-Induced Crystal Switching and Binding in Surface Monolayers Modulated by Electric Fields from Scanning Probes

“…Furthermore, when considering ion binding at interfaces, counterions , must always be present for charge balance. Only once have counterions been seen; in that case iodide (I – ) appeared during STM imaging of a random 2D cocrystalline array of cationic (pyridinium-based) and neutral adsorbates. It is also surprising that among these cation-binding studies none have been investigated using the traditional approach of titrating the ions into solution but instead have relied upon the addition of a single equivalent of ion.…”

Adsorption of the organic salt TAB(HCl)4 on Cu(111) studied using STM and XPS

“…At liquid-solid interfaces, ISA has been investigated mainly in the context of electrochemistry, [12][13][14][15] and adsorption structures formed from organic salts have been studied using scanning tunneling microscopy 16 including one example where counter ions were identified in a self-assembled molecular surface structure. 17 At vacuum-solid interfaces, experiments have recently been reported where metal atoms/ions, in particular alkali metals acting as metallic cations, have been co-deposited with organic species resulting in ordered structures attributed to electrostatic interactions. [18][19][20][21] Many organic compounds can be obtained as organic salts, leading to the question of whether such salts can be sublimated stoichiometrically in vacuo and whether the constituent species preserve at least part of their charge after adsorption, allowing their self-assembly to be affected or driven by electrostatic ionic interactions.…”