Squeezing, Then Stacking: From Breathing Pores to Three‐Dimensional Ionic Self‐Assembly under Electrochemical Control

Abstract

We demonstrate the spontaneous and reversible transition between the two- and three-dimensional self-assembly of a supramolecular system at the solid-liquid interface under electrochemical conditions, using in situ scanning tunneling microscopy. By tuning the interfacial potential, we can selectively organize our target molecules in an open porous pattern, fill these pores to form an auto-host-guest structure, or stack the building blocks in a stratified bilayer. Using a simple electrostatic model, we rationalize which charge density is required to enable bilayer formation, and conversely, which molecular size/charge ratio is necessary in the design of new building blocks. Our results may lead to a new class of electrochemically controlled dynamic host-guest systems, artificial receptors, and smart materials.

Bias-induced conformational switching of supramolecular networks of trimesic acid at the solid-liquid interface

“…Due to their relatively weak interaction strength with the supporting surface as compared with chemisorbed systems, the molecular and interfacial interactions governing the assembly provide enough flexibility to ensure good control over the structure formation and switching between different states becomes possible. So far, switching has been achieved through external stimuli such as light, [5][6][7][8][9][10][11] heat, [11][12][13][14][15][16][17] pH, 18 surface potential, 19,20 and ion triggers, 21,22 as well as by an electric field induced between a scanning tunneling microscope (STM) tip and a surface. 14,15,[23][24][25][26][27] Due to their reversibility and high directionality, physisorbed, hydrogen-bonded systems at the solid-liquid interfaces are promising candidates for producing smart surfaces.…”

Local Conformational Switching of Supramolecular Networks at the Solid/Liquid Interface

“…Accordingly, the systems studied so far included either metalÀorganic complexes with high intrinsic dipolar moments that can flip aligning to an external field 33À35 or ionized species being adsorbed/desorbed or restructured from the solution in response to a charged interface. 39,40 Specially challenging is the possibility to find robust and reproducible systems that can keep the same response and reversibility after numerous switching cycles.…”

Self-Limiting Adsorption of WO3 Oligomers on Oxide Substrates in Solution

“…Since the ratio between the number of coordinated water molecules on the fully hydrated surface and the bridging oxygen atoms is 1:1, internal acid–base equilibration of the surface is possible by combining eqs 2 and 3 : Because the overall charge at the surface remains zero during this equilibration, this situation corresponds to the point of zero charge (PZC), at which the surface can be considered in its “zwitterionic state”, by analogy with the acid–base behavior of amino acids close to their isoelectric point. The PZC of oxides as a pH-driven property should not be confused with the potential of zero charge of free-electron metals, which is the unique electric potential value where the immersed electrode carries neither positive nor negative excess charge; the latter is of pivotal significance in explaining electrochemical phenomena, ranging from anion adsorption 50 to self-assembly 51 and nanoparticle charging. 52 The acid–base equilibria of oxide surfaces are decisive for much of their chemical properties, 53 including stability of colloids, and as such also of vast practical importance.…”