From Breathing Pores to Three-Dimensional Ionic Self-Assembly Under Electrochemical Control

Molecular self-assembly at the solid–liquid interface is highly developed, yet still faces several challenges, in particular related to reaching into the third dimension. Here, we demonstrate the spontaneous and reversible transition between two- and three-dimensional self-assembly of a charged polyaromatic molecule at the solid–liquid interface under electrochemical conditions, using in situ scanning tunnelling microscopy. By tuning the interfacial potential, we can selectively organise our target molecules in an open porous pattern, stretch these pores to accommodate another molecule and form an auto-host–guest structure, or stack the building blocks in a stratified bilayer. Using a simple electrostatic model, we rationalise 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 findings could form the basis of electrochemically controlled dynamic host–guest systems and 3D structures such as artificial receptors.

References
[1] K. Cui, K.S. Mali, O. Ivasenko, D. Wu, X. Feng, M. Walter, K. Müllen, S. De Feyter, S.F.L. Mertens, Angew. Chem., Int. Ed. 53, 12951 (2014).
[2] K. Cui, O. Ivasenko, K. S. Mali, D. Wu, X. Feng, K. Müllen, S. De Feyter, S. F. L. Mertens, Chem. Commun. 50, 10376 (2014).