https://phys.org/news/2018-12-self-sorting-molecular-geometries.html

Asakawa and members of the AFM group conducted experiments with molecules called pillar[n]arenes, with n = 5 and n = 6, corresponding to pentagonal and hexagonal shapes, respectively. Both molecules come in two 'flavors': positively (cationic) or negatively charged (anionic). The polygonal molecules are essentially rings of 5 or 6 identical organic units, each featuring a benzene ring, but the composition of the units is different for the cationic and the anionic variants.

Ogoshi and his colleagues of the Supramolecular group let cationic pillar[5]arenes (P[5]+ in shorthand notation) adsorb on a quartz substrate. From this structure, they were able to grow P[5]+/P[5]–/P[5]+/… multilayers by immersing it alternatingly in anionic and cationic pillar[5]arene solutions. The addition of a layer was verified each time by ultraviolet-visible spectroscopy measurements. The resulting overall structure is a 'nanomat' of tubular structures with pentagonal pores. Similar results were obtained for the pillar[6]arenes: stacks of alternating cationic and anionic layers of the hexagonal molecules could be easily fabricated. The arrangement of pillar[n]arenes on a surface was investigated by collaboration with Prof. Takanori Fukushima, Prof. Tomofumi Tada and co-workers from Tokyo Institute of Technology.