Self-assembly and layer-by-layer deposition of metallosupramolecular perylene bisimide polymers

Abstract

2,2′:6′,2″-Terpyridine (tpy)-functionalized red and green perylene bisimide (PBI) building blocks were synthesized, and their metal-ion-directed self-assembly was studied in detail by ¹H NMR, DOSY NMR, and UV-vis spectroscopy. These studies revealed that the newly synthesized ditopic bis(tpy)-PBI ligands, in which the tpy units are directly connected to PBI moieties at the imide positions, form supramolecular coordination polymers upon addition of one equivalent of Zn(II) ions. Atomic force microscopy (AFM) investigations confirmed the formation of extended, rigid polymers with average chain lengths of up to 30–35 repeat units. These coordination polymers create closely packed films with linear arrangement on mica and HOPG surfaces. The Zn(II) centers were mapped by applying current imaging tunnelling spectroscopy (CITS) to the red-coloured polymer deposited on graphite surfaces. An enhanced local density of unoccupied states close to the Fermi energy was observed in positions with metal ions. Alternate multilayer films of two different coordination polymers were prepared by the layer-by-layer deposition technique and surface densities Γ of perylene bisimide chromophores in these films were determined.