Two-dimensional self-assembly of a porphyrin-polypyridyl ruthenium(II) hybrid on hopg surface through metal-ligand interactions.

The synthesis and self-assembly behavior of porphyrin-polypyridyl ruthenium(II) hybrid, which consists of a flexible alkyl chain attached with two conjugated moieties is described. The electronic absorption spectrum and emission spectra show that the [C(8)-TPP-(ip)Ru(phen)(2)](ClO(4))(2), abbreviated as (C(8)ip)TPPC has optical properties. Scanning tunneling microscopy (STM) studies found that the pi-pi interaction and metal-ligand interaction allow (C(8)ip)TPPC to form self-assembled structure and have an edge-on orientation on the highly oriented pyrolytic graphite (HOPG) surface. The multidentate structure in (C(8)ip)TPPC molecules act as linkers between the molecules and form metal-ligand coordination, which forces the assembly process in the direction of stable columnar arrays. In addition, although the sample was stored for two months in ambient conditions, STM experiments showed that the order of (C(8)ip)TPPC self-assembly only slightly decreased which indicates that the self-assembled monolayer is stable. This work demonstrates that introducing a metal-ligand in the porphyrin-polypyridyl compound is a useful strategy to obtain novel surface assemblies.