Redox active ordered arrays via metal initiated self-assembly of terpyridine based ligands

The interfacial reaction of terpyridyl-pendant poly-amido amine (PAMAM) dendrimers (dend-n-tpy; n = 4, 8, 32) and of bis-terpyridine containing bridging ligands (tpy-bridge-tpy), dissolved in CH2Cl2, with aqueous Fe2+ or Co2+ gives rise to film formation on HOPG and Pt(111) single crystal surfaces. Molecularly resolved STM images reveal that these films form highly ordered 2-D trigonal arrays, which appear to be composed of one-dimensional polymeric strands with a repeat unit of (tpy-dendrimer-tpy-M)(x), in the case of dendrimers, or (tpy-bridge-tpy-M)(x), in the case of the bridging ligands. An extensive study with ligands of tailored architecture has been carried out, providing insight on the relationship between the ligand's molecular structure and that of the resulting films. The formation of ordered domains appears to be controlled, at least in part, by the rigidity of the molecule containing the terpyridine groups. Films derived from bridging ligands containing long chains did not give rise to observable periodic structures, whereas, rotationally hindered bridging ligands gave rise to well-ordered films. The use of optically active ligands gave rise to helical structures whose sense was dependent on the chirality of the molecule employed. The physical extension of the ordered domains appears to be delimited by terrace width on the HOPG surface. The dimensions obtained from an analysis of STM images are consistent with the estimated size (from molecular modeling) of the molecules from which the films were derived. In all cases, the films are electrochemically active and exhibit a metal based reversible wave at a formal potential that corresponds to that for the respective [M(tpy)(2)](+2) complex.