Ordered Arrays Generated via Metal-Initiated Self-Assembly of Terpyridine Containing Dendrimers and Bridging Ligands

Abstract

The interfacial reaction of the terpyridyl-pendant dendrimers (dend- n -tpy; n = 4, 8, 32) and of the bridging ligand 1,4-bis[4,4‘ ‘-bis(1,1-dimethylethyl)-2,2‘:6‘,2‘ ‘terpyridine-4‘-yl]benzene (BBDTB) dissolved in CH 2 Cl 2 with aqueous Fe 2+ or Co 2+ gives rise to film formation on highly oriented pyrolytic graphite surfaces. Molecularly resolved scanning tunneling microscopy (STM) images reveal that these films form highly ordered 2-D hexagonal arrays which appear to be composed of one-dimensional polymeric strands with a repeat unit of (tpy-dend-tpy-M) x in the case of dendrimers or (tpy-bridge-tpy-M) x in the case of BBDTB (M = Fe 2+, Co 2+ ). The extension of the ordered domains appears to be delimited by terrace width. The dimensions obtained from an analysis of STM images is consistent with the size of the dendrimer or the bridging ligand (obtained from molecular modeling) from which the films are derived. In the case of films derived from dend -n -tpy the ordering is dependent on the dendrimer generation. In all cases, the films are electrochemically active and exhibit a reversible wave at a formal potential that corresponds to the respective [M(tpy) 2 ] 2+ complex.