Chiral dendrimers on a Pt(100) surface investigated by scanning tunnelling microscopy

Abstract

Dendrimers are highly symmetrical macromolecules of nanometre scale consisting of branching units attached to a central polyfunctional core. The chiral core or the branching units influence the conformation of the dendrimer. Because dendrimers cannot easily be crystallized for diffraction studies, scanning probe methods are used to investigate the conformation of chiral dendrimers on a metal surface. Dendrimers of different size and symmetry were dissolved in CH2Cl2 , film cast onto a Pt(100) surface and investigated by scanning tunnelling microscopy (STM). Measurements performed under ambient conditions reveal a quasi-periodic structure that is dependent on the shape of the investigated dendrimers: there is a distinct difference between dendrimers of the same generation with two or three branches. Furthermore, dendrimers with two branches differing only in chirality seem to pack themselves onto the metal substrate differently. Reference measurements of benzene on the Pt(100) surface suggest that the electronic structure probed by the STM tip is probably due to the phenyl rings inside the dendrimer structure. This assumption is supported by low-temperature (77 K) STM measurements, providing higher resolution. Copyright © 1999 John Wiley & Sons, Ltd.