2D Structural Modulation by Odd-Even Effect of Alkyl Chains Revealed by Scanning Tunneling Microscopy at Solid/Liquid Interface

Abstract

This review paper presents our recent progress on the formation of self-assembled two-dimensional (2D) structures, and their modulation by the odd-even effect of alkyl chains on porphyrin derivatives, isobutenyl compounds and bipyridine derivatives. The 2D structures were directly visualized by scanning tunneling microscopy (STM) at the highly oriented pyrolytic graphite (HOPG)/solvent interface. The alkyl tails in the compounds work as moleculemolecule and molecule-substrate interaction sites, and the nature of the 2D structures depended on the alkyl chain length. These STM observations revealed that, for each compound, an odd-even effect exists for a specific range of alkyl chain lengths.

Functionalized 4,4′-Bipyridines: Synthesis and 2D Organization on Highly Oriented Pyrolytic Graphite

“…In agreement with literature data for 2,2′-bipyridines, the two C 18 alkyl chains on compound 2 seem sufficient to ensure the physisorption on HOPG, whereas four chains are needed when using shorter alkyl substituents (C 13 ). Intermolecular interactions favor a packing motif in which the shorter alkyl chains are not interdigitated but simply arranged in an antiparallel fashion to maximize van der Waals contacts, in good agreement with previous reports on 2,2′-bipyridines bearing four octyl chains .…”