Chiral Monolayers with Achiral Tetrapod Molecules\non Highly Oriented Pyrolytic Graphite

Abstract

The\nself-assembly of organic molecules at the surface of highly\noriented pyrolytic graphite (HOPG) is a promising process for constructing\nmolecular-scale architectures. However, selectable organic molecules\nare generally restricted to two-dimensional molecules with planar\nπ-conjugated structures and alkyl chains. We herein present\nthe formation of self-assembled monolayers of tetrakis­(4-ethynylphenyl)­methane\n(TEPM) having a three-dimensional (3D) tetrapod geometry on HOPG,\nwhich was achieved by utilizing a simple spin-coating method. The\narrangements of TEPM molecules in the monolayers were investigated\nusing frequency-modulation atomic force microscopy (FM-AFM). The resulting\nsubnanometer-resolution FM-AFM images revealed that the TEPM molecules\nformed linear rows with a periodicity of 0.85 nm oriented in a parallel\nconfiguration but with two alternating intervals of 0.7 and 1.0 nm.\nMoreover, the TEPM monolayers were classified into two chiral types\nwith a relationship of mutual mirror-image symmetry, according to\nthe observed molecular arrangements. Our results demonstrate the capability\nof TEPM molecules to act as 3D building blocks for the design of molecular-scale\narchitectures at interfaces.