Chiral Monolayers with Achiral Tetrapod Molecules on Highly Oriented Pyrolytic Graphite
Hitoshi Asakawa, Sayaka Matsui, Quang Thang Trịnh, Hajime Hirao, Yasuhide Inokuma, Tomoki Ogoshi, Saki Tanaka, Kayo Komatsu, Akio Ohta, Tsuyoshi Asakawa, Takeshi Fukuma
Abstract
The self-assembly of organic molecules at the surface of highly oriented pyrolytic graphite (HOPG) is a promising process for constructing molecular-scale architectures. However, selectable organic molecules are generally restricted to two-dimensional molecules with planar π-conjugated structures and alkyl chains. We herein present the formation of self-assembled monolayers of tetrakis(4-ethynylphenyl)methane (TEPM) having a three-dimensional (3D) tetrapod geometry on HOPG, which was achieved by utilizing a simple spin-coating method. The arrangements of TEPM molecules in the monolayers were investigated using frequency-modulation atomic force microscopy (FM-AFM). The resulting subnanometer-resolution FM-AFM images revealed that the TEPM molecules formed linear rows with a periodicity of 0.85 nm oriented in a parallel configuration but with two alternating intervals of 0.7 and 1.0 nm. Moreover, the TEPM monolayers were classified into two chiral types with a relationship of mutual mirror-image symmetry, according to the observed molecular arrangements. Our results demonstrate the capability of TEPM molecules to act as 3D building blocks for the design of molecular-scale architectures at interfaces.