title: Characterization of self-assembled monolayers of oligo(phenyleneethynylene) derivatives of varying shapes on gold: effect of laterally extended pi-systems.
abstract: Fully conjugated organic molecules, such as the oligo(phenyleneethynylene) (OPE) systems, are of growing interest within the field of molecular electronics, as is the self-assembly of well-defined molecular thin films with predefined functions. The structure and function of such films are intimately related and governed by the structures of their molecular constituents, through the intermolecular interactions and the interactions between the molecules and the substrate, onto which the film is assembled. Here we report on the synthesis of a series of three OPE derivatives, with the general structure phenylethynylene-aryl-ethynylenephenylene-headgroup, and the structural investigation of the self-assembled monolayers (SAMs) formed from them on Au(111) surfaces. The SAMs were characterized by infrared reflection-absorption spectroscopy, spectroscopic ellipsometry, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy. The effective thickness of the SAMs was observed to decrease as the pi-system of the aryl moiety of the OPE adsorbate was extended perpendicular to its molecular long axis. Changing the aryl moiety from benzene to naphthalene to anthracene resulted in lower molecular surface densities and larger molecular inclination. The average tilt angles for the benzene, naphthalene, and anthracene SAMs were found to be about 30 degrees , 40 degrees , and 42 degrees from the surface normal, respectively. For the largest adsorbate, the anthracene derivative, there is spectroscopic evidence suggesting the existence of nonequivalent binding sites. The differences observed between the SAMs are rationalized in terms of the shape of the adsorbates and the strength of the pi-pi interactions between them.
authors: Department of Chemical and Biological Engineering, Chalmers University of Technology, S-41296 Göteborg, Sweden.
authors: Daniel
authors: D
authors: Nilsson
authors: Somsakul
authors: S
authors: Watcharinyanon
authors: Mattias
authors: M
authors: Eng
authors: Liqian
authors: L
authors: Li
authors: Ellen
authors: E
authors: Moons
authors: Lars S O
authors: LS
authors: Johansson
authors: Michael
authors: M
authors: Zharnikov
authors: Andrey
authors: A
authors: Shaporenko
authors: Bo
authors: B
authors: Albinsson
authors: Jerker
authors: J
authors: Mårtensson