title: Oxadiazole-metal interface: from isolated molecules to pi-stacking.
abstract: Derivatives of 2,5-diaryl-1,3,4-oxadiazole are used widely for electron transport in organic light emitting diodes (OLED). This study addresses the structure of 2,5-diphenyl-1,3,4-oxadiazole (PPD) molecules on Cu(111) using scanning tunneling microscopy (STM) and density function theory (DFT): at incomplete coverage, PPD molecules are found horizontally on the surface; once the surface area is insufficient to accommodate all adsorbates in this fashion, a pi-stacked film of vertically arranged molecules is formed. In contrast to bulk PPD, in this film, the molecules are arranged face-to-face at a separation of square root(3a0) = 4.4 A as imposed by the substrate interatomic spacing along the [-2 1 1] direction.
authors.affiliation: Pierce Hall, University of California-Riverside, Riverside, California 92521, USA. ki-young.kwon@email.ucr.edu
authors.forename: Ki-Young
authors.initials: KY
authors.lastname: Kwon
authors.forename: Xing
authors.initials: X
authors.lastname: Lin
authors.forename: Greg
authors.initials: G
authors.lastname: Pawin
authors.forename: Kin
authors.initials: K
authors.lastname: Wong
authors.forename: Ludwig
authors.initials: L
authors.lastname: Bartels