title: Influence of halogen substituents on the self-assembly of oligothiophenes--a combined STM and theoretical approach.
abstract: Iodinated quaterthiophenes 2-3 have been synthesized and their self-assembling behavior investigated at the liquid-solid interface by means of high-resolution scanning tunneling microscopy in comparison to parent oligothiophene 1. All three compounds spontaneously give well-ordered 2D crystalline monolayers at the graphite surface and order in a lamella-type arrangement of the conjugated backbones concomitant with an interlocking of the alkyl side chains. Symmetrically substituted oligothiophenes 1 and 3 without a relevant dipole moment self-assemble in a similar fashion, exhibiting comparable unit cells, whereas monoiodo derivative 2 arranges as pairs along the lamella axis due to the presence of a permanent dipole moment induced by the polarizable halogen group. Corroborated by quantum chemical calculations, novel head-to-head (iodo-iodo) intermolecular interactions were found to take place for this unsymmetrical derivative. The investigation of mixed solutions clearly reveals that at the solid-liquid interface a homogeneous layer of this compound is formed, which comprises the highest packing density leading to a separation process at the interface.
authors.affiliation: Abteilung Organische Chemie II, Universitat Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: Mohamed M S
authors.initials: MM
authors.lastname: Abdel-Mottaleb
authors.forename: Günther
authors.initials: G
authors.lastname: Götz
authors.forename: Pinar
authors.initials: P
authors.lastname: Kilickiran
authors.forename: Peter
authors.initials: P
authors.lastname: Bäuerle
authors.forename: Elena
authors.initials: E
authors.lastname: Mena-Osteritz