title: X-ray structural investigation of nonsymmetrically and symmetrically alkylated [1]benzothieno[3,2-b]benzothiophene derivatives in bulk and thin films.
abstract: A detailed structural study of the bulk and thin film phases observed for two potential high-performance organic semiconductors has been carried out. The molecules are based on [1]benzothieno[3,2-b]benzothiophene (BTBT) as conjugated core and octyl side groups, which are anchored either symmetrically at both sides of the BTBT core (C8-BTBT-C8) or nonsymmetrically at one side only (C8-BTBT). Thin films of different thickness (8-85 nm) have been prepared by spin-coating for both systems and analyzed by combining specular and grazing incidence X-ray diffraction. In the case of C8-BTBT-C8, the known crystal structure obtained from single-crystal investigations is observed within all thin films, down to a film thickness of 9 nm. In the case of C8-BTBT, the crystal structure of the bulk phase has been determined from X-ray powder diffraction data with a consistent matching of experimental and calculated X-ray diffraction patterns (Rwp = 5.8%). The packing arrangement of C8-BTBT is similar to that of C8-BTBT-C8, that is, consisting of a lamellar structure with molecules arranged in a "herringbone" fashion, yet with lamellae composed of two head-to-head (or tail-to-tail as the structure is periodic) superimposed molecules instead of only one molecule for C8-BTBT-C8. As for C8-BTBT-C8, we demonstrate that the same phase is observed in bulk and thin films for C8-BTBT whatever the film thickness investigated.
authors.affiliation: Département de Physique, Faculté des Sciences, and ‡Laboratoire de Chimie des Polymères, Faculté des Sciences, Université libre de Bruxelles (ULB) , Boulevard du Triomphe, 1050 Brussels, Belgium.
authors.forename: Gabin
authors.initials: G
authors.lastname: Gbabode
authors.forename: Michael
authors.initials: M
authors.lastname: Dohr
authors.forename: Claude
authors.initials: C
authors.lastname: Niebel
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Balandier
authors.forename: Christian
authors.initials: C
authors.lastname: Ruzié
authors.forename: Philippe
authors.initials: P
authors.lastname: Négrier
authors.forename: Denise
authors.initials: D
authors.lastname: Mondieig
authors.forename: Yves H
authors.initials: YH
authors.lastname: Geerts
authors.forename: Roland
authors.initials: R
authors.lastname: Resel
authors.forename: Michele
authors.initials: M
authors.lastname: Sferrazza