Crystallization of Tyrian purple (6,6′-dibromoindigo) thin films: The impact of substrate surface modifications

Magdalena Truger, Andrew O F Jones, Anna Maria Coclite, Stefan Pachmajer, Dominik Kriegner, Christian Röthel, Josef Simbrunner, Ingo Salzmann, Roland Resel*

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

The pigment 6,6′-dibromoindigo (Tyrian purple) shows strong intermolecular hydrogen bonds and the film formation is, therefore, expected to be influenced by the polar character of the substrate surface. Thin films of Tyrian purple were prepared by physical vapor deposition on a variety of substrates with different surface energies: from highly polar silicon dioxide surfaces to hydrophobic polymer surfaces. The crystallographic properties were investigated by X-ray diffraction techniques such as X-ray reflectivity and grazing incidence X-ray diffraction. In all cases, crystallites with "standing" molecules relative to the substrate surface were observed independently of the substrate surface energy. In the case of polymer surfaces, additional crystallites are formed containing "lying" molecules with their aromatic planes parallel to the substrate surface. Small differences in the crystallographic lattice constants were observed as a function of substrate surface energy, the corresponding small changes in the molecular packing are explained by a variation of the hydrogen bond geometries. This work reveals that despite the limited influence of the surface energy on the molecular orientation, the crystalline packing of Tyrian purple within thin films is altered and slightly different structures form.

Original languageEnglish
Pages (from-to)73-79
Number of pages7
JournalJournal of Crystal Growth
Volume447
DOIs
Publication statusPublished - 1 Aug 2016

Keywords

  • A1. Polymorphism
  • A1. X-ray diffraction
  • A3. Organic thin films
  • B1. Hydrogen-bonded pigments

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Materials Chemistry
  • Inorganic Chemistry

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