Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
SHR Neuro Krebs Kardio Lipid Stoffw Microb
Truger, M; Roscioni, OM; Röthel, C; Kriegner, D; Simbrunner, C; Ahmed, R; Głowacki, ED; Simbrunner, J; Salzmann, I; Coclite, AM; Jones, AO; Resel, R.
Surface-Induced Phase of Tyrian Purple (6,6'-Dibromoindigo): Thin Film Formation and Stability.
Cryst Growth Des. 2016; 16(7):3647-3655
Doi: 10.1021/acs.cgd.6b00104
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- Co-Autor*innen der Med Uni Graz
- Simbrunner Josef
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- Abstract:
- The appearance of surface-induced phases of molecular crystals is a frequently observed phenomenon in organic electronics. However, despite their fundamental importance, the origin of such phases is not yet fully resolved. The organic molecule 6,6'-dibromoindigo (Tyrian purple) forms two polymorphs within thin films. At growth temperatures of 150 °C, the well-known bulk structure forms, while at a substrate temperature of 50 °C, a surface-induced phase is observed instead. In the present work, the crystal structure of the surface-induced polymorph is solved by a combined experimental and theoretical approach using grazing incidence X-ray diffraction and molecular dynamics simulations. A comparison of both phases reveals that π-π stacking and hydrogen bonds are common motifs for the intermolecular packing. In-situ temperature studies reveal a phase transition from the surface-induced phase to the bulk phase at a temperature of 210 °C; the irreversibility of the transition indicates that the surface-induced phase is metastable. The crystallization behavior is investigated ex-situ starting from the sub-monolayer regime up to a nominal thickness of 9 nm using two different silicon oxide surfaces; island formation is observed together with a slight variation of the crystal structure. This work shows that surface-induced phases not only appear for compounds with weak, isotropic van der Waals bonds, but also for molecules exhibiting strong and highly directional hydrogen bonds.