Surface-Induced Phase of Tyrian Purple (6,6'-Dibromoindigo): Thin Film Formation and Stability
| Autor: | Magdalena, Truger, Otello M, Roscioni, Christian, Röthel, Dominik, Kriegner, Clemens, Simbrunner, Rizwan, Ahmed, Eric D, Głowacki, Josef, Simbrunner, Ingo, Salzmann, Anna Maria, Coclite, Andrew O F, Jones, Roland, Resel |
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| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | Crystal Growth & Design |
| ISSN: | 1528-7483 |
| Popis: | 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. A surface induced crystal structure of the hydrogen-bonded pigment Tyrian purple (6,6′-dibromoindigo) is found in thin films. The structure is metastable and shows an irreversible phase transition to the stable bulk phase at a temperature of 210 °C. The molecular packing of both phases has the aromatic π−π stacking as a common motif but forms different hydrogen bond networks. |
| Databáze: | OpenAIRE |
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