A series of aromatic organic molecules functionalized with different halogen atoms (I/ Br), motion-capable groups (olefin, azo or imine) and molecular length were designed and synthesized. The molecules self-assemble in the solid state through halogen bonding and exhibit molecular packing sustained by either herringbone or face-to-face π-stacking, two common motifs in organic semiconductor molecules. Interestingly, dynamic pedal motion is only achieved in solids with herringbone packing. On average, solids with herringbone packing exhibit larger thermal expansion within the halogen-bonded sheets due to motion occurrence and molecular twisting, whereas molecules with face-to-face π-stacking do not undergo motion or twisting. Thermal expansion along the π-stacked direction is surprisingly similar, but slightly larger for the face-to-face π-stacked solids due to larger changes in π-stacking distances with temperature changes. The results speak to the importance of crystal packing and intermolecular interaction strength when designing aromatic-based solids for organic electronics applications.
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This content will become publicly available on March 20, 2025
Polymorphism and π Stacking Affect Thermal Expansion Behavior in Halogen-Bonded Cocrystals Based on 1,4-Diiodoperchlorobenzene
The thermal expansion behavior of a series of halogen-bonded cocrystals containing 1,4-diiodoperchlorobenzene as the donor is described. Two of the solids are polymorphs and contain 4-stilbazole as the acceptor, while the third solid contains 4-(phenylethynyl)pyridine as the acceptor, and this solid is isostructural with one of the polymorphs. All solids are sustained by I···N halogen bonds, and the least thermal expansion occurs along this direction in all solids. The polymorphs exhibit significant differences in π stacking, and we show that electronically similar face-to-face stacked rings undergo more expansion compared to electronically different stacked rings. Moreover, in the two polymorphs, the directions of moderate expansion and most expansion are reversed, demonstrating how cocrystal polymorphism can affect material properties.
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- Award ID(s):
- 2411677
- NSF-PAR ID:
- 10496507
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- Crystal Growth & Design
- Volume:
- 24
- Issue:
- 6
- ISSN:
- 1528-7483
- Page Range / eLocation ID:
- 2468-2474
- Subject(s) / Keyword(s):
- ["Aromatic compounds","Hydrocarbons","Molecular interactions"]
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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