Abstract
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.
Highlights
Thermal expansion (TE) is a fundamental property of materials, and it describes the response to temperature change (Yao et al, 2019; Saha, 2017)
We demonstrate the comprehensive influence of crystal packing motion and noncovalent interaction strength on TE behaviors in stacked solids
We expected the stronger IÁ Á ÁI interactions to be less affected by temperature changes, while BrÁ Á ÁBr interactions are weaker and should be more affected
Summary
Thermal expansion (TE) is a fundamental property of materials, and it describes the response to temperature change (Yao et al, 2019; Saha, 2017). Halogen bonds have been used to control solid-state packing in organic semiconductor-based materials and improve device performance (Wilson et al, 2015; Weldeab et al, 2018; Zhang & Wang, 2021; Li et al, 2018). Our group demonstrated that dynamic pedal motion leads to large PTE in organic solids (Hutchins et al, 2018; Juneja et al, 2019; Ding et al, 2020). We demonstrate that the molecules crystallize into packing arrangements analogous to those frequently observed in organic semiconductor materials, herringbone or face-to-face -stacked [Fig. 1(b)]. We demonstrate the comprehensive influence of crystal packing motion and noncovalent interaction strength on TE behaviors in stacked solids
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