Design of Functional Disorder in Charge-Transfer Cocrystals.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Crystallographic disorder is often viewed as a defect in molecular crystals.
• However, phenomena like dielectricity and ferroelectricity depend on solid-state molecular motion.
• This motion can be indicated by crystallographic disorder, suggesting potential utility.

Purpose of the Study:

• To explore the dynamics, electronic performance, and origin of whole-molecule disorder in a model charge-transfer (CT) cocrystal (DMDBS-DDQ).
• To investigate the energetics underlying functional disorder for design guidelines in molecular crystals.
• To challenge existing design principles for functional disorder.

Main Methods:

• Investigation of a model charge-transfer cocrystal, DMDBS-DDQ, selected from the Cambridge Structural Database (CSD).
• Preparation of DMDBS-DDQ via single-crystal-to-single-crystal desolvation.
• Analysis of electrical performance and anisotropic thermal expansion behavior.

Main Results:

• The electrical performance and thermal expansion of DMDBS-DDQ are consistent with in-plane dynamic disorder above 33 °C (306 K).
• The cocrystal does not follow previous design principles that target size-mismatched coformers for void/cavity space.
• Findings suggest dynamic disorder is governed by short-range intermolecular interactions.

Conclusions:

• Dynamic disorder in molecular crystals can be harnessed for electronic functionality.
• Design strategies for functional disorder should prioritize short-range intermolecular interactions over void space.
• This work provides new insights into the energetics governing functional disorder in molecular systems.