Research Highlights

The performance of organic semiconductors depends both on their molecular structure, and on how the molecules aggregate into solids via crystallization.

However, while current chemistry can reliably determine the effects of molecular structure on performance, it has a harder time predicting the effects of molecular aggregation that must account for both weak intermolecular forces and irregular molecular shapes.

A 2023 article by Takimiya and co-workers from AIMR addressed this gap by interrogating how the introduction of methylthiolate functional groups at specific positions on parent molecules affects both their aggregation and their semiconducting properties¹.

“Previously, we had found that the introduction of methylthio groups at the benzodithiophene molecule β-positions changed the aggregation from the herringbone structure of the parent molecule to the π-stacking structure,” explains Takimiya. “Here, we tested whether this approach on acene-type parent molecules can also crystallize into structures with higher π-π interactions.”

To this end, the team synthesized four anthracene and tetracene compounds at various extents of methylthiolation, and used single-crystal X-ray analysis and single-crystal field-effect transistors to measure the product crystal structures and transport properties, respectively.

“Our results showed that methylthio groups can also be used to change the crystal structure from the herringbone structure of the parent acenes to different π-stacking structures of the products—enhancing both intermolecular π-π interactions and transport properties” says Takimiya. “This suggests our approach could be adapted for other rigid, planar molecules.”

The team now aims to gather new experimental data exemplified above to leverage future, more powerful quantum-chemical simulations towards predicting the effects of molecular aggregation on product-crystal properties.

(Author: Patrick Han)