Side-Chain Length Matching Enhances Aggregation and Crystallization in Conjugated Polymers

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Side-chain engineering is crucial for tailoring conjugated polymer microstructure and optimizing device performance.
• A common challenge is the solubility-crystallinity trade-off influenced by side-chain length.
• Understanding structure-property relationships is key for advancing organic electronics.

Purpose of the Study:

• To investigate the anomalous side-chain length dependency of aggregation and crystallization in diketopyrrolopyrrole-thieno[3,2-b]thiophene (PDPPTT-Cx) copolymers.
• To elucidate the mechanism behind the observed structure-property relationships.
• To provide guidance for precise side-chain engineering in high-performance organic electronic materials.

Main Methods:

• Synthesis and characterization of PDPPTT-Cx copolymers with varying side-chain lengths (x = 5-12).
• Solution-state aggregation and solid-state crystallization studies.
• First-principles modeling and calculations to understand intermolecular interactions.

Main Results:

• Anomalous side-chain length dependency observed, deviating from the typical solubility-crystallinity trade-off.
• Intermediate side-chain lengths (x = 7-9), particularly PDPPTT-C8, exhibited enhanced solution-state aggregation and solid-state crystallinity.
• PDPPTT-C8 achieved significantly higher hole mobility (0.091 cm² V⁻¹ s⁻¹) and conductivity (10.3 S cm⁻¹) after doping compared to analogues.

Conclusions:

• Side-chain length matching effect maximizes interchain contact and van der Waals interactions, enhancing polymer packing.
• Precise side-chain engineering in PDPPTT-Cx copolymers can lead to superior charge transport properties.
• Findings offer valuable insights for designing high-performance conjugated polymers for organic electronics.