π-Conjugated polymers (CPs) are highly promising semiconducting materials used in various organic electronic devices. To synthesize CPs efficiently with high level of atom- and step-economy, direct arylation polymerization (DArP) has been an attractive method. However, traditional catalytic systems used in DArP required high reaction temperatures, leading to the formration of structural defects and limited performance of the polymers.
Herein, we report the development of a novel Pd/Ag dual-catalytic system, based on Ag-mediated concerted metalation-deprotonation (CMD) process under mild reaction conditions to bring a broad scope and suppressed structural defects.
First, we revealed the dual-catalytic system can facilitate the cross-coupling between C-H and C-Br substrates with significantly decreased homo-coupling products, benefited from the high intrinsic chemoselectivity and mild reaction conditions. Next, by expanding this to several acceptor C-H monomers with C-Br coupling partners, we attained various CPs with D-A and A-A compositions at moderate temperatures (from 60 to 70 ^oC). This approach enabled polymerization using various acceptor building blocks, widely used for high-performance organic electronic devices, such as thieno[3,2-b]pyrrole-4,6-dione (TPD), octafluorobiphenyl (F₈Ph₂), 2,2’-bithiazole (biTz), and 3,4-dicyanothiophene (CN₂Th). Additionally, this process operates in sustainable solvents, further improving the environmental friendliness of this system.
Also, the optical properties and crystallinity of polymers were improved by the enhanced structural regularity. Several spectroscopic analysis provided substantiating evidences for the low structural defects, such as higher Huang-Rhys factor and crystallinity. This implies the Pd/Ag DArP can provide superior performance for electronic devices, compared to conventional DArP based on Pd catalysis.
These findings would contribute to the establishment of a general platform to simultaneously enhance the economic feasibility and performance of organic electronic materials.

Tae-Lim Choi

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