Synthesis of 1,4-dihydropyrrolo[3,2-b]pyrrole-containing donor-acceptor copolymers and their optoelectronic properties

Donor-acceptor (D-A)-conjugated polymers have achieved promising performance metrics in numerous optoelectronic applications that continue to motivate studying structure-property relationships and discovering new materials. Here, the materials toolbox is expanded by synthesizing D-A copolymers where 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) is directly incorporated into the main chain of D-A copolymers for the first time via direct heteroarylation polymerization. Notably, the synthetic complexity of DHPP-containing polymers coupled with thieno[3,2-b]pyrrole-4,6-dione (TPD) or 3,6-bis(2-thienyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Th2DPP) comonomers is calculated to be lower compared to many common conjugated polymers synthesized via direct arylation. The electron-rich nature of DHPPs when coupled with TPD or DPP enables optoelectronic properties to be manipulated, evident by measuring distinctly different absorbance and redox properties. Additionally, these D-A copolymers demonstrate their potential in organic electronic applications, such as electrochromics and organic photovoltaics. The reported DHPP-alt-Th2DPP copolymer is the first DHPP-based colored-to-transmissive electrochrome and achieves power conversion efficiencies of similar to 2.5% when incorporated into bulk heterojunction solar cells. Overall, the synthetic accessibility of DHPP monomers and their propensity to participate in robust polymerizations highlights the value of establishing structure-property relationships of an under-utilized scaffold. These fundamental attributes serve to inform and advance efforts in the development of DHPP-containing copolymers for various applications.