Aldol Polymerization to Construct Half-Fused Semiconducting Polymers

Conventional conjugated polymer synthesis involves costly transition-metal catalysts and even toxic reagents, causing serious environmental challenges around the world. The comonomer linkages of semiconducting polymers are mostly single bonds; charge delocalization and transport have been hindered due to rotation around these single bonds, leading to energetic and conformational disorders. Here, we have developed a novel programmable half-fused polymer library by introducing aldehyde chemistry to promote a very simple and cheap Lewis acid-mediated aldol condensation that affords conjugated polymers with continuous double bonds and single bonds as the linkages between the polymer repeat units, maintaining a coplanar conjugated backbone to eliminate rotation owing to the intramolecular noncovalent interactions. In addition, this innovative concept not only shows an excellent substrate generality but also affords unprecedented polymers with unique properties, allowing us to change the variable conjugated length and side-chain engineering of the backbone to modulate the optoelectronic properties and tune the delocalization of frontier molecular orbitals. These polymers also exhibit very high number-averaged molecular weights (Mn) while showing good solution processability, which makes them applicable as high-performance thin-film transistor materials with reduced conformational disorder. Herein, our results demonstrate that the half-fused design strategy can effectively extend the scope of semiconducting polymers. The low synthetic complexity can be utilized to design organic electronic materials for large-scale production and commercialization.