Bifuran- and bithiophene-fused 4,6-dihydro-1,2,7-oxadiborepins as building blocks for conjugated copolymers

The use of dithieno- (DTDB) and difuro-4,6-dihydro-1,2,7-oxadiborepins (DFDB) as components of conjugated copolymers is demonstrated. Building upon our recently developed protocol for the modular synthesis of 5,5’-dibrominated difuro-4,6-dihydro-1,2,7-oxa- and azadiborepins, we devised a scalable route to the corresponding 5,5’-dibrominated and 5,5’-distannylated DTDB derivatives, which serve as monomers for subsequent polymerizations. Combining both the difunctionalized DTDB- and the DFDB-based monomers with electron-rich benzodithiophene (BDT) and electron-poor diketopyrrolopyrrole (DPP) building blocks, respectively, gave four new copolymers, which are well-soluble and fully air- and moisture-stable. They show broad absorptions over the visible spectral range – with the bands of the DPP-containing copolymers extending into the near-IR region. DFT calculations give further insights into the electronics of the copolymers. Photoelectrochemical measurements revealed that three of the new copolymers exhibit p-type while one of them exhibits n-type semiconducting behavior.