Meso-π-Extended/Deficient BODIPYs and Low-Band-Gap Donor–Acceptor Copolymers for Organic Optoelectronics

The realization of π-deficient acceptors and their donor–acceptor copolymers has become a key research focus for the realization of versatile organic optoelectronic materials and devices. Herein, we demonstrate the theoretical design, synthesis, and physicochemical/optoelectronic characterization of two meso-π-extended/deficient BODIPY building blocks (2OD–T2BDY and 2OD–TTzBDY) and a library of donor–acceptor copolymers with low band gap (Eg = 1.30–1.35 eV) based on these building blocks. These building blocks, to the best of our knowledge, are the first examples of BODIPYs with meso-π-extension. A library of BODIPY building blocks with varied meso units/substituents is studied to reveal the meso effects on the semiconducting BODIPY's optoelectronic properties. The building blocks showed favorable π-acceptor electronic/structural properties with meso-π-delocalized and stabilized LUMOs (ca. −3.6 eV) and large ground-state dipole moments of 4.9–5.5 D. Consistent with the theoretical/experimental π-electronic structures, all copolymers functioned as p-type semiconductors in field-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversion efficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm–2 were achieved. This study demonstrates a unique meso-π-extension strategy to realize BODIPYs with favorable π-acceptor properties, and our findings could open up future materials design avenues in various organic optoelectronic applications.