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

The realization of pi-deficient acceptors and their donor-acceptor copolymers has become a key research focus for the realization ofversatile organic optoelectronicmaterials and devices. Herein, wedemonstrate the theoretical design, synthesis, and physicochemical/optoelectronic characterization of two meso-pi-extended/deficient BOD-IPY building blocks (2OD-T2BDYand2OD-TTzBDY) and a library ofdonor-acceptor copolymers with low band gap (Eg= 1.30-1.35 eV)based on these building blocks. These building blocks, to the best of ourknowledge, are thefirst examples of BODIPYs with meso-pi-extension. Alibrary of BODIPY building blocks with varied meso units/substituents isstudied to reveal the meso effects on the semiconducting BODIPY'soptoelectronic properties. The building blocks showed favorable pi-acceptor electronic/structural properties with meso-pi-delocalized andstabilized LUMOs (ca.-3.6 eV) and large ground-state dipole momentsof 4.9-5.5 D. Consistent with the theoretical/experimental pi-electronic structures, all copolymers functioned asp-typesemiconductors infield-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversionefficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm-2were achieved. This study demonstrates a unique meso-pi-extension strategy to realize BODIPYs with favorable pi-acceptor properties, and ourfindings could open up future materials designavenues in various organic optoelectronic applications.