Conjugated Polymers Based on a New Building Block: Dithienophthalimide

A new fused-ring building block dithieno[3,2- f:2′,3′- h ]phthalimide was synthesized and used in synthesis of conjugated polymers. On the basis of this building block, we designed and synthesized a series of conjugated copolymers containing electron-rich unit benzo[1,2- b:4,5- b ′]dithiophene ( P1 and P2 ) or with electron-deficient unit 2,2′ - bithiazole ( P3 and P4 ) or benzo[ c ][1,2,5]thiadiazole ( P5 ) and homopolymer ( P6 ). P1 and P4 – P6 have good solubility in common organic solvents, while P2 and P3 have poor solubility. P1 – P6 exhibit good thermal stability with 5% weight loss temperatures of 193–417 °C. P1 – P6 in films exhibit absorption maxima of 482–532 nm with optical bandgaps of 1.88–2.25 eV and weak emission peaked at 597–721 nm. P1 – P6 have estimated HOMOs of −5.3 to −6.2 eV and LUMOs of −2.8 to −3.4 eV. The optical properties and HOMO/LUMO levels are influenced by the comonomers. The polymer solar cells based on P1:PC 61 BM (1:1, w/w) exhibit preliminary power conversion efficiency of 0.30% under an AM 1.5 simulated solar light at 100 mW/cm 2 .