Two new copolymers, poly [fluorene-co-alpha-dithieno[3,2-b:2',3'-d]thiophene] (PFDTT-alpha) and poly [fluorene-co-beta-dithieno[3,2-b:2',3'-d]thiophene] (PFDTT-beta) were synthesized through the Suzuki coupling reaction, where dithieno[3,2-b:2',3'-d]thiophene (DTT) was introduced into the backbones of polyfluorenes by two different linkage styles, which distinctively tuned HOMO/LUMO levels of the copolymers and the effective conjugation length.