Effects of Replacement on the Optical Properties of Narrow Bandgap Polymers: Comparing the Difference Between Thieno[3,2-b]thiophene Units and Thiophene Units

The effects of replacement on the optical properties of diketopyrrolopyrrole(DPP)-based polymers are discussed through replacing the thieno[3,2-b]thiophene units by thiophene units. It is easy to see that the role of re-placement would lead to blue shift of steady-state absorption spectrum when thieno[3,2-b]thiophene units is replaced by thiophene units. Meanwhile, the transient absorption data indicate that the role of replacement would not change the relaxation mechanism of polymer, but is able to adjust the photo-excitation relaxation rate of polymer. Their in-tensity-dependent dynamic curves show that the exciton-exciton annihilation(EEA) would participate in the relaxation process when the polymer is in the aggregation. Through comparing the EEA data between the polymers, it is found that the role of replacement would change the spatial distribution of exciton.