Tuning the semiconducting behaviors of new alternating dithienyldiketopyrrolopyrrole-azulene conjugated polymers by varying the linking positions of azulene

Three new conjugated polymers DPPA1, DPPA2, and DPPA3 with dithienyldiketopyrrolopyrrole (DPP) and azulene moieties were synthesized and characterized. The five-membered rings of azulene are connected with DPP in DPPA1 and DPPA2, whereas the seven-membered ring of azulene is incorporated into the backbone of DPPA3. The LUMO energy of DPPA3, which was determined on the basis of the respective cyclic voltammograms and absorption spectra, is lower than those of DPPA1 and DPPA2. OFETs were successfully fabricated with thin films of DPPA1, DPPA2, and DPPA3. Thin films of DPPA1 and DPPA2 exhibit p-type semiconducting properties with hole mobilities up to 0.97 cm² V^-1 s^-1, whereas typical ambipolar behavior is found for thin film of DPPA3 with hole and electron mobilities reaching 0.062 cm² V^-1 s^-1 and 0.021 cm² V^-1 s^-1, respectively. The results reveal that semiconducting properties of DPPA1, DPPA2, and DPPA3 can be tuned by varying the linkage positions of azulene with DPP moieties. Furthermore, DPPA1, DPPA2, and DPPA3 were tested preliminarily as photovoltaic materials. The power conversion efficiency (PCE) reaches 2.04% for the blending thin film DPPA1 with PC₇₁BM.