Tuning the Semiconducting Behaviors of New Alternating Dithienyldiketopyrrolopyrrole–Azulene Conjugated Polymers by Varying the Linking Positions of Azulene

Abstract

Three new conjugated polymers <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> with dithienyldiketopyrrolopyrrole (DPP) and azulene moieties were synthesized and characterized. The five-membered rings of azulene are connected with DPP in <b>DPPA1</b> and <b>DPPA2</b>, whereas the seven-membered ring of azulene is incorporated into the backbone of <b>DPPA3</b>. The LUMO energy of <b>DPPA3</b>, which was determined on the basis of the respective cyclic voltammograms and absorption spectra, is lower than those of <b>DPPA1</b> and <b>DPPA2</b>. OFETs were successfully fabricated with thin films of <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b>. Thin films of <b>DPPA1</b> and <b>DPPA2</b> 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 <b>DPPA3</b> 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 <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> can be tuned by varying the linkage positions of azulene with DPP moieties. Furthermore, <b>DPPA1</b>, <b>DPPA2</b>, and <b>DPPA3</b> were tested preliminarily as photovoltaic materials. The power conversion efficiency (PCE) reaches 2.04% for the blending thin film <b>DPPA1</b> with PC₇₁BM