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 cm 2 V −1 s −1 , whereas typical ambipolar behavior is found for thin film of DPPA3 with hole and electron mobilities reaching 0.062 cm 2 V −1 s −1 and 0.021 cm 2 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 PC 71 BM.
■ INTRODUCTIONIn recent years, alternating conjugated electron donor (D)− acceptor (A) polymers have received increasing attention because they behave as solution-processable semiconductors, which promise for applications in low-cost, large-area, and flexible electronic devices, such as field effect transistors (FETs), photovoltaics (PVs), and light-emitting diodes (LEDs). 1−3 Various electron donors and acceptors were selected to construct conjugated D−A polymers for developing semiconducting materials of high performance. 4 Among them, dithienyldiketopyrrolopyrrole (DPP) has been intensively investigated as electron accepting moiety to build conjugated D−A polymers. 5 For instance, Liu, Ong, and co-workers reported the DPP−thieno[3,2-b]thiophene conjugated polymer exhibiting p-type semiconducting property with hole mobility up to 10.5 cm 2 V −1 s −1 . 6 Meanwhile, DPP−selenophene alternating conjugated polymers were found to behave as ambipolar semiconductors with hole and electron mobilities reaching 8.84 cm 2 V −1 s −1 and 4.34 cm 2 V −1 s −1 , respectively. 7 Apart from DPP, other electron-accepting moieties including naphthalenediimide, 8 isoindigo, 9 benzothiadiazole, 10 and Pechmann dye 11 were also linked to various electron donors to yield the respective semiconducting D−A polymers.Heterocycles and fused heterocycles such as thiophene and thieno[3,2-b]thiophene were widely employed as electron donors in these semiconducting D−A polymers. 5,6,12 In comparison, conjugated D−A polymers with aromatic hydrocarbons as electron donors were less intensively studied. 13 In this paper, we report three conjugated D−A polymers DPPA1, DPPA2, and DPPA3 entailing DPP and azulene moieties (Scheme 1). The selection of azulene is based on the following considerations: (i) azulene is a resonance-stabilized nonalternant aromatic hydrocarbon with an el...