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

Abstract

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...

Application of Azulene in Constructing Organic Optoelectronic Materials: New Tricks for an Old Dog

“…The construction of alternating donor (D)–acceptor (A) structures might afford high‐performance semiconducting polymers. Three azulene‐containing conjugated D–A polymers, 30 a – c (Figure ), with dithienyldiketopyrrolopyrrole units were reported by Zhang and co‐workers . It was demonstrated that the semiconducting behavior of these three polymers can be modulated by altering the connectivity of the azulene units in the polymer backbones.…”

“…This is consistent with a previous study on the modulation of optoelectronic and stimuli‐responsive properties of azulene‐based polymers by tuning the connecting positions of azulene moieties in the polymeric main chain . For polymers 30 a and 30 b , in which the azulene moieties were connected at electron‐rich five‐membered rings, their OFET devices exhibited unipolar p‐type semiconducting properties with hole mobilities of 0.97 and 8×10 −2 cm 2 V −1 s −1 , respectively . In comparison with 30 a and 30 b , 30 c with the electron‐deficient seven‐membered ring of azulene incorporated into the polymeric backbone has a lower LUMO energy as well as a better spread LUMO density, demonstrating ambipolar semiconducting behavior with hole and electron mobilities of up to 6.2×10 −2 and 2.1×10 −2 cm 2 V −1 s −1 , respectively …”

Tuning the optoelectronic properties of dual-acceptor based low-bandgap ambipolar polymers by changing the thiophene-bridge length

“…18 Another ligand, tri(o-tolyl)phosphine (P(o-tol)3) was also attempted to prepare PDPP-T-TQ as it was reported that polymers with Mn higher than 10 kg mol -1 could be produced when using the Pd2(dba)3/P(o-tol)3 catalyst system in Suzuki coupling based on DPPdiboronic ester. [23][24][25] The Mn of resulting polymer (6.3 Kg mol -1 , PDI: 2.9) is however slightly lower in comparison with that using the ligand of (t-Bu)3P·HBF4. After introducing one more electron-rich thiophene onto monomer 4 at both sides, the steric hindrance between DPP and monomer 7 was reduced so that the PDPP-3T-TQ possessed a higher Mn than the other two polymers.…”

An Azulene‐Containing Low Bandgap Small Molecule for Organic Photovoltaics with High Open‐Circuit Voltage

“…In view of the easy availability and low cost of some azulene derivatives, it is reasonable to speculate that azulene might be a simple but promising D structural unit to construct OPV donor materials with low bandgaps, high V oc and good hole mobilities. However, up until now, there have only been two relative reports on azulene‐containing OPV polymers . Although plenty of azulene‐based small molecules have been reported, to the best of our knowledge, hitherto none have been applied to the OPV field.…”