Acceptor-donor-acceptor conjugated oligomers based on diketopyrrolopyrrole and thienoacenes with four, five and six rings for organic thin-film transistors

Three acceptor-donor-acceptor (A-D-A) conjugated oligomers, i.e., O1, O2 and O3, have been synthesized using diketopyrrolopyrrole (DPP) as an electron-acceptor unit, and naphtho[1,2-b:5,6-b’]dithiophene (NDT), anthra[1,2-b:5,6-b’]dithiophene (ADT) or dithieno[3,2-b:3’,2’-b’]naphtho[1,2-b:5,6-b’]dithiophene (DTNDT) as electron-donor unit. These oligomers exhibit identical highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, which were ca. −5.1 and −3.3 eV, respectively. Upon thermal annealing, all three oligomers formed thin films with ordered microstructures, and their organic thin film transistors (OTFTs) exhibited p-type transport behavior. The mobility was increased with an extension of the size of D-units. O3 showed the best OTFT performance with the mobility of up to 0.20 cm2·V−1·s−1. The film quality of O3 was improved by adding 1 wt% poly(methylmethacrylate) (PMMA). In consequence, the mobility of the O3-based devices was further enhanced to 0.30 cm2·V−1·s−1.