Extended Conjugated Donor-Acceptor Molecules with E-(1,2-Difluorovinyl) and Diketopyrrolopyrrole ( DPP) Moieties toward High-Performance Ambipolar Organic Semiconductors

Two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A) conjugated molecules, DPP-F and DPP-2F, which contain E-(1,2-difluorovinyl) moieties, are reported. The LUMO energies of DPP-F and DPP-2F were estimated to be -3.49 and -3.70 eV, respectively, based on their redox potentials and absorption spectral data; these values were clearly lowered because of the incorporation of electron-withdrawing E-(1,2-difluorovinyl) moieties. Organic field-effect transistors (OFETs) with thin films of DPP-F and DPP-2F were successfully fabricated with conventional techniques. Based on the respective transfer and output characteristics measured in an inert atmosphere, thin films of DPP-2F display ambipolar semiconducting behavior with hole and electron mobilities reaching 0.42 and 0.80 cm(2)V(-1)s(-1), respectively. The as-prepared OFET of DPP-2F already shows high hole and electron mobilities that are not influenced remarkably by thermal annealing. For thin films of DPP-F, only p-type semiconducting behavior was observed in both an inert atmosphere and air, and the hole mobility increased to 0.1 cm(2)V(-1)s(-1) after thermal annealing. XRD and AFM studies were performed with thin films of DPP-F and DPP-2F after annealing at different temperatures.