Polymorphic Phase-Dependent Optical and Electrical Properties of a Diketopyrrolopyrrole-Based Small Molecule
journal contributionposted on 19.07.2016 by Shabi Thankaraj Salammal, Zhongqiang Zhang, Jiehuan Chen, Basab Chattopadhyay, Jiake Wu, Lei Fu, Congcheng Fan, Hongzheng Chen
Any type of content formally published in an academic journal, usually following a peer-review process.
Four different polymorphic conformations of diethyl 5,5′-[5,5′-[2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl]bis(thiophene-5,2-diyl)]difuran-2-carboxylate (DPP-(CF)2), namely, DPP-(CF)2-α, DPP-(CF)2-β, DPP-(CF)2-γ, and DPP-(CF)2-ω, were identified from X-ray diffraction analysis conducted on their thin films and single crystals. Highly crystalline and well-textured thin films of these four polymorphs were successfully prepared via postgrowth solvent vapor and thermal annealing treatments to investigate the polymorphic phase-dependent optical and electrical properties of DPP-(CF)2. Interestingly, during the phase transition from DPP-(CF)2-α to DPP-(CF)2-ω, the optical band gap decreases from 1.75 to 1.5 eV because of the enhanced π–π interaction between the neighboring molecules. Except for DPP-(CF)2-γ, the other three phases show ambipolar charge transport. Although DPP-(CF)2-β and DPP-(CF)2-γ exhibit a similar way of packing, a small increment in the π–π-stacking distance (0.006 Å) and twist conformation of the grafted electron-donating moieties of DPP-(CF)2-γ are found to reduce its hole mobility.