title: Polymorphic Phase-Dependent Optical and Electrical Properties of a Diketopyrrolopyrrole-Based Small Molecule.
abstract: 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.
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Shabi
authors.initials: S
authors.lastname: Thankaraj Salammal
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Zhongqiang
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Jiehuan
authors.initials: J
authors.lastname: Chen
authors.affiliation: Faculte des Sciences, Laboratoire Chimie des Polymeres, Universite Libre de Bruxelles , CP 206/1, Boulevard du Triomphe, 1050 Bruxelles, Belgium.
authors.forename: Basab
authors.initials: B
authors.lastname: Chattopadhyay
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Jiake
authors.initials: J
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Lei
authors.initials: L
authors.lastname: Fu
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Congcheng
authors.initials: C
authors.lastname: Fan
authors.affiliation: State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, P. R. China.
authors.forename: Hongzheng
authors.initials: H
authors.lastname: Chen
keywords: diketopyrrolopyrrole; optical and electrical properties; organic electronics; polymorphism; π−π stacking