title: Donor-Acceptor Copolymers Based on Thermally Cleavable Indigo, Isoindigo, and DPP Units: Synthesis, Field Effect Transistors, and Polymer Solar Cells.
abstract: A series of donor-acceptor type of π-conjugated copolymers based on tert-butoxycarbonyl (t-Boc) substituted indigo, isoindigo or diketopyrrolopyrrole as the acceptor unit and a benzodithiophene derivative as the donor unit was designed and synthesized. These copolymers can be readily dissolved in organic solvents and can produce uniform films by solution deposition. Thermal treatment of copolymer films at 200 °C for 10 min resulted in elimination of t-Boc side groups in nearly quantitative yield as suggested by thermogravimetric analysis and Fourier transform infrared spectroscopy. The elimination of the bulky t-Boc side groups resulted in the emergence of N-H···O═C hydrogen bonding interactions by virtue of the lactam structures of the indigo, isoindigo and diketopyrrolopyrrole units. Of particular interests is the distinctly increased field-effect mobility of these copolymers after thermal treatment, which may arise from the enhanced coplanarity and intermolecular ordering of the indigo, isoindigo or diketopyrrolopyrrole units after elimination of the bulky t-Boc side groups. These results demonstrate that the incorporation of latent side groups provides a viable strategy to construct conjugated polymers that can attain more ordered intermolecular stacking by simple thermal treatments. On the other hand, despite the thermal cleavage of t-Boc groups can also lead to increased ordering of polymer chains when blending with [6,6]-phenyl C71 butyric acid methyl ester, the photovoltaic performances of the resulting bulk heterojunction solar cells did not obviously increase due to the serious phase separation and coarsening of the film morphology.
authors: Chunchen
authors: C
authors: Liu
authors: Sheng
authors: S
authors: Dong
authors: Ping
authors: P
authors: Cai
authors: Peng
authors: P
authors: Liu
authors: Shengjian
authors: S
authors: Liu
authors: Junwu
authors: J
authors: Chen
authors: ‡Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States.
authors: Feng
authors: F
authors: Liu
authors: Lei
authors: L
authors: Ying
authors: ‡Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States.
authors: Thomas P
authors: TP
authors: Russell
authors: Fei
authors: F
authors: Huang
authors: Yong
authors: Y
authors: Cao
keywords: conjugated polymers; hydrogen bonding; intermolecular ordering; organic field-effect transistor; polymer solar cell; thermal cleavage