Segregated versus Mixed Interchain Stacking in Highly Oriented Films of Naphthalene Diimide Bithiophene Copolymers
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- 作者：Martin Brinkmann ; Eric Gonthier ; St茅fan Bogen ; Kim Tremel ; Sabine Ludwigs ; Martin Hufnagel ; Michael Sommer
- 刊名：ACS Nano
- 出版年：2012
- 出版时间：November 27, 2012
- 年：2012
- 卷：6
- 期：11
- 页码：10319-10326
- 全文大小：467K
- 年卷期：v.6,no.11(November 27, 2012)
- ISSN：1936-086X
文摘
Highly oriented films of an electron accepting polymer semiconductor, poly{[N,N鈥?bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5鈥?(2,2鈥?bithiophene)} (PNDI2OD-T2), are obtained by two different methods, namely directional epitaxial crystallization (DEC) on 1,3,5-trichlorobenzene (TCB) and epitaxy on friction transferred poly(tetrafluoroethylene) (PTFE) substrates. Two distinct polymorphs with unprecedented intrachain resolution are identified by high-resolution transmission electron microscopy (HR-TEM). Form I is obtained by DEC on TCB, whereas highly oriented films of form II are obtained on PTFE substrates after melting at T = 300 掳C and cooling at 0.5 K/min. In form I, both electron diffraction and HR-TEM indicate a segregated stacking of bithiophene (T2) and naphthalene diimide (NDI) units forming separate columns. In form II, a c/2 shift between successive 蟺-stacked chains leads to mixed 蟺-overlaps of T2 and NDI. Form I can be transformed into form II by annealing at T > 250 掳C. The different 蟺-stacking of NDI and T2 in the two polymorphs have characteristic signatures in the UV鈥搗is spectra, especially in the charge transfer band around 750 nm which is also observed in spin-coated films.