Diketopyrrolopyrrole Organic Thin-Film Transistors: Impact of Alkyl Substituents and Tolerance of Ethylhexyl Stereoisomers

Matthias Stolte, Sabin Lucian Suraru, Patricia Diemer, Tao He, Christian Burschka, Ute Zschieschang, Hagen Klauk, Frank Würthner

Research output: Contribution to journalArticlepeer-review

40 Scopus citations

Abstract

Bis(thiophen-2-yl)-diketopyrrolopyrrole (DPP) dyes bearing various alkyl substituents at the amide positions (n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl) and chlorine (Cl), bromine (Br), or cyano (CN) substituents at the thiophene positions have been synthesized and investigated with regard to their molecular and semiconducting properties. Intense absorption, strong fluorescence, and reversible oxidation and reduction processes are common to all of these dyes. Their characterization as organic semiconductors in vacuum-processed thin-film transistors reveals p-channel operation with field-effect mobilities ranging from 0.01 to 0.7 cm2 V−1 s−1. The highest mobility is found for the DPP dyes bearing the 2-ethylhexyl substituents, which is surprising, considering that as a result of the chiral substituents, this material is a mixture of (R,R), (S,S), and (R,S) stereoisomers. The high carrier mobility in the films of the DPPs bearing stereoisomerically inhomogeneous ethylhexyl groups is rationalized here by single-crystal X-ray diffraction (XRD) analysis in combination with XRD and atomic force microscopy studies on thin films, which reveal the presence of slightly different 2D layer arrangements for the n-alkyl and the 2-ethylhexyl derivatives. For the cyano-substituted DPPs possessing the lowest LUMO levels, ambipolar transport characteristics are observed.

Original languageEnglish (US)
Pages (from-to)7415-7422
Number of pages8
JournalAdvanced Functional Materials
Volume26
Issue number41
DOIs
StatePublished - Nov 2 2016

Keywords

  • charge carrier mobility
  • dyes/pigments
  • organic electronics
  • stereoisomers
  • thin-film transistors

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