Synthesis and electroluminescent properties of fluorene-based copolymers containing electron-withdrawing thiazole derivatives

In Hwan Jung, Young Kwan Jung, Jonghee Lee, Jong Hwa Park, Han Young Woo, Jeong Ik Lee, Hye Yong Chu, Hong Ku Shim

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

We synthesized two fluorene-based copolymers poly[(2,5-bis(4-hexylthiophen- 2-yl)thiazolo[5,4-day]thiazole-5,5′-diyl)-alt-(9,9′-dioctylfluorene- 2,7-diyl)] (PFTTZT), and poly[(5,5′-bis(4-hexylthiophen-2-yl)-2,2′- bithiazole-5,5′-diyl)-alt-(9,9′-dioctylfluorene-2,7-diyl)] (PF-TBTT), which contain the electron-withdrawing moieties, thiazolothiazole, and bithiazole, respectively. Through electrochemical studies, we found that these two polymers exhibit stable reversible oxidation and reduction behaviors. Moreover, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PF-TBTT are lower than those of PF-TTZT, and the bandgap of PF-TBTT is smaller than that of PF-TTZT. Thus the bithiazole moiety in PF-TBTT is more electron-withdrawing than the thiazolothiazole moiety in PF-TTZT. Light-emitting devices with indium tin oxide (ITO)/poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)(PEDOT)/polymer/ bis(2-methyl-8-quinolinato)-4-phenylphenolate aluminum (BAlq)/LiF/Al configurations were fabricated. The performance of the PF-TBTT device was found to be almost three times better than that of the PF-TTZT device, which is because electron injection from the cathode to PF-TBTT is much easier than for PF-TTZT. We also investigated the planarity and frontier orbitals of the electron donor-acceptor (D-A) moieties with computational calculations using ab initio Hartree-Fock with the split-valence 6-31G* basis set. These calculations show that TBTT has a more nonplanar structure than TTZT and that the bithiazole moiety is more electron-withdrawing than thiazolothiazole. These calculations are in good agreement with the experimental results.

Original languageEnglish
Pages (from-to)7148-7161
Number of pages14
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Volume46
Issue number21
DOIs
Publication statusPublished - 2008 Nov 1

Keywords

  • Conjugated polymers
  • Copolymerization
  • Electron-withdrawing
  • Light-emitting diodes (LED)

ASJC Scopus subject areas

  • Polymers and Plastics
  • Organic Chemistry
  • Materials Chemistry

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