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학술지 Synthesis and Electroluminescent Properties of Fluorene-Based Copolymers Containing Electron-Withdrawing Thiazole Derivatives
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정인환, 정영관, 이종희, 박종화, 우한영, 이정익, 추혜용, 심홍구
Journal of Polymer Science Part A : Polymer Chemistry, v.46 no.21, pp.7148-7161
John Wiley & Sons
07IB1600, 고효율 백색 OLED 소자 기술 개발, 추혜용
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. © 2008 Wiley Periodicals, Inc.
KSP 제안 키워드
Ab initio, Basis set, Electrochemical studies, Electroluminescent properties, Electron donor-acceptor, Electron-withdrawing, Frontier orbitals, Hartree-Fock, Highest occupied molecular orbital, Methyl-, Nonplanar structure