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Dual-emissive 2-(2'-hydroxyphenyl)oxazoles for high performance organic electroluminescent devices: discovery of a new equilibrium of excited state intramolecular proton transfer with reverse intersystem crossing process

Abstract

The photoluminescence (PL) and electroluminescence (EL) properties of two highly efficient excited state intramolecular proton transfer (ESIPT) molecules, 2-(2'-hydroxyphenyl)oxazoles containing one triphenylamine (TPA) (1) and two TPA (2) respectively, are studied systematically. The enol-forms of both 1 and 2 possess highly hybridized local and charge transfer (HLCT) excited state character, while their excited-state keto-forms are not of obvious HLCT character. The 1-based device exhibits green-white electroluminescence with Commission Internationale d'Eclairage (CIE) coordinates (0.25, 0.41) and high external quantum efficiency (EQE) up to 5.3%, which is the highest EQE value recorded for single molecular white light-emitting materials. The 2-based device shows sky-blue emission with CIE (0.18, 0.16) and EQE of 8.0%, which is the highest EQE in the reported HLCT materials. The fluorescence intensities of enol-forms of 1 and 2 in EL spectra are increased remarkably relative to their PL spectra. Experimental data and theoretical calculations reveal a new ESIPT equilibrium with a reverse intersystem crossing (RISC) process arising from the HLCT character. In EL, the RISC of the enol-form excitons from the triplet state to the singlet state triggers an increase in enol-form singlet excitons, which further leads to the shift of the ESIPT equilibrium towards an enhanced enol-form emission. Thus, the difference between ESIPT equilibria in PL and EL may be ascribed to the HLCT character of the enol-form excited state.

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Publication details

The article was received on 16 Oct 2017, accepted on 30 Nov 2017 and first published on 01 Dec 2017


Article type: Edge Article
DOI: 10.1039/C7SC04464J
Citation: Chem. Sci., 2017, Accepted Manuscript
  • Open access: Creative Commons BY license
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    Dual-emissive 2-(2'-hydroxyphenyl)oxazoles for high performance organic electroluminescent devices: discovery of a new equilibrium of excited state intramolecular proton transfer with reverse intersystem crossing process

    B. Li, L. Zhou, H. Cheng, Q. Huang, J. Lan, L. Zhou and J. You, Chem. Sci., 2017, Accepted Manuscript , DOI: 10.1039/C7SC04464J

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