Journal
CHINESE JOURNAL OF CHEMISTRY
Volume 35, Issue 10, Pages 1559-1568Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cjoc.201700211
Keywords
D-pi-A; organic light emitting diode; exciton utilization; hybridized local and charge-transfer; reverse intersystem crossing
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Funding
- National Natural Science Foundation of China [21334002, 51521002, 51403063]
- Ministry of Science and Technology of China [2013CB834705, 2015CB655003]
- Fundamental Research Funds for the Central Universities [2015ZP001, 2015ZM042]
- Introduced Innovative R&D Team of Guangdong [201101C0105067115]
- Major Science and Technology Project of Guangdong Province [2015B090913002]
- Foundation of Guangzhou Science and Technology Project [201504010012]
- China Post-doctoral Science Fund [2014M562174]
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The donor-pi-conjugated-acceptor (D-pi-A) structure is an important design for the luminescent materials because of its diversity in the selections of donor, pi-bridge and acceptor groups. Herein, we demonstrate two examples of D-pi-A structures capable to finely modulate the excited state properties and arrangement of energy levels, TPA-AN-BP and CZP-AN-BP, which possess the same acceptor and -bridge but different donor. The investigation of their photophysical properties and DFT calculation revealed that the D-pi-A structure with proper donor, pi-bridge and acceptor can result in separation of frontier molecular orbitals on the corresponding donor and acceptor with an obvious overlap on the pi-bridge, resulting in a hybridized local and charge-transfer (HLCT) excited state with high photoluminescent (PL) efficiencies. Meanwhile, their singlet and triplet states are arranged on corresponding moieties with large energy gap between T-2 and T-1, and a small energy gap between S-1 and T-2, which favor the reverse intersystem crossing (RISC) from high-lying triplet levels to singlet levels. As a result, the sky-blue emission non-doped OLED based on the TPA-AN-BP reached maximum external quantum efficiency (EQE) of 4.39% and a high exciton utilization efficiency (EUE) of 77%. This study demonstrates a new strategy to construct highly efficient OLED materials.
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