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Revealing the Cooperative Relationship Between Spin, Energy, and Polarization Parameters Toward Developing High-Efficiency Exciplex Light-Emitting Diodes

Revealing the Cooperative Relationship Between Spin, Energy, and Polarization Parameters Toward Developing High-Efficiency Exciplex Light-Emitting Diodes

Miaosheng Wang, Yi-Hsuan Huang, Kai-Siang Lin, Tzu-Hung Yeh, Jiashun Duan, Tzu-Yu Ko, Shun-Wei Liu, Ken-Tsung Wong, Bin Hu

Adv Mater. 2019 Nov;31(46):e1904114.

PMID: 31566271

Abstract:

Experimental studies to reveal the cooperative relationship between spin, energy, and polarization through intermolecular charge-transfer dipoles to harvest nonradiative triplets into radiative singlets in exciplex light-emitting diodes are reported. Magneto-photoluminescence studies reveal that the triplet-to-singlet conversion in exciplexes involves an artificially generated spin-orbital coupling (SOC). The photoinduced electron parametric resonance measurements indicate that the intermolecular charge-transfer occurs with forming electric dipoles (D+• →A-• ), providing the ionic polarization to generate SOC in exciplexes. By having different singlet-triplet energy differences (ΔEST ) in 9,9'-diphenyl-9H,9'H-3,3'-bicarbazole (BCzPh):3',3'″,3'″″-(1,3,5-triazine-2,4,6-triyl)tris(([1,1'-biphenyl]-3-carbonitrile)) (CN-T2T) (ΔEST = 30 meV) and BCzPh:bis-4,6-(3,5-di-3-pyridylphenyl)-2-methyl-pyrimidine (B3PYMPM) (ΔEST = 130 meV) exciplexes, the SOC generated by the intermolecular charge-transfer states shows large and small values (reflected by different internal magnetic parameters: 274 vs 17 mT) with high and low external quantum efficiency maximum, EQEmax (21.05% vs 4.89%), respectively. To further explore the cooperative relationship of spin, energy, and polarization parameters, different photoluminescence wavelengths are selected to concurrently change SOC, ΔEST , and polarization while monitoring delayed fluorescence. When the electron clouds become more deformed at a longer emitting wavelength due to reduced dipole (D+• →A-• ) size, enhanced SOC, increased orbital polarization, and decreased ΔEST can simultaneously occur to cooperatively operate the triplet-to-singlet conversion.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP925425963	B3PYMPM		925425-96-3	Price

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