Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties
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GRAPHICAL ABSTRACT
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PUBLIC SUMMARY
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Bipolar near-ultraviolet emitters with [2.2]paracyclophane linker show circularly polarized emission.
[2.2]Paracyclophane linker restrains charge transfer between electron-donor and acceptor in near-ultraviolet emitters.
Highly efficient circularly polarized OLEDs emit near-ultraviolet electroluminescence.
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ABSTRACT
As linking unit, [2.2]paracyclophane (PCP) has been inserted in between electron-donating groups (i.e. carbazole and 10H-phenoxazine) and electron-accepting groups (i.e. triphenyl-1,3,5-triazine and diphenylsulfone) to prepare a series of linear bipolar racemic near-ultraviolet (NUV) emitters owing to the planar chirality associated with the PCP. In toluene, the racemic bipolar PCP-based emitters can show emission wavelength in the range of 400-444 nm. Critically, very small Commission Internationale de L’Eclairage (CIE) chromaticity coordinate of y value of 0.03 has been achieved for the photoluminescent spectra of these bipolar racemic NUV emitters in solution. The PCP-based bipolar emitters can show efficient NUV emission with photoluminescent quantum yields (PLQY) of ca. 0.5 in doped mCP film. In addition, the enantiomers of the NUV emitters have been obtained to show obvious circular dichroism (CD) behavior and circularly polarized luminescence (CPL). The absorption asymmetric factor (gabs) of ca. 4.4×10-4 and photoluminescent asymmetric factor (gPL) of ca. 1.5×10-3 can be achieved by the PCP-based NUV enantiomers. After doped in the emission layer of organic light-emitting diodes (OLEDs), efficient NUV and deep blue-emitting OLEDs have been constructed. The NUV OLEDs based on the racemic emitters can achieve forward-viewing maximum external quantum efficiency (ηext) of 5.03% and electroluminescence (EL) peak at 404 nm with CIEy of 0.05, while the OLEDs with deep blue emission can show ηext of 4.12% and EL peak at 412 nm with CIEy of 0.08. Furthermore, the NUV chiral enantiomers can bring ηext of 5.25% and EL peak at 404 nm with CIEy of 0.05, while the deep blue chiral enantiomers can give ηext of 4.40% and EL peak at 412 nm with CIEy of 0.08. Clearly, these encouraging EL data show the great potential of these linear PCP-based bipolar emitters in the field of OLEDs. -
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REFERENCES
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Sun Y., Wang H., Liu S., et al., (2023). Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties. The Innovation Materials 1(2), 100028. https://doi.org/10.59717/j.xinn-mater.2023.100028
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Sun Y., Wang H., Liu S., et al., (2023). Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties. The Innovation Materials 1(2), 100028. https://doi.org/10.59717/j.xinn-mater.2023.100028
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Figure 1.
Synthesis of the PCP-based racemic emitters.
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Figure 2.
Absorption behavior and the corresponding key front molecular orbitals
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Figure 3.
PL spectra in different medium and the natural transion orbitals
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Figure 4.
CD spectra for the enantiomers of rac-TzDN(A) and rac -PsDN (B) and CPL spectra for the enantiomers of rac -TzDN (C) and rac -PsDN(D).
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Figure 5.
EL spectra for the optimized OLEDs based on the PCP-based emitters with bipolar feature at ca. 8 V.
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Figure 6.
Circularly polarized electroluminescence (CPEL) spectra at ca. 10 V.
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Figure 7.
Current density-voltage-luminance (J-V-L) characteristics for the OLEDs based on the chiral enantiomers.
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Figure 8.
Relationship between EL efficiencies and luminance for the the OLEDs based on the chiral enantiomers.
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