Research ArticleMATERIALS SCIENCE

Excited state engineering for efficient reverse intersystem crossing

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Science Advances  22 Jun 2018:
Vol. 4, no. 6, eaao6910
DOI: 10.1126/sciadv.aao6910
  • Fig. 1 Excited state energy level alignment for RISC.

    (A) Chemical structure of 5CzBN. (B) Schematic illustration of 1CT1, 3CT1, and 3LE1 energy level alignment for RISC. (C) Chemical structure of D-D2-A–type CzBN derivatives. The second type of substituted donor units is highlighted in the chemical structures.

  • Fig. 2 Photoluminescence properties of D-D2-A–type molecules.

    (A) Steady-state fluorescence spectrum for each molecule in toluene at 295 K. a.u., arbitrary units. (B) PL transient decay curves of CzBN derivatives in oxygen-free toluene at 295 K. (C) Phosphorescence spectra of CzPh, 5CzPh, 2DMeCzPh, 1DPhCzPh, 2DPhCzPh, and 3DPhCzPh in oxygen-free toluene at 77 K. (D) Energy level diagram of CzBN derivatives. The dashed red lines indicate the 3LE1 of CzPh for reference.

  • Fig. 3 Device performance of OLEDs.

    (A) EL spectrum in the OLEDs at 100 cd m−2. (B) EQE in the OLEDs as a function of luminance. Inset: Normalized EQE characteristics in the OLEDs. (C) Normalized luminance of the OLEDs as a function of operating time at a constant current density. The initial luminance was 1000 cd m−2 for each OLED, corresponding to constant driving current density at 2.4 and 1.6 mA cm−2 for 5CzBN- and 3Cz2DPhCzBN-based OLEDs, respectively. (D) Current density–voltage characteristics for OLEDs (filled circles), EODs (open squares), and HODs (open circles) based on 5CzBN or 3Cz2DPhCzBN as dopant.

  • Table 1 Photophysical characteristics of CzBN derivatives in toluene
    CompoundPLmax
    (nm)
    PLQY
    (%)*
    ΔEST
    (eV)
    Embedded Image
    (eV)
    Embedded Image
    (eV)§
    Ea (eV)τp (ns)τd (μs)kr
    (107 s−1)
    kISC
    (108 s−1)
    kRISC
    (105 s−1)
    knrT
    (104 s−1)
    5CzBN4707/750.170.32−0.100.133.846.81.92.52.20.6
    3Cz2DMeCzBN4808/850.170.30−0.130.105.923.61.31.54.40.7
    4Cz1DPhCzBN48011/850.150.16−0.010.097.019.41.61.33.90.9
    3Cz2DPhCzBN4809/810.150.16−0.010.065.812.21.51.57.21.7
    2Cz3DPhCzBN49213/830.130.19−0.060.085.26.12.51.710.23.2

    *PLQY for before (left) and after (right) Ar bubbling. The error is ±2%.

    †Energy gap between S1 and T1 states. The error is ±0.03 eV.

    ‡Energy gap between 3CT1 and 3LE1 states. The error is ±0.03 eV.

    §Energy gap between 1CT1 and 3LE1 states. The error is ±0.03 eV.

    ¶The error is ±0.01 eV.

    • Table 2 Photophysical characteristics of 20 wt %–doped mCBP films
      CompoundPLmax (nm)PLQY (%)*τp (ns)τd (μs)kr (107 s−1)kISC (108 s−1)kRISC (105 s−1)knrT (104 s−1)
      5CzBN48616/653.210.25.02.63.64.1
      3Cz2DPhCzBN49514/804.55.653.01.99.94.1

      *PLQY for prompt (left) and delayed (right) component. The error is ±2%.

      • Table 3 Device performance of OLEDs based on CzBN emitters
        EmitterVoltage
        (V)*
        EQE
        (%)*
        Current
        efficiency
        (cd A−1)*
        CIE
        (chromaticity
        coordinates)
        LT97
        (hours)
        5CzBN5.0/5.6/
        7.7
        18.0/
        17.0/13.9
        44.9/
        43.6/35.0
        (0.19, 0.41)3
        3Cz2DPhCzBN5.2/5.8/
        7.4
        20.9/20.8/
        18.6
        63.0/
        62.2/55.9
        (0.21, 0.44)110

        *Voltage, EQE, and current efficiency were obtained at 500, 1000, and 5000 cd m−2, respectively. The error for EQE is ±0.2%, which was obtained from at least four devices.

        †Initial luminance of 1000 cd m−2.

        Supplementary Materials

        • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaao6910/DC1

          Synthesis and characterization of CzBN derivatives, 5CzPh, 2DPhCzPh, 2DMeCzPh, and 3DPhCzPh.

          fig. S1. Fluorescence and phosphorescence spectra of the CzBN derivatives.

          fig. S2. Phosphorescence spectra of 5CzBN in toluene and acetonitrile solutions.

          fig. S3. Arrhenius plots of the kRISC for CzBN derivatives.

          fig. S4. Phosphorescence spectra of triphenylamine and 1,4-bis(diphenylamino)benzene in toluene solutions.

          fig. S5. Chemical structure and energy diagram of TADF-OLED devices.

          fig. S6. EQE as a function of luminance for 5CzBN, 3Cz2DMeCzBN, and 3Cz2DPhCzBN.

          fig. S7. EQE–current density in the OLEDs with 5CzBN as emitter.

          fig. S8. 1H and 13C nuclear magnetic resonance (NMR) spectra of 3Cz2DPhCzBN.

          fig. S9. 1H and 13C NMR spectra of 3Cz2DMeCzBN.

          fig. S10. 1H and 13C NMR spectra of 4Cz1DPhCzBN.

          fig. S11. 1H and 13C NMR spectra of 2F3DPhCzBN.

          fig. S12. 1H and 13C NMR spectra of 2Cz3DPhCzBN.

          fig. S13. 1H and 13C NMR spectra of 5CzPh.

          fig. S14. 1H and 13C NMR spectra of 2DPhCzPh.

          fig. S15. 1H and 13C NMR spectra of 3DMeCzPh.

          fig. S16. 1H and 13C NMR spectra of 3DPhCzPh.

        • Supplementary Materials

          This PDF file includes:

          • Synthesis and characterization of CzBN derivatives, 5CzPh, 2DPhCzPh, 2DMeCzPh, and 3DPhCzPh.
          • fig. S1. Fluorescence and phosphorescence spectra of the CzBN derivatives.
          • fig. S2. Phosphorescence spectra of 5CzBN in toluene and acetonitrile solutions.
          • fig. S3. Arrhenius plots of the kRISC for CzBN derivatives.
          • fig. S4. Phosphorescence spectra of triphenylamine and 1,4-bis(diphenylamino)benzene in toluene solutions.
          • fig. S5. Chemical structure and energy diagram of TADF-OLED devices.
          • fig. S6. EQE as a function of luminance for 5CzBN, 3Cz2DMeCzBN, and 3Cz2DPhCzBN.
          • fig. S7. EQE–current density in the OLEDs with 5CzBN as emitter.
          • fig. S8. 1H and 13C nuclear magnetic resonance (NMR) spectra of 3Cz2DPhCzBN.
          • fig. S9. 1H and 13C NMR spectra of 3Cz2DMeCzBN.
          • fig. S10. 1H and 13C NMR spectra of 4Cz1DPhCzBN.
          • fig. S11. 1H and 13C NMR spectra of 2F3DPhCzBN.
          • fig. S12. 1H and 13C NMR spectra of 2Cz3DPhCzBN.
          • fig. S13. 1H and 13C NMR spectra of 5CzPh.
          • fig. S14. 1H and 13C NMR spectra of 2DPhCzPh.
          • fig. S15. 1H and 13C NMR spectra of 3DMeCzPh.
          • fig. S16. 1H and 13C NMR spectra of 3DPhCzPh.

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