4.8 Article

TADF Invariant of Host Polarity and Ultralong Fluorescence Lifetimes in a Donor-Acceptor Emitter Featuring a Hybrid Sulfone-Triarylboron Acceptor

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Publisher

WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202217530

Keywords

Acceptor; Emitter; Organic Light-Emitting Diodes; Thermally Activated Delayed Fluorescence; Vibronic Coupling

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The high triplet boracycle SO2B was successfully applied in TADF emitters PXZ-Dipp-SO2B and CZ-Dipp-SO2B, achieving near-complete separation of highest occupied and lowest unoccupied molecular orbitals and leading to low oscillator strength of the S-1 -> S-0 CT transition. OLEDs using CZ-Dipp-SO2B as the luminescent dopant displayed high external quantum efficiency and maximum luminance with low efficiency roll off. The rISC in CZ-Dipp-SO2B is mediated through vibronic coupling of two CT states, allowing stable OLED performance to be achieved in different host environments.
10H-Dibenzo[b,e][1,4]thiaborinine 5,5-dioxide (SO2B)-a high triplet (T-1=3.05 eV) strongly electron-accepting boracycle was successfully utilised in thermally activated delayed fluorescence (TADF) emitters PXZ-Dipp-SO2B and CZ-Dipp-SO2B. We demonstrate the near-complete separation of highest occupied and lowest unoccupied molecular orbitals leading to a low oscillator strength of the S-1 -> S-0 CT transition, resulting in very long ca. 83 ns and 400 ns prompt fluorescence lifetimes for CZ-Dipp-SO2B and PXZ-Dipp-SO2B, respectively, but retaining near unity photoluminescence quantum yield. OLEDs using CZ-Dipp-SO2B as the luminescent dopant display high external quantum efficiency (EQE) of 23.3 % and maximum luminance of 18600 cd m(-2) with low efficiency roll off at high brightness. For CZ-Dipp-SO2B, reverse intersystem crossing (rISC) is mediated through the vibronic coupling of two charge transfer (CT) states, without involving the triplet local excited state ((LE)-L-3), resulting in remarkable rISC rate invariance to environmental polarity and polarisability whilst giving high organic light-emitting diode (OLED) efficiency. This new form of rISC allows stable OLED performance to be achieved in different host environments.

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