Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor
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The carbazolophane (Czp) donor unit (indolo[2.2]paracyclophane) is introduced to the design pool of donors in thermally activated delayed fluorescence emitters. The increased steric bulk of the annelated donor unit forces an increased torsion between the carbazole and the aryl bridge resulting in a decreased ΔEST and an enhancement of the thermally activated delayed fluorescence in the triazine-containing emitter CzpPhTrz. Further, the closely stacked carbazole and benzene units of the paracyclophane show through-space π–π interactions, effectively increasing the spatial occupation for the HOMO orbital. The chiroptical properties of enantiomers of [2.2]paracyclophane reveal mirror image circular dichroism (CD) and circularly polarized luminescence (CPL) with glum of 1.3 × 10-3. rac- CzpPhTrz is a sky-blue emitter with λPL of 480 nm, a very small ΔEST of 0.16 eV and high ΦPL of 70% in 10 wt.% doped DPEPO films. Sky blue-emitting OLEDs were fabricated with this new TADF emitter showing a high maximum EQE of 17% with CIE coordinates of (0.17, 0.25). A moderate EQE roll-off was also observed with an EQE of 12% at a display relevant luminance of 100 cd m-2. Our results show that the Czp donor contributes to both a decreased ΔEST and an increased photoluminescence quantum yield, both advantageous in the molecular design of TADF emitters.
Sharma , N , Spuling , E , Mattern , C , Li , W , Fuhr , O , Tsuchiya , Y , Adachi , C , Bräse , S , Samuel , I D W & Zysman-Colman , E 2019 , ' Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor ' , Chemical Science , vol. 10 , no. 27 , pp. 6689-6696 . https://doi.org/10.1039/C9SC01821B
Copyright © 2019 The Author(s). Open Access Article. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
DescriptionWe are grateful to the EPSRC for financial support (grants EP/ P010482/1, EP/J01771X, and EP/J00916). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. E.Z.-C. thanks the University of St Andrews for support. E. S. and S. B. acknowledge funding from DFG in the frame of SFB1176 (projects A4, B3 and C6) and KSOP (fellowship to E. S.). We are grateful to JST-ERATO for financial support (grant JPMJER1305). We thank the JSPS Core-to-Core Program for financial support. The measurement of CPL was made using CPL-200 (JASCO) at the Natural Science Center for Basic Research and Development (N-BARD), Hiroshima University.
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