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Planar and Rigid Pyrazine Based TADF Emitter for Deep Blue Bright Organic Light Emitting Diodes

preprint
submitted on 22.01.2021, 20:48 and posted on 25.01.2021, 12:34 by P Rajamalli, Dongyang Chen, Subeesh Madayanad Suresh, Youichi Tsuchiya, Chihaya Adachi, Eli Zysman-Colman

Two blue thermally activated delayed fluorescence (TADF) emitters bearing di-tert-butyl carbazoles as the electron donor groups and pyrazine (DTCz-Pz) or dipyrazine (DTCz-Pz) as the electron acceptor are presented. The DFT calculations predict DTCz-Pz and DTCz-DPz to possess high S1 energies (3.19 eV and 3.08 eV, respectively), and relatively large EST values (0.52 eV and 0.56 eV, respectively). The closely layered intermediate triplet states between S1 and T1, predicted by DFT calculations, are expected to facilitate the reverse intersystem crossing (RISC) and improve spin-vibronic coupling efficiency between the excited states even the relatively larger ΔESTs. The ΔESTs for DTCz-Pz and DTCz-DPz are 0.27 eV and 0.38 eV, and both molecules show high photoluminescence quantum yields (65%, and 70%, respectively) and the decay lifetimes show temperature dependence in a PPT host, which is consistent that both molecules are TADF emitters in PPT. The OLEDs based on DTCz-Pz exhibit deep blue emission with λEL of 460 nm and CIE of (0.15, 0.16). The maximum external quantum efficiency (EQEmax) reaches 11.6%, with a maximum luminance (Lmax) of up to 6892 cd m-2, while the device based on DTCz-DPz exhibits sky blue emission with λEL of 484 nm and CIE of (0.15, 0.30), an EQEmax of 7.2%, and Lmax of 8802 cd m-2.

Funding

TADF Emitters for OLEDs

Engineering and Physical Sciences Research Council

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ESPRC-JSPS Core-to-Core Grant Application

Engineering and Physical Sciences Research Council

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Dendron and Dendrimer Derived Thermally Activated Delayed Fluorescence Emitters for Solution-Processed Non-Doped Device

European Commission

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Development of Narrow Band Blue and Red Emitting Macromolecules for Solution-Processed Solid State Lighting Devices

European Commission

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201603780001

History

Email Address of Submitting Author

eli.zysman-colman@st-andrews.ac.uk

Institution

University of St Andrews

Country

United Kingdom

ORCID For Submitting Author

0000-0001-7183-6022

Declaration of Conflict of Interest

No conflict of interest