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. 2021 Aug 23;60(35):19364-19373.
doi: 10.1002/anie.202106570. Epub 2021 Jul 21.

Tetrabenzo[a,c]phenazine Backbone for Highly Efficient Orange-Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation

Umamahesh Balijapalli  1 , Yi-Ting Lee  1 , Buddhika S B Karunathilaka  1 , Ganbaatar Tumen-Ulzii  1 , Morgan Auffray  1 , Youichi Tsuchiya  1 , Hajime Nakanotani  1   2 , Chihaya Adachi  1   2
Affiliations

Tetrabenzo[a,c]phenazine Backbone for Highly Efficient Orange-Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation

Umamahesh Balijapalli et al. Angew Chem Int Ed Engl. .

Abstract

Three thermally activated delayed fluorescence (TADF) molecules, namely PQ1, PQ2, and PQ3, are composed of electron-accepting (A) tetrabenzo[a,c]phenazine (TBPZ) and electron-donating (D) phenoxazine (PXZ) units are designed and characterized. The combined effects of planar acceptor manipulation and high steric hindrance between D and A units endow high molecular rigidity that suppresses nonradiative decay of the excitons with improved photoluminescence quantum yields (PLQYs). Particularly, the well-aligned excited states involving a singlet and a triplet charge-transfer excited states and a localized excited triplet state in PQ3 enhances the reverse intersystem crossing rate constant (kRISC ) with a short delay lifetime (τd ). The orange-red OLED based on PQ3 displays a maximum external EL quantum efficiency (EQE) of 27.4 % with a well-suppressed EL efficiency roll-off owing to a completely horizontal orientation of the transition dipole moment in the film state.

Keywords: horizontal orientation; organic light-emitting diodes; reverse intersystem crossing; suppressed efficiency roll-off; thermally activated delayed fluorescence.

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