Carbonyl (CO)/N-based thermally activated delayed fluorescent materials with high efficiency and fast reverse intersystem crossing rate: a theoretical design and study

Abstract

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) molecular structures can achieve advantages, such as high fluorescence efficiency, reduced structural relaxation and narrow emission. It still remains a challenge to design highly efficient MR structure-based TADF materials with fast reverse intersystem crossing processes and easy emission-color tuning. Herein, we theoretically investigated the recently reported TADF molecule, which has the MR structure of quinolino[3,2,1-de] acridine-5,9-dione (QAD) as the acceptor and the moiety of carbazole (Cz) as the donor, namely QAD-Cz. The calculated fluorescence quantum efficiency of QAD-Cz is as high as 96.5%, which agrees with the experimental results (99.6%) very well. Moreover, we designed two new TADF materials based on the MR-QAD structure with different electron-donating moieties, namely QAD-TPA and QAD-DPTZ. The two newly designed molecules can theoretically achieve high fluorescence quantum efficiencies (over 90%) and fast reverse intersystem crossing rates (e.g. as high as 10⁷ s⁻¹ for QAD-DPTZ). The calculated emission wavelength of the QAD-DPTZ molecule is 638 nm, which obviously widens the emission color range of the reported MR-QAD-based TADF materials. Furthermore, we have analyzed the aggregation effects of the QAD-DPTZ molecule and demonstrated that this novel compound can likewise exhibit excellent luminescence performance in amorphous states.