Thermally activated delayed fluorescence (TADF) molecules with dual emission have great potential for use as single emitters in white organic light-emitting diodes (WOLEDs).

Employing dual-emission thermally activated delayed fluorescence (TADF) molecules to fabricate single emitters in highly efficient white organic light-emitting diodes (WOLEDs) is still a challenge. In this work, a systematic study on the luminescence mechanism of three TADF molecules with blue–orange dual emission is performed. It is found that the quasi-axial (ax) conformer is responsible for blue normal fluorescence (NF), while the quasi-equatorial (eq) conformer is responsible for orange TADF. In addition, the upconversion for the TADF molecules happens from the first triplet state (T1) and the second triplet state (T2) to the first singlet state (S1) in the quasi-equatorial conformers. In addition, the transition from T1 to S1 and T2 to S1 also happens in the process of conformation transformation. Besides, our study also indicates that the donor with an asymmetric bond length in the six-membered ring could favor the generation of dual conformations and dual emission. Some molecules with PTZ or PXZ as donors are predicted as potential emitters with white light emission. Our research would favor the design of TADF emitters with dual emission in WOLEDs.

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Thermally activated delayed fluorescence (TADF) molecules have attracted great attention as high efficient luminescent materials. Most of TADF molecules possess small energy gap between the first singlet excited state (S1) and the first triplet excited state (T1) to favor the up-conversion from T1 to S1. In this paper, a new TADF generation mechanism is revealed based on theoretical simulation. By systematic study of the light-emitting properties of SOBF-OMe in both toluene and in aggregation state, we find that the single SOBF-OMe could not realize TADF emission due to large energy gap as well as small up-conversion rates between S1 and T1. Through analysis of dimers, we find that dimers with intermolecular hydrogen bond (H-bond) are responsible for the generation of TADF, since smaller energy gap between S1 and T1 is found and the emission wavelength is in good agreement with experimental counterpart. The emission properties of SOBF-H are also studied for comparison, which reflect the important role of H-bond. Our theoretical results agree ith experimental results well and confirm the mechanism of H-bond induced TADF.

Multifunctional thermally activated delayed fluorescence (TADF) molecules have recently attracted great attention. The light-emitting mechanisms of the TADF molecule PTZ-AQ with aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) in three different aggregation states are studied using the combined quantum mechanics and molecular mechanics (QM/MM) method as well as the thermal vibration correlation function method. It is found that different aggregation patterns would induce different intermolecular interaction and molecular geometries. The different energy diagram of excited states also induce variation of emission colors and (reverse) intersystem crossing processes. By comparing with the light-emitting properties in solvent, the AIE property is confirmed, which is induced by enhanced radiative rate and decreased nonradiative rates in aggregation. The bicolor switch mechanism for the molecule in the solid state should have a close relationship with the dihedral angle change between the donor and the acceptor. The calculation results provide valuable information for understanding the light-emitting mechanism of the PTZ-AQ based polymorphs with AIE and MCL properties, which would favor the design of a new type multifunctional TADF molecules.