The effect of heavy atoms replacement sites on the luminescent ways of D-A-D type diphenyl sulfone molecules: Thermally activated delayed fluorescence and phosphorescence

Abstract

To obtain efficient pure organic thermally activated delayed fluorescence (TADF) materials, introducing non-metal heavy atoms is the common molecular design strategy, enhancing the intrinsically weak spin–orbit coupling (SOC) between singlet and triplet excited states by heavy-atom effect. However, the effect of heavy atom replacement sites is rarely explored. Herein, two series of molecules are investigated on the basis of different heavy atoms replacement sites to reveal the inherent structure–property relationships. The results show that DMSeC-DPS, which O is replaced with Se in periphery of donor units, could exhibit enhanced TADF performance. Because (i) sufficiently small singlet–triplet states energy gap (ΔEST) and enhanced SOC as well as mixed CT/LE character in T1 state could facilitate reverse intersystem crossing process, and (ii) non-radiative consumption are decreased for S1→S0 transition. Additionally, replacement of As at the connection site between donor and acceptor units folds evidently the geometry, leading to much larger ΔEST and enhanced exponentially SOC between T1 and S0 state due to the great participation of heavy atoms of the frontier molecules orbitals and heavy-atom effect. The pure LE character leads to relative stability and slight non-radiative consumption in T1 state. The luminescent way of DMOC-As-DPS would be transformed to phosphorescence. This work provides updated theoretical perspective for the effect of heavy atoms replacement sites and proposes a design strategy for the utilization of non-metal heavy atoms in efficiency organic lighting emitting diodes.