Enhancing Reverse Intersystem Crossing in TSCT-TADF Emitters: Heavy Atom Modulation of Multiresonance Acceptors
Jikai Yu, Jia Tang, Zhiying Ma, Hua Wang
Abstract
With the rapid development of thermally activated delayed fluorescence (TADF) materials, achieving efficient reverse intersystem crossing (RISC) to mitigate triplet–triplet annihilation has emerged as a prominent research focus. This study investigates five derivative molecules, featuring varied bridging atoms/groups (O, S, Se, −CH 2 −), designed from the reported TADF molecule AC-BO with through-space charge transfer (TSCT) properties. Utilizing time-dependent density functional theory coupled with a PCM solution model, their excited state behaviors were simulated in a toluene environment. Interestingly, it was observed that RISC in AC-BO and one derivative, AC-BCO, occurs predominantly via the T 2 state rather than the typical T 1 state ( 3 LE B, where B denotes the fluorene bridge), distinguishing it from conventional TSCT-TADF compounds, where RISC typically involves transitions between the 3 CT and 1 CT states. This distinctive mode is attributed to reduced spin–orbit coupling (SOC) between 1 CT and 3 LE B, with T 2 representing a significant contributor to the RISC process through its 3 CT character. Introduction of heavy atoms enhances the electron-withdrawing ability of the acceptor unit, leading to the T 1 transitions exhibiting 3 MRCT characteristics and increased SOC, thereby favoring RISC via 3 MRCT to 1 CT transitions. This study not only deepens our understanding of transition mechanisms in TSCT-TADF compounds but also provides crucial insights into the molecular design and regulation of excited triplet states.