Extended theoretical modeling of reverse intersystem crossing for thermally activated delayed fluorescence materials

07 August 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Thermally activated delayed fluorescence (TADF) materials and multi-resonant (MR) variants are promising organic emitters that can achieve an internal electroluminescence quantum efficiency of approximately 100%. The reverse intersystem crossing (RISC) is key for harnessing triplet energies for fluorescence. Theoretical modeling is thus crucial to estimate its rate constant kRISC for material development. Herein, we present a comprehensive assessment of the theory for simulating the RISC of MR-TADF molecules within a perturbative excited-state dynamics framework. Our extended rate formula reveals the importance of the concerted effects of nonadiabatic spin-vibronic coupling and vibrationally induced spin-orbital couplings in reliably determining kRISC of MR-TADF molecules. The excited singlet-triplet energy gap is another factor influencing kRISC. We present a new scheme for gap estimation using experimental Arrhenius plots of kRISC. Erroneous behavior caused by approximations in Marcus theory is elucidated by testing 121 MR-TADF molecules. Our extended modeling offers in-depth descriptions of kRISC.

Keywords

Multi‐Resonance Thermally Activated Delayed Fluorescence
Reverse Intersystem Crossing
Thermal Vibration Correlation Function Theory
Spin Vibronic Coupling

Supplementary materials

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