[15p-E402-1~18] 12.4 Organic light-emitting devices and organic transistors

[15p-E402-12] Accelerating Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence via Heavy-Atom Effect

〇Katsuyuki Shizu¹, Yongxia Ren¹, Hironori Kaji¹ (1.Kyoto Univ.)

Keywords:reverse intersystem crossing, heavy-atom effect, delayed fluorescence

Thermally activated delayed fluorescence (TADF) molecules are promising for developing durable organic light-emitting diodes. Increasing the rate constant for reverse intersystem crossing (RISC) is a practical approach to improving the device lifetime. In this study, we present a theoretical method of reproducing all the relevant rate constants of a sulfur-containing TADF molecule (k_RISC ~ 10⁸ s⁻¹.) as an example. We reveal how the heavy atom promotes the RISC process. Aiming at further increasing k_RISC, we theoretically investigate selenium-, tellurium-, and polonium-containing TADF molecules. Our calculations predict that the selenium- and tellurium-containing molecules will show k_RISC >10¹⁰ s⁻¹. Meanwhile, the polonium-containing molecule will show phosphorescence without exhibiting TADF. These findings indicate that too strong heavy-atom effect is unfavorable for simultaneously realizing rapid RISC and efficient TADF.