(Invited) Quantitative Prediction of Exciton Dynamics
Authors: Kaji Hironori 
Published: August 2024

Thermally activated delayed fluorescence (TADF) is now an established way to convert inhelently dark triplet excitons into light through reverse intersystem crossing (RISC).1-4 To realize the RISC process, minimizing the energy gap (ΔE
ST) between S1 and T1 is considered to be effective theoretically, and this has been realized experimentally. At the beginning of the research, RISC had been the rate-limiting process in TADF, although RISC was possible. In such situation, we have shown that acceleration of RISC has now become possible through a variety of methods.5-7

Although excellent TADF materials and highly efficient TADF-based organic light-emitting diodes (OLEDs) have been realized as described above, the fundamental understanding is still insufficient. In the presentation, we first show our recently-proposed method for quantitatively predicting rate constants of all electronic transitions relevant to light emission.8-10 The method proposed here has successfully predicted all rate constants quantitatively and therefore can predict TADF performance precisely. The method also allows quantitative predictions of dynamics (time evolution) of experimentally-obtained rate constants for radiative, non-radiative, intersystem crossing, and RISC as well as exciton population dynamics.11 Such an approach will contribute significantly to the fundamental science of exciton dynamics.
We express sincere thanks to my group members. This work was supported by JSPS KAKENHI Grant Numbers JP20H05840 (Grant-in-Aid for Transformative Research Areas, “Dynamic Exciton”). Computation time and NMR measurements were supported by the international Joint Usage/Research Centre at the Institute for Chemical Research, Kyoto University, Japan.

Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C., Highly efficient organic light-emitting diodes from delayed fluorescence. Nature
2012, 492, 234.

Kaji, H., et al., Purely organic electroluminescent material realizing 100% conversion from electricity to light. Nat. Commun.
2015, 6, 8476.

Yang, Z., et al., Recent advances in organic thermally activated delayed fluorescence materials. Chem. Soc. Rev.
2017, 46, 915.

Wong, M. Y.; Zysman-Colman, E., Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Adv. Mater.
2017, 29, 1605444.

Wada, Y.; Nakagawa, H.; Matsumoto, S.; Wakisaka, Y.; Kaji, H., Organic light emitters exhibiting very fast reverse intersystem crossing. Nat. Photon.
2020, 14, 643.

Ren, Y.; Wada, Y.; Suzuki, K.; Kusakabe, Y.; Geldsetzer, J.; Kaji, H., Efficient blue thermally activated delayed fluorescence emitters showingvery fast reverse intersystem crossing. Appl. Phys. Express
2021, 14, 071003.

Wada, Y.; Wakisaka, Y.; Kaji, H., Efficient direct reverse intersystem crossing between charge transfer‐type singlet and triplet states in a purely organic molecule. ChemPhysChem
2021, 22, 625.

Shizu, K.; Kaji, H., Theoretical determination of rate constants from excited states: Application to benzophenone. J. Phys. Chem. A
2021, 125, 9000.

Shizu, K.; Kaji, H., Comprehensive understanding of multiple resonance thermally activated delayed fluorescence through quantum chemistry calculations. Commun. Chem.
2022, 5.

Shizu, K.; Ren, Y. X.; Kaji, H., Promoting reverse intersystem crossing in thermally activated delayed fluorescence via the heavy-atom effect. J. Phys. Chem. A
2023, 127, 439.

Shizu, K.; Kaji, H., submitted.