Rational Molecular Design for Balanced Locally Excited and Charge- Transfer Nature for Two-Photon Absorption Phenomenon and Highly Efficient TADF-Based OLEDs

Gomathi Vinayakam Mageswari; Youhei Chitose; Youichi Tsuchiya; Ja-Hon Lin; Chihaya Adachi

doi:10.1002/anie.202420417

Rational Molecular Design for Balanced Locally Excited and Charge- Transfer Nature for Two-Photon Absorption Phenomenon and Highly Efficient TADF-Based OLEDs

Angew Chem Int Ed Engl. 2024 Nov 25:e202420417. doi: 10.1002/anie.202420417. Online ahead of print.

Authors

Gomathi Vinayakam Mageswari¹, Youhei Chitose^{1

2}, Youichi Tsuchiya¹, Ja-Hon Lin³, Chihaya Adachi^{1

4}

Affiliations

¹ Center for Organic Photonics and Electronics Research (OPERA) and Department of Applied Chemistry, Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.
² Department of Applied Chemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, Fukuoka, 819-0395, Japan.
³ Department of Electro-Optical Engineering, Advanced Nanophotonics Technology Laboratory, National Taipei University of Technology, Taipei, 10608, Taiwan.
⁴ International Institute for Carbon Neutral Energy Research (I2CNER), Kyushu University, 744 Motooka, Nishi, Fukuoka, 819-0395, Japan.

PMID: 39587453
DOI: 10.1002/anie.202420417

Abstract

The pursuit of highly efficient thermally activated delayed fluorescence (TADF) emitters with two-photon absorption (2PA) character is hampered by the concurrent achievement of a small singlet-triplet energy gap (ΔE_ST) and high photoluminescence quantum yield (Φ_PL). Here, by introducing a terephthalonitrile unit into a sterically crowded donor-π-donor structure, inducing a hybrid electronic excitation character, we designed unique TADF emitters possessing 2PA ability. This rational molecular design was achieved through a main π-conjugated donor-acceptor-donor backbone in line with locally excited feature renders a large oscillator strength and transition dipole moment, maintaining a high 2PA cross-section value. The ancillary N-donor-acceptor-donor with charge transfer character highly balances the TADF phenomenon by minimizing ΔE_ST. A near-unity Φ_PL value with a large radiative decay rate over an order of magnitude higher than the intersystem crossing rate and a high horizontal orientation ratio of 0.95 were simultaneously attained for TPCz2NP. The organic light-emitting diodes fabricated with this material exhibit a high maximum external quantum efficiency of 25.4 % with an elevated 2PA cross-section (σ₂) value up to 143 GM at 850 nm. These findings offer a venue for designing high-performance TADF emitters with exceptional performance inclusive of 2PA properties, expanding for future functional material design.

Keywords: Horizontal orientation; Organic light-emitting diodes; Reverse intersystem crossing; Thermally-activated delayed fluorescence; Two-photon absorption.

Abstract

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