It matters where the heavy atom is placed: optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance

Dongyang Chen; Hui  Wang; Feng  Huang; David B. Cordes; Aidan P. McKay; Kai  Wang; Xiao-Hong  Zhang; Eli Zysman-Colman

doi:10.1002/adfm.202506189

It matters where the heavy atom is placed: optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance

Dongyang Chen^*, Hui Wang, Feng Huang, David B. Cordes, Aidan P. McKay, Kai Wang^*, Xiao-Hong Zhang^*, Eli Zysman-Colman^*

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

This study explores the impact of the regioisomerism of a heavy chalcogen atom on the photophysical properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. We synthesized two pairs of isomeric MR-TADF emitters containing different benzothienocarbazole moieties, tDPABT1B/tDPABT2B and tCzBT1B/tCzBT2B. Theoretical calculations indicate that
tDPABT2B and tCzBT2B possess higher spin-orbital coupling values (0.27 and 0.60 cm⁻¹) compared to their respective isomers. The photophysical study reveals that tDPABT2B and tCzBT2B have twofold faster reverse intersystem crossing rate constants of 0.5 × 10⁵ and 2.7 × 10⁵ s⁻¹, respectively, than their isomeric counterparts. The sensitizer-free organic light-emitting diodes (OLEDs) with
tCzBT1B and tCzBT2B exhibited green emissions [CIE coordinates of (0.12, 0.54)] and showed high maximum external quantum efficiencies (EQE_max) of 34.9% and 34.3%, respectively. Notably, the device with tCzBT2B demonstrated a reduced efficiency roll-off (34% decrease at 1000 cd cm⁻²) compared to that with tCzBT1B (48% decrease at 1000 cd cm⁻²), highlighting the distinct benefits and importance of the regiochemistry of the heavy atom in contributing to an enhancing device performance.

Original language	English
Article number	2506189
Number of pages	11
Journal	Advanced Functional Materials
Volume	Early View
Early online date	21 Apr 2025
DOIs	https://doi.org/10.1002/adfm.202506189
Publication status	E-pub ahead of print - 21 Apr 2025

Keywords

Heavy atom effect
MR-TADF
OLEDs
RISC
Spin-orbit coupling

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Allan Watson Programme Grant: Boron: Beyond the Reagent
Watson, A. J. B. (PI), Morris, R. E. (CoI), Smith, A. D. (CoI) & Zysman-Colman, E. (CoI)
UK Research and Innovation
1/05/23 → 30/04/28
Project: Standard
Chemistry EPSRC-JSPS: EPSRC-JSPS Core-to-Core Grant Application
Zysman-Colman, E. (PI)
1/08/18 → 31/01/24
Project: Standard

It Matters Where the Heavy Atom is Placed: Optimizing the Spin-Orbital Coupling in Multiresonant TADF (MR-TADF) Emitters and Its Impact on OLED Performance (dataset)
Chen, D. (Creator), Wang, H. (Creator), Huang, F. (Creator), Cordes, D. B. (Creator), McKay, A. (Creator), Wang, K. (Creator), Zhang, X.-H. (Creator) & Zysman-Colman, E. (Creator), University of St Andrews, 30 Apr 2025
DOI: 10.17630/d2dfd394-5fcf-4d4a-ae00-bb771cfc30aa
Dataset

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Chen, D., Wang, H., Huang, F., Cordes, D. B., McKay, A. P., Wang, K., Zhang, X.-H., & Zysman-Colman, E. (2025). It matters where the heavy atom is placed: optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance. Advanced Functional Materials, Early View, Article 2506189. Advance online publication. https://doi.org/10.1002/adfm.202506189

@article{24be0ed1099945fda5863359a7c54baa,

title = "It matters where the heavy atom is placed: optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance",

abstract = "This study explores the impact of the regioisomerism of a heavy chalcogen atom on the photophysical properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. We synthesized two pairs of isomeric MR-TADF emitters containing different benzothienocarbazole moieties, tDPABT1B/tDPABT2B and tCzBT1B/tCzBT2B. Theoretical calculations indicate that tDPABT2B and tCzBT2B possess higher spin-orbital coupling values (0.27 and 0.60 cm⁻¹) compared to their respective isomers. The photophysical study reveals that tDPABT2B and tCzBT2B have twofold faster reverse intersystem crossing rate constants of 0.5 × 10⁵ and 2.7 × 10⁵ s⁻¹, respectively, than their isomeric counterparts. The sensitizer-free organic light-emitting diodes (OLEDs) withtCzBT1B and tCzBT2B exhibited green emissions [CIE coordinates of (0.12, 0.54)] and showed high maximum external quantum efficiencies (EQEmax) of 34.9% and 34.3%, respectively. Notably, the device with tCzBT2B demonstrated a reduced efficiency roll-off (34% decrease at 1000 cd cm⁻²) compared to that with tCzBT1B (48% decrease at 1000 cd cm⁻²), highlighting the distinct benefits and importance of the regiochemistry of the heavy atom in contributing to an enhancing device performance.",

keywords = "Heavy atom effect, MR-TADF, OLEDs, RISC, Spin-orbit coupling",

author = "Dongyang Chen and Hui Wang and Feng Huang and Cordes, {David B.} and McKay, {Aidan P.} and Kai Wang and Xiao-Hong Zhang and Eli Zysman-Colman",

note = "Funding: The study in China was supported by the National Natural Science Foundation of China (Grant Nos. 52130304, 52422309, and 52373193), the National Key Research & Development Program of China (Grant Nos. 2020YFA0714601, 2020YFA0714604), the Science and Technology Program of Suzhou (Grant No. ZXL2022490), Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science & Technology, the 111 Project. D.C. thanks the support from China Postdoctoral Science Foundation (Grant No. 2022TQ0227) and Natural Science Foundation of Jiangsu Province, China (Grant No. BK20230508). In the UK, this project has received funding from the Engineering and Physical Sciences Research Council for support (EP/R035164/1, EP/W007517/1, EP/Z535291/1).",

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month = apr,

day = "21",

doi = "10.1002/adfm.202506189",

language = "English",

volume = "Early View",

journal = "Advanced Functional Materials",

issn = "1616-301X",

publisher = "John Wiley & Sons, Ltd",

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TY - JOUR

T1 - It matters where the heavy atom is placed

T2 - optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance

AU - Chen, Dongyang

AU - Wang, Hui

AU - Huang, Feng

AU - Cordes, David B.

AU - McKay, Aidan P.

AU - Wang, Kai

AU - Zhang, Xiao-Hong

AU - Zysman-Colman, Eli

N1 - Funding: The study in China was supported by the National Natural Science Foundation of China (Grant Nos. 52130304, 52422309, and 52373193), the National Key Research & Development Program of China (Grant Nos. 2020YFA0714601, 2020YFA0714604), the Science and Technology Program of Suzhou (Grant No. ZXL2022490), Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science & Technology, the 111 Project. D.C. thanks the support from China Postdoctoral Science Foundation (Grant No. 2022TQ0227) and Natural Science Foundation of Jiangsu Province, China (Grant No. BK20230508). In the UK, this project has received funding from the Engineering and Physical Sciences Research Council for support (EP/R035164/1, EP/W007517/1, EP/Z535291/1).

PY - 2025/4/21

Y1 - 2025/4/21

N2 - This study explores the impact of the regioisomerism of a heavy chalcogen atom on the photophysical properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. We synthesized two pairs of isomeric MR-TADF emitters containing different benzothienocarbazole moieties, tDPABT1B/tDPABT2B and tCzBT1B/tCzBT2B. Theoretical calculations indicate that tDPABT2B and tCzBT2B possess higher spin-orbital coupling values (0.27 and 0.60 cm⁻¹) compared to their respective isomers. The photophysical study reveals that tDPABT2B and tCzBT2B have twofold faster reverse intersystem crossing rate constants of 0.5 × 10⁵ and 2.7 × 10⁵ s⁻¹, respectively, than their isomeric counterparts. The sensitizer-free organic light-emitting diodes (OLEDs) withtCzBT1B and tCzBT2B exhibited green emissions [CIE coordinates of (0.12, 0.54)] and showed high maximum external quantum efficiencies (EQEmax) of 34.9% and 34.3%, respectively. Notably, the device with tCzBT2B demonstrated a reduced efficiency roll-off (34% decrease at 1000 cd cm⁻²) compared to that with tCzBT1B (48% decrease at 1000 cd cm⁻²), highlighting the distinct benefits and importance of the regiochemistry of the heavy atom in contributing to an enhancing device performance.

AB - This study explores the impact of the regioisomerism of a heavy chalcogen atom on the photophysical properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. We synthesized two pairs of isomeric MR-TADF emitters containing different benzothienocarbazole moieties, tDPABT1B/tDPABT2B and tCzBT1B/tCzBT2B. Theoretical calculations indicate that tDPABT2B and tCzBT2B possess higher spin-orbital coupling values (0.27 and 0.60 cm⁻¹) compared to their respective isomers. The photophysical study reveals that tDPABT2B and tCzBT2B have twofold faster reverse intersystem crossing rate constants of 0.5 × 10⁵ and 2.7 × 10⁵ s⁻¹, respectively, than their isomeric counterparts. The sensitizer-free organic light-emitting diodes (OLEDs) withtCzBT1B and tCzBT2B exhibited green emissions [CIE coordinates of (0.12, 0.54)] and showed high maximum external quantum efficiencies (EQEmax) of 34.9% and 34.3%, respectively. Notably, the device with tCzBT2B demonstrated a reduced efficiency roll-off (34% decrease at 1000 cd cm⁻²) compared to that with tCzBT1B (48% decrease at 1000 cd cm⁻²), highlighting the distinct benefits and importance of the regiochemistry of the heavy atom in contributing to an enhancing device performance.

KW - Heavy atom effect

KW - MR-TADF

KW - OLEDs

KW - RISC

KW - Spin-orbit coupling

U2 - 10.1002/adfm.202506189

DO - 10.1002/adfm.202506189

M3 - Article

SN - 1616-301X

VL - Early View

JO - Advanced Functional Materials

JF - Advanced Functional Materials

M1 - 2506189

ER -

It matters where the heavy atom is placed: optimizing the spin-orbital coupling in multiresonant TADF (MR-TADF) emitters and its impact on OLED performance

Abstract

Keywords

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Projects

Allan Watson Programme Grant: Boron: Beyond the Reagent

Chemistry EPSRC-JSPS: EPSRC-JSPS Core-to-Core Grant Application

Datasets

It Matters Where the Heavy Atom is Placed: Optimizing the Spin-Orbital Coupling in Multiresonant TADF (MR-TADF) Emitters and Its Impact on OLED Performance (dataset)

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