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PreprintCC BYChemRxiv

Efficient Long-Wavelength Through-Space Charge Transfer Thermally Activated Delayed Fluorescence in Conformationally Adaptive Emitters without Conformational Locking

  • Nae Aota1
  • Jaijanarthanan Lingagouder2,3
  • Nuno Gandum4
  • Leonardo Evaristo de Sousa4
  • Lucy A. Weatherill5,6
  • Marc K. Etherington7
  • Norimitsu Tohnai1
  • Satoshi Minakata1
  • Piotr de Silva4
  • Przemyslaw Data2,3,5,6
  • Youhei Takeda1
7 affiliations
  1. 1Department of Applied Chemistry, Graduate School of Engineering, University of Osaka, Yamadaoka 2-1, Suita, Osaka, Japan, 565-0871
  2. 2Faculty of Chemistry
  3. 3Lodz University of Technology
  4. 4Department of Energy Conversion and Storage, Technical University of Denmark, Agnes Nielsens Vej 301, Kongens Lyngby, Denmark, 2800
  5. 5Department of Physics
  6. 6Durham University
  7. 7School of Engineering, Physics and Mathematics, Northumbria University, Ellison Place, Newcastel upon Tyne, United Kingdom, NE18ST
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Abstract

Through-space charge-transfer thermally activated delayed fluorescence (TSCT-TADF) emitters often employ conformationally constrained donor–acceptor architectures to control through-space electronic coupling, particularly for long-wavelength emission. Here, we report conformationally adaptive orange-to-red TSCT-TADF emitters based on an S-shaped donor–π–acceptor–π–donor framework composed of phenoxazine donors, xanthene linkers, and a dibenzo[ a,j ]phenazine acceptor. Structural and NMR analyses reveal substantial conformational mobility, while systematic conformational searches and excited-state calculations identify thermally accessible conformers with distinct donor-acceptor geometries and excited-state characteristics. Comparative studies with reference compounds and fragment-resolved transition-density analysis show that the xanthene linker primarily acts as a conformational regulator and that the low-energy CT states have predominant TSCT character with only minor linker involvement. Temperature-dependent early-time photoluminescence measurements reveal continuous spectral relaxation in fluid toluene that slows upon cooling and is absent in rigid Zeonex and mCBP hosts, providing strong evidence for structural relaxation following photoexcitation within a pre-existing conformational ensemble. The emitters exhibit orange-to-red TADF with reverse intersystem crossing rates on the order of 10 5 –10 6 s −1 . Organic light-emitting diodes employing these emitters show electroluminescence at 598–624 nm, external quantum efficiencies up to 14.9%, and limited efficiency roll-off over a broad luminance range. These results demonstrate that efficient long-wavelength TSCT-TADF can be realized without permanent conformational locking and establish a framework for understanding the interplay between ground-state conformational heterogeneity and excited-state structural relaxation.

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Cite

BibTeXRIS
BibTeX
@misc{aota2026efficient,
  title = {{Efficient Long-Wavelength Through-Space Charge Transfer Thermally Activated Delayed Fluorescence in Conformationally Adaptive Emitters without Conformational Locking}},
  author = {Nae Aota and Jaijanarthanan Lingagouder and Nuno Gandum and Leonardo Evaristo de Sousa and Lucy A. Weatherill and Marc K. Etherington and Norimitsu Tohnai and Satoshi Minakata and Piotr de Silva and Przemyslaw Data and Youhei Takeda},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15004855/v2},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15004855/v2},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Efficient Long-Wavelength Through-Space Charge Transfer Thermally Activated Delayed Fluorescence in Conformationally Adaptive Emitters without Conformational Locking
AU  - Nae Aota
AU  - Jaijanarthanan Lingagouder
AU  - Nuno Gandum
AU  - Leonardo Evaristo de Sousa
AU  - Lucy A. Weatherill
AU  - Marc K. Etherington
AU  - Norimitsu Tohnai
AU  - Satoshi Minakata
AU  - Piotr de Silva
AU  - Przemyslaw Data
AU  - Youhei Takeda
PY  - 2026
DA  - 2026/10/13
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15004855/v2
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15004855/v2
AB  - Through-space charge-transfer thermally activated delayed fluorescence (TSCT-TADF) emitters often employ conformationally constrained donor–acceptor architectures to control through-space electronic coupling, particularly for long-wavelength emission. Here, we report conformationally adaptive orange-to-red TSCT-TADF emitters based on an S-shaped donor–π–acceptor–π–donor framework composed of phenoxazine donors, xanthene linkers, and a dibenzo[ a,j ]phenazine acceptor. Structural and NMR analyses reveal substantial conformational mobility, while systematic conformational searches and excited-state calculations identify thermally accessible conformers with distinct donor-acceptor geometries and excited-state characteristics. Comparative studies with reference compounds and fragment-resolved transition-density analysis show that the xanthene linker primarily acts as a conformational regulator and that the low-energy CT states have predominant TSCT character with only minor linker involvement. Temperature-dependent early-time photoluminescence measurements reveal continuous spectral relaxation in fluid toluene that slows upon cooling and is absent in rigid Zeonex and mCBP hosts, providing strong evidence for structural relaxation following photoexcitation within a pre-existing conformational ensemble. The emitters exhibit orange-to-red TADF with reverse intersystem crossing rates on the order of 10 5 –10 6 s −1 . Organic light-emitting diodes employing these emitters show electroluminescence at 598–624 nm, external quantum efficiencies up to 14.9%, and limited efficiency roll-off over a broad luminance range. These results demonstrate that efficient long-wavelength TSCT-TADF can be realized without permanent conformational locking and establish a framework for understanding the interplay between ground-state conformational heterogeneity and excited-state structural relaxation.
ER  -