Achieving Intrinsic Luminescence of Pure Organic Mono- and Di-Radicals in Aggregated States

Abstract

Organic luminescent radicals are promising for optoelectronic applications, yet their practical implementation remains hindered by aggregation-caused quenching (ACQ) in aggregated states. In this study, we present a molecular design strategy that enables unprecedented intrinsic luminescence from pure radicals across multiple aggregated states, including crystalline states, powders, and amorphous films, through the incorporation of sterically demanding TPP (2,4,6-triisopropylphenyl) groups. Comprehensive photophysical characterization coupled with structural analysis reveals that the TPP moieties effectively suppress detrimental intermolecular interactions, particularly exchange coupling and π–π stacking between radical centers. The luminescent properties were analyzed via systematic theoretical calculations. The universality of this design principle is further demonstrated through its successful application to diradical systems, including Chichibabin's and Müller's hydrocarbons, which exhibit significantly enhanced emission in aggregated states. This work establishes a generalizable strategy for designing stable and efficient luminescent radicals in aggregated states, opening new avenues for radical-based optoelectronic devices.

Keywords

aggregated states / diradicals / intrisic luminescence / organic luminescent radicals

References

[1] Q. Peng, A. Obolda, M. Zhang, and F. Li, “Organic Light-Emitting Diodes Using a Neutral π Radical as Emitter: The Emission From a Doublet,” Angewandte Chemie 54 (2015): 7197-7201.

[2] X. Ai, E. W. Evans, S. Dong, et al., “Efficient Radical-Based Light-Emitting Diodes With Doublet Emission,” Nature 563 (2018): 536-540.

[3] S. Kimura, T. Kusamoto, S. Kimura, K. Kato, Y. Teki, and H. Nishihara, “Magnetoluminescence in a Photostable, Brightly Luminescent Organic Radical in a Rigid Environment,” Angewandte Chemie 57 (2018): 12711-12715.

[4] R. Matsuoka, S. Kimura, T. Miura, T. Ikoma, and T. Kusamoto, “Single-Molecule Magnetoluminescence From a Spatially Confined Persistent Diradical Emitter,” Journal of the American Chemical Society 145 (2023): 13615-13622.

[5] A. Abdurahman, L. Shen, J. Wang, et al., “A Highly Efficient Open-Shell Singlet Luminescent Diradical With Strong Magnetoluminescence Properties,” Light: Science & Applications 12 (2023): 272.

[6] Y. Zhao, A. Abdurahman, Y. Zhang, P. Zheng, M. Zhang, and F. Li, “Highly Efficient Multifunctional Luminescent Radicals,” CCS Chemistry 4 (2022): 722-731.

[7] J.-W. Yuan, Q.-C. Peng, J.-C. Fu, et al., “Highly Efficient Stable Luminescent Radical-Based X-Ray Scintillator,” Journal of the American Chemical Society 145 (2023): 27095-27102.

[8] A. Luo, J. Zhang, D. Xiao, et al., “Efficient Metal Free Organic Radical Scintillators,” Nature Communications 15 (2024): 8181.

[9] S. Gorgon, K. Lv, J. Grüne, et al., “Reversible Spin-Optical Interface in Luminescent Organic Radicals,” Nature 620 (2023): 538-544.

[10] L. Zhao, H. Liu, W. Li, et al., “Stable Diradical-Derived Conjugated Radical Polymers,” Angewandte Chemie (2025): e202507603, https://doi.org/10.1002/anie.202507603.

[11] Z. Zhou, K. Yang, L. He, et al., “Sulfone-Functionalized Chichibabin's Hydrocarbons: Stable Diradicaloids With Symmetry Breaking Charge Transfer Contributing to NIR Emission Beyond 900 Nm,” Journal of the American Chemical Society 146 (2024): 6763-6772.

[12] L. Feng, Y. Tuo, Z. Wu, et al., “Highly Stable Near-Infrared II Luminescent Diradicaloids for Cancer Phototheranostics,” Journal of the American Chemical Society 146 (2024): 32582-32594.

[13] J. Kida, D. Aoki, and H. Otsuka, “Mechanophore Activation Enhanced by Hydrogen Bonding of Diarylurea Motifs: An Efficient Supramolecular Force-Transducing System,” Aggregate 2 (2021): e50.

[14] J. Huang, Z. Wang, W. Zhu, and Y. Li, “Solution-Processed D-A-π-A-D Radicals for Highly Efficient Photothermal Conversion,” Aggregate 5 (2024): e426.

[15] Y. Zhu, Z. Zhu, S. Wang, Q. Peng, and A. Abdurahman, “Stable Luminescent Diradicals: The Emergence and Potential Applications,” Angewandte Chemie 64 (2025): e202423470.

[16] A. Abdurahman, T. J. H. Hele, Q. Gu, et al., “Understanding the Luminescent Nature of Organic Radicals for Efficient Doublet Emitters and Pure-Red Light-Emitting Diodes,” Nature Materials 19 (2020): 1224-1229.

[17] A. Abdurahman, J. Wang, Y. Zhao, P. Li, L. Shen, and Q. Peng, “A Highly Stable Organic Luminescent Diradical,” Angewandte Chemie 62 (2023): e202300772.

[18] Z. Zhu, Z. Kuang, L. Shen, et al., “Dual Channel Emissions of Kasha and Anti-Kasha from a Single Radical Molecule,” Angewandte Chemie International Edition 63 (2024): e202410552.

[19] Y. Hattori, R. Kitajima, W. Ota, et al., “The Simplest Structure of a Stable Radical Showing High Fluorescence Efficiency in Solution: Benzene Donors With Triarylmethyl Radicals,” Chemical Science 13 (2022): 13418.

[20] M. Ito, S. Shirai, Y. Xie, et al., “Fluorescent Organic π-Radicals Stabilized With Boron: Featuring a SOMO-LUMO Electronic Transition,” Angewandte Chemie International Edition 61 (2022): e202201965.

[21] C. Lu, E. Cho, K. Wan, et al., “Achieving Nearly 100% Photoluminescence Quantum Efficiency in Organic Radical Emitters by Fine-Tuning the Effective Donor-Acceptor Distance,” Advanced Functional Materials 34 (2024): 2314811.

[22] J. Shi, W. Xu, H. Yu, et al., “A Highly Luminescent Metallo-Supramolecular Radical Cage,” Journal of the American Chemical Society 145 (2023): 24081-24088.

[23] X. Li, Y.-L. Wang, C. Chen, Y.-Y. Ren, and Y.-F. Han, “A Platform for Blue-Luminescent Carbon-Centered Radicals,” Nature Communications 13 (2022): 5367.

[24] C. Yan, D. An, W. Chen, et al., “Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)Methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry,” CCS Chemistry 4 (2022): 3190-3203.

[25] A. Obolda, X. Ai, M. Zhang, and F. Li, “Up to 100% Formation Ratio of Doublet Exciton in Deep-Red Organic Light-Emitting Diodes Based on Neutral π-Radical,” ACS Applied Materials & Interfaces 8 (2016): 35472-35478.

[26] C.-H. Liu, E. Hamzehpoor, Y. Sakai-Otsuka, T. Jadhav, and D. F. Perepichka, “A Pure-Red Doublet Emission With 90 % Quantum Yield: Stable, Colorless, Iodinated Triphenylmethane Solid,” Angewandte Chemie 59 (2020): 23030-23034.

[27] A. Abdurahman, Q. Peng, O. Ablikim, X. Ai, and F. Li, “A Radical Polymer With Efficient Deep-Red Luminescence in the Condensed State,” Materials Horizons 6 (2019): 1265-1270.

[28] L. Hou, H. Xu, X. Zhang, et al., “Impact of Polymer Rigidity on the Thermoresponsive Luminescence and Electron Spin Resonance of Polyester-Tethered Single Radicals,” Macromolecules 55 (2022): 8619-8628.

[29] S. Kimura, A. Tanushi, T. Kusamoto, S. Kochi, T. Sato, and H. Nishihara, “A Luminescent Organic Radical With Two Pyridyl Groups: High Photostability and Dual Stimuli-Responsive Properties, With Theoretical Analyses of Photophysical Processes,” Chemical Science 9 (2018): 1996-2007.

[30] S. Kimura, M. Uejima, W. Ota, et al., “An Open-Shell, Luminescent, Two-Dimensional Coordination Polymer With a Honeycomb Lattice and Triangular Organic Radical,” Journal of the American Chemical Society 143 (2021): 4329-4338.

[31] R. Matsuoka, S. Kimura, and T. Kusamoto, “Solid-State Room-Temperature Near-Infrared Photoluminescence of a Stable Organic Radical,” ChemPhotoChem 5 (2021): 669-673.

[32] P. Murto, B. Li, Y. Fu, et al., “Steric Control of Luminescence in Phenyl-Substituted Trityl Radicals,” Journal of the American Chemical Society 146 (2024): 13133-13141.

[33] Y. Mu, Y. Liu, H. Tian, et al., “Sensitive and Repeatable Photoinduced Luminescent Radicals From a Simple Organic Crystal,” Angewandte Chemie 60 (2021): 6367-6371.

[34] Z. Wang, X. Zou, Y. Xie, et al., “A Nonconjugated Radical Polymer With Stable Red Luminescence in the Solid State,” Materials Horizons 9 (2022): 2564-2571.

[35] X. Zhao, J. Gong, P. Alam, et al., “A Simple Approach to Achieve Organic Radicals With Unusual Solid-State Emission and Persistent Stability,” CCS Chemistry 4 (2022): 1912-1920.

[36] C. Tang, L. Song, K. Zhou, P. Ren, E. Zhao, and Z. He, “Manipulating D-A Interaction to Achieve Stable Photoinduced Organic Radicals in Triphenylphosphine Crystals,” Chemical Science 14 (2023): 1871-1877.

[37] Y. Li, L. Li, Y. Wu, and Y. Li, “A Review on the Origin of Synthetic Metal Radical: Singlet Open-Shell Radical Ground State?,” Journal of Physical Chemistry C 121 (2017): 8579-8588.

[38] Z. Chen, W. Li, Y. Zhang, et al., “Aggregation-Induced Radical of Donor-Acceptor Organic Semiconductors,” Journal of Physical Chemistry Letters 12 (2021): 9783-9790.

[39] Z. Chen, W. Li, M. A. Sabuj, et al., “Evolution of the Electronic Structure in Open-Shell Donor-Acceptor Organic Semiconductors,” Nature Communications 12 (2021): 8559.

[40] X. Chang, M. E. Arnold, R. Blinder, et al., “A Stable Chichibabin Diradicaloid With Near-Infrared Emission,” Angewandte Chemie 63 (2024): e202404853.

[41] M. J. Frisch, G. W. Trucks, H. B. Schlegel, et al., “Gaussian 16 Revision C.02,” (Gaussian, Inc., 2019).

[42] K. Yamaguchi, “The Electronic Structures of Biradicals in the Unrestricted Hartree-Fock Approximation,” Chemical Physics Letters 33 (1975): 330-335.

RIGHTS & PERMISSIONS

2025 The Author(s). Aggregate published by SCUT, AIEI, and John Wiley & Sons Australia, Ltd.