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PreprintCC BYChemRxiv

High-Spin Diradical-Dominated Chemiluminescence

  • Heng-Ding Wang1,2
  • Ziyan Ye3,4
  • Chiyuan Wei5,6
  • Wei Fang3,4
  • Mingle Li1,2
  • Xiaoqiang Chen1,2
  • Xiaojun Peng1,2
6 affiliations
  1. 1College of Materials Science and Engineering
  2. 2Shenzhen University
  3. 3Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials
  4. 4Fudan University
  5. 5School of Science and Engineering
  6. 6The Chinese University of Hong Kong
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Abstract

We report a quantum-chemical investigation into the chemiluminescence mechanism of cyclometalated Ir (III) Schiff base complexes, promising chemiluminophores for biological imaging. The reaction proceeds via ring-opening of a key oxaziridine intermediate to yield a singlet diradical, which undergoes rapid intersystem crossing (ISC) to its triplet counterpart, followed by deprotonation to generate the emissive triplet product. Within this process, the Ir (III) center not only activates the imine via Lewis-acid coordination but also reverses the singlet-triplet energy ordering of the diradical intermediate, rendering the triplet diradical thermodynamically favored with an equilibrium population of ca. 86% at ambient temperature. The heavy-atom effect of iridium provides substantial spin-orbit coupling; combined with a low-lying minimum-energy crossing point (MECP, 1.7 kcal mol -1 ) and large Franck-Condon-weighted density of states, this accelerates ISC to a rate of 1.5 × 1011 s -1 . Notably, the two radical centers are separated by an 𝑠𝑝3-hybridized carbon, and the intervening C-H bond is strongly polarized by the adjacent O-centered radical, rendering deprotonation nearly barrierless. These collective computational findings establish design principles for two distinct goals: stabilizing diradical species to extend their lifetimes for EPR characterization, and informing the rational development of non-precious-metal chemiluminescent systems.

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Cite

BibTeXRIS
BibTeX
@misc{wang2026highspin,
  title = {{High-Spin Diradical-Dominated Chemiluminescence}},
  author = {Heng-Ding Wang and Ziyan Ye and Chiyuan Wei and Wei Fang and Mingle Li and Xiaoqiang Chen and Xiaojun Peng},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010118/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010118/v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - High-Spin Diradical-Dominated Chemiluminescence
AU  - Heng-Ding Wang
AU  - Ziyan Ye
AU  - Chiyuan Wei
AU  - Wei Fang
AU  - Mingle Li
AU  - Xiaoqiang Chen
AU  - Xiaojun Peng
PY  - 2026
DA  - 2026/10/08
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010118/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010118/v1
AB  - We report a quantum-chemical investigation into the chemiluminescence mechanism of cyclometalated Ir (III) Schiff base complexes, promising chemiluminophores for biological imaging. The reaction proceeds via ring-opening of a key oxaziridine intermediate to yield a singlet diradical, which undergoes rapid intersystem crossing (ISC) to its triplet counterpart, followed by deprotonation to generate the emissive triplet product. Within this process, the Ir (III) center not only activates the imine via Lewis-acid coordination but also reverses the singlet-triplet energy ordering of the diradical intermediate, rendering the triplet diradical thermodynamically favored with an equilibrium population of ca. 86% at ambient temperature. The heavy-atom effect of iridium provides substantial spin-orbit coupling; combined with a low-lying minimum-energy crossing point (MECP, 1.7 kcal mol -1 ) and large Franck-Condon-weighted density of states, this accelerates ISC to a rate of 1.5 × 1011 s -1 . Notably, the two radical centers are separated by an 𝑠𝑝3-hybridized carbon, and the intervening C-H bond is strongly polarized by the adjacent O-centered radical, rendering deprotonation nearly barrierless. These collective computational findings establish design principles for two distinct goals: stabilizing diradical species to extend their lifetimes for EPR characterization, and informing the rational development of non-precious-metal chemiluminescent systems.
ER  -