Enhanced Resolution in EPR Spectroscopy: Solid para‐Hydrogen Resolves Proton Hyperfine Splitting in the Diphenylphosphinyl Radical
- 1Lehrstuhl für Organische Chemie II Ruhr‐Universität Bochum Bochum Germany
Abstract
The diphenylphosphinyl radical 1 was generated from iododiphenylphosphine by visible‐light photolysis and flash‐vacuum pyrolysis under cryogenic matrix isolation conditions and characterized by IR, UV/Vis, and EPR spectroscopy. In solid para‐hydrogen (p‐H2), photolysis proceeds markedly more efficiently than in argon and affords substantially narrower EPR signals. Simulation of the low‐field wing requires an effective Gaussian broadening of 0.83 G in p‐H2, compared with 1.13 G in normal hydrogen and 4.95 G in argon. This enhanced resolution reveals a seven‐line proton hyperfine envelope that remained unresolved in previous studies of 1 in frozen solutions. Spectral simulations and quantum‐chemical calculations identify 1 as a π‐type radical with pronounced spin localization at phosphorus and additional spin density delocalized over the phenyl rings. Compared with the more rigid dibenzophospholyl radical 4, radical 1 is less stabilized, more conformationally flexible, and exhibits photochemical H‐atom abstraction from molecular hydrogen. Ground‐state and vertical excited‐state calculations exclude a simple thermal or adiabatic photochemical pathway and instead suggest that nonadiabatic or secondary radical‐pair processes contribute to the reaction. These results establish solid p‐H2 as a powerful medium for resolving otherwise inaccessible hyperfine structure in reactive phosphorus‐centered radicals.
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BibTeX
@article{maehara2026enhanced,
title = {{Enhanced Resolution in EPR Spectroscopy: Solid para‐Hydrogen Resolves Proton Hyperfine Splitting in the Diphenylphosphinyl Radical}},
author = {Mika Maehara and Adrián Portela‐González and Kristin Wulff and Julian Eßer and André K. Eckhardt},
journal = {ChemistryEurope},
year = {2026},
month = oct,
doi = {10.1002/ceur.70380},
url = {https://doi.org/10.1002/ceur.70380},
note = {CC BY},
}
RIS
TY - JOUR
TI - Enhanced Resolution in EPR Spectroscopy: Solid para‐Hydrogen Resolves Proton Hyperfine Splitting in the Diphenylphosphinyl Radical
AU - Mika Maehara
AU - Adrián Portela‐González
AU - Kristin Wulff
AU - Julian Eßer
AU - André K. Eckhardt
PY - 2026
DA - 2026/10/30
JO - ChemistryEurope
DO - 10.1002/ceur.70380
UR - https://doi.org/10.1002/ceur.70380
AB - The diphenylphosphinyl radical 1 was generated from iododiphenylphosphine by visible‐light photolysis and flash‐vacuum pyrolysis under cryogenic matrix isolation conditions and characterized by IR, UV/Vis, and EPR spectroscopy. In solid para‐hydrogen (p‐H2), photolysis proceeds markedly more efficiently than in argon and affords substantially narrower EPR signals. Simulation of the low‐field wing requires an effective Gaussian broadening of 0.83 G in p‐H2, compared with 1.13 G in normal hydrogen and 4.95 G in argon. This enhanced resolution reveals a seven‐line proton hyperfine envelope that remained unresolved in previous studies of 1 in frozen solutions. Spectral simulations and quantum‐chemical calculations identify 1 as a π‐type radical with pronounced spin localization at phosphorus and additional spin density delocalized over the phenyl rings. Compared with the more rigid dibenzophospholyl radical 4, radical 1 is less stabilized, more conformationally flexible, and exhibits photochemical H‐atom abstraction from molecular hydrogen. Ground‐state and vertical excited‐state calculations exclude a simple thermal or adiabatic photochemical pathway and instead suggest that nonadiabatic or secondary radical‐pair processes contribute to the reaction. These results establish solid p‐H2 as a powerful medium for resolving otherwise inaccessible hyperfine structure in reactive phosphorus‐centered radicals.
SN - 2751-4765
ER -