Photophysical Integrity of the Iron(III) Scorpionate Framework in Iron(III)-NHC Complexes with Long-Lived 2LMCT Excited States

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  • Om Prakash
  • Linnea Lindh
  • Nidhi Kaul
  • Nils W. Rosemann
  • Iria Bolano Losada
  • Catherine Johnson
  • Pavel Chabera
  • Aleksandra Ilic
  • Jesper Schwarz
  • Arvind Kumar Gupta
  • Jens Uhlig
  • Tore Ericsson
  • Lennart Haggstrom
  • Ping Huang
  • Bendix, Jesper
  • Daniel Strand
  • Arkady Yartsev
  • Reiner Lomoth
  • Petter Persson
  • Kenneth Warnmark

Fe(III) complexes with N-heterocyclic carbene (NHC) ligands belong to the rare examples of Earth-abundant transition metal complexes with long-lived luminescent charge-transfer excited states that enable applications as photosensitizers for charge separation reactions. We report three new hexa-NHC complexes of this class: [Fe(brphtmeimb)2]PF6 (brphtmeimb = [(4-bromophenyl)tris(3-methylimidazol-2-ylidene)borate]- , [Fe-(meophtmeimb)2]PF6 (meophtmeimb = [(4-methoxyphenyl)tris-(3-methylimidazol-2-ylidene)borate] -, and [Fe-(coohphtmeimb)2]PF6 (coohphtmeimb = [(4-carboxyphenyl)tris-(3-methylimidazol-2-ylidene)borate]-. These were derived from the parent complex [Fe(phtmeimb)2]PF6 (phtmeimb = [phenyltris(3-methylimidazol-2-ylidene)borate]- by modification with electron-withdrawing and electron-donating substituents, respectively, at the 4-phenyl position of the ligand framework. All three Fe(III) hexa-NHC complexes were characterized by NMR spectroscopy, high-resolution mass spectroscopy, elemental analysis, single crystal X-ray diffraction analysis, electrochemistry, Mo''ssbauer spectroscopy, electronic spectroscopy, magnetic susceptibility measurements, and quantum chemical calculations. Their ligand-to-metal charge-transfer (2LMCT) excited states feature nanosecond lifetimes (1.6-1.7 ns) and sizable emission quantum yields (1.7-1.9%) through spin-allowed transition to the doublet ground state (2GS), completely in line with the parent complex [Fe(phtmeimb)2]PF6 (2.0 ns and 2.1%). The integrity of the favorable excited state characteristics upon substitution of the ligand framework demonstrates the robustness of the scorpionate motif that tolerates modifications in the 4-phenyl position for applications such as the attachment in molecular or hybrid assemblies.

TidsskriftInorganic Chemistry
Udgave nummer44
Sider (fra-til)17515–17526
Antal sider12
StatusUdgivet - 2022

ID: 325836393