FeII Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime

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Abstract
The iron carbene complex [FeII(btz)3](PF6)2 (where btz = 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)) has been synthesized, isolated, and characterized as a low-spin ferrous complex. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a 3MLCT state with a 528 ps excited-state lifetime in CH3CN solution that is more than one order of magnitude longer compared with the MLCT lifetime of any previously reported FeII complex. The low potential of the [Fe(btz)3]3+/[Fe(btz)3]2+ redox couple makes the 3MLCT state of [FeII(btz)3]2+ a potent photoreductant that can be generated by light absorption throughout the visible spectrum. Taken together with our recent results on the [FeIII(btz)3]3+ form of this complex, these results show that the FeII and FeIII oxidation states of the same Fe(btz)3 complex feature long-lived MLCT and LMCT states, respectively, demonstrating the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of oxidizing and reducing conditions.
Funding Information
  • Vetenskapsr?det
  • Energimyndigheten
  • Det Frie Forskningsr?d
  • Crafoordska Stiftelsen
  • Knut och Alice Wallenbergs Stiftelse
  • Carl Tryggers Stiftelse f?r Vetenskaplig Forskning
  • Stiftelsen Olle Engkvist Byggm?stare
  • Carlsbergfondet
  • Sten K Johnsons stiftelse
  • LMK-stiftelsen

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