Exceptional Excited-State Lifetime of an Iron(II)-N-Heterocyclic Carbene Complex Explained

Lisa A. Fredin, Mátyás Imre Pápai, Emese Rozsalyi, Gyoergy Vanko, Kenneth Wärnmark, Villy Sundström, Petter Persson

Research output: Contribution to journalJournal articleResearchpeer-review


Earth-abundant transition-metal complexes are desirable for sensitizers in dye-sensitized solar cells or photocatalysts. Iron is an obvious choice, but the energy level structure of its typical polypyridyl complexes, featuring low-lying metal-centered states, has made such complexes useless as energy converters. Recently, we synthesized a novel iron-N-heterocyclic carbene complex exhibiting a remarkable 100-fold increase of the lifetime compared to previously known iron(II) complexes. Here, we rationalize the measured excited-state dynamics with DFT and TD-DFT calculations. The calculations show that the exceptionally long excited-state lifetime (similar to 9 ps) is achieved for this Fe complex through a significant destabilization of both triplet and quintet metal-centered scavenger states compared to other Feu complexes. In addition, a shallow (MLCT)-M-3 potential energy surface with a low-energy transition path from the (MLCT)-M-3 to (MC)-M-3 and facile crossing from the (MC)-M-3 state to the ground state are identified as key features for the excited-state deactivation.
Original languageEnglish
JournalThe Journal of Physical Chemistry Letters
Issue number12
Pages (from-to)2066-2071
Number of pages6
Publication statusPublished - 2014
Externally publishedYes


  • Fe-II complexes
  • N-heterocyclic carbene
  • Density functional theory
  • Potential energy surfaces
  • Excited-state dynamics


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