Probing the photophysical capability of mono and bis(cyclometallated) Fe(ii) polypyridine complexes using inexpensive ground state DFT

Abstract

The abundance and low toxicity of iron with respect to ruthenium would certainly make it valuable for photophysical applications if one could circumvent its tendency to make high-spin compounds and the kinetic lability of its polypyridine complexes, both related to the presence of low-lying quintet metal-centered excited states. The aim of this study was to probe the photophysical potential of six cyclometallated Fe(ii) polypyridine complexes by means of ground state DFT and TDDFT calculations. Quantitative and qualitative indicators were extracted from such calculations and bring us to the conclusion that two complexes should display promising photophysical properties: Fe(NCN)(NNC) and Fe(NNC)2.

Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment

“…Similarly, Dixon and coworkers studied mono-and bis(cyclometalated) iron(II) complexes using DFT calculations. [159][160][161] The 3 MC state in [Fe( pbpy)(tpy)] + with peripheral cyclometalation is substantially higher in energy than in [Fe(dpb)(tpy)] + with central cyclometalation, very similar to the results presented here for the ruthenium homologues. Furthermore, they highlighted, that bis(cyclometalated) iron(II) complexes such as [Fe(dpb)( pbpy)] and [Fe( pbpy) 2 ] have very low-lying 3 MLCT states that are, in the case of [Fe(dpb)( pbpy)], only marginally distorted compared to the ground state geometry.…”

Reversing the relative 3MLCT–3MC order in Fe(ii) complexes using cyclometallating ligands: a computational study aiming at luminescent Fe(ii) complexes

“…6 A mixed Fe(II) complex combining a biscarbene ligand and tpy has been proposed in order to red-shift the absorption of the tetracarbene complex. 11 Two complexes stood out as promising from the photophysical viewpoint: Fe(NNC)(NCN) 6 and Fe(NNC) 2 7. 9 Besides the synthetic tour de force, the 5 MC state is made inaccessible upon 500 nm light excitation but unfortunately the 3 MC state is lower than the 3 MLCT state (albeit much closer than in Fe(tpy) 2 2+ ).…”

NHC-Based Iron Sensitizers for DSSCs

“…However, ruthenium is a scarce, potentially toxic, and expensive metal, limiting the real-world industrial development. This has motivated the quest for valuable alternatives, and among them, earthabundant, low-cost, and environmentally friendly d-block metals such as iron [14][15][16] and copper [17,18] are particularly attractive. Despite an intense MLCT absorption, however, conventional Fe(II) polypyridyl complexes are, unfortunately, characterized by an ultrafast (ca.…”