Bidentate pyridyl‐NHC ligands: synthesis, ground and excited state properties of their iron(II) complexes and role of the fac/mer isomerism

International audience; Iron complexes are promising candidates for the development of sustainable molecular photoactive materials as an alternative to those based on precious metals such as Ir, Pt or Ru. These compounds possess metal-ligand charge transfer (MLCT) transitions potentially of high interest for energy conversion or photocatalysis applications if the ultrafast deactivation via lower-lying metal-centred (MC) states can be impeded. Following an introduction describing the main design strategies used so far to increase the MLCT lifetimes, we review some of our latest contributions to the field regarding bidentate Fe(II) complexes comprising N-heterocyclic carbene ligands. The discussion covers all aspects from their synthesis to their characterization via photophysical, electrochemical and computational techniques. The impact of bidentate coordination together with the configuration (facial and meridional isomers) is analysed, finally highlighting the current challenges in this promising area.