Heteroleptic pyridyl-carbene iron complexes with tuneable electronic properties

New heteroleptic iron complexes mixing a terpyridine bearing a protonable pyridyl substituent (pytpy) and a pyridyl carbene ligand (carb) have been prepared and characterised by UV/Vis spectroscopy, cyclic voltammetry and TD-DFT computations. The absorption spectrum of [Fe(carb)(pytpy)]²⁺ showed a notable redshift compared with the homoleptic [Fe(carb)₂] ²⁺ complex. The MLCT transition occurred at even lower energy when the pendant pyridine was protonated, leading to a wide absorption domain in the 450-650 nm range. Calculations revealed the strong propensity of excited electrons to move from the metal to the pytpy ligand in the complex. This new family of complexes is a promising addition to the arsenal of iron-based chromophores with tuneable electronic properties.