A new iron photo-luminescent compound has been reported in Nature (doi) by a twenty-seven people strong Swedish-Danish-US team with first author Pavel Chábera. In photoluminescence a compound absorbs light and then with a delay emits light again. Many inorganic compounds are known that exhibit this property but none of then based on cheaply available iron. The competition to beat is the well-known tris(bipyridine)ruthenium(II) chloride that absorbs at 452 nm and emits at 620 nm with a lifetime of 700 nanoseconds.
The new iron compound was synthesised in a solution reaction of iron dibromide with an in-situ formed bis- NHC ligand (reaction of a bis(triazolium) bromide with potassium tert-butoxide). The bromine counterions were then replaced by hexafluorophosphate in a reaction with ammonium hexafluorophosphate. With the carbene ligands a switch is made from metal-to-ligand charge-transfer emission (usually short-lived) to ligand-to-metal emission with much better prospects. The results: absorption at 558 nm and emission at 600nm. For now the ruthenium compound mentioned earlier has no need to worry, the emission lifetime for the new iron compound is clocked at just 0,1 nanoseconds.