Helically Chiral NHC-Gold(I) Complexes: Synthesis, Chiroptical Properties and Electronic Features of the [5]Helicene-Imidazolylidene Ligand

We describe the preparation of helically chiral gold(I) complexes bearing a [5]helicenic-N-heterocyclic carbene ligand. They were successfully obtained as enantiopure compounds by semi-preparative chiral HPLC and their structural, chiroptical, and photophysical properties were subsequently investigated. Notably, strong electronic circular dichroism, dual emission from singlet and triplet states, with the timescale of the latter up to the millisecond range at room temperature, and moderate circularly phosphorescence were observed. The sigma-donating and pi-accepting properties of the constituent helical ortho-fused pi-conjugated carbene were investigated by classical quantitative analysis of the IR stretching frequencies and NMR characteristics of the corresponding Ir(CO)(2)Cl complex and selenourea.