Optical properties of transition metal complexes with N-heterocyclic carbenes as ligands. 1,3-di- t-Butylimidazol-2-ylidene as charge transfer donor and acceptor

Abstract

The N-heterocyclic carbene 1,3-di- t-butylimidazol-2-ylidene (dbiy) can function as charge transfer (CT) donor and acceptor if it is coordinated to oxidizing and reducing metals, respectively. The complex Ti IVCl 4(dbiy) 2 shows a ligand-to-metal CT absorption at 450 nm whereas Ni 0(CO) 2(dbiy) 2 is characterized by a metal-to-ligand charge transfer absorption at λ max=365 nm. While Ti IVCl 4(dbiy) 2 is not luminescent, Ni 0(CO) 2(dbiy) 2 displays a room temperature emission at λ max=510 nm which is assumed to originate from the lowest-energy MLCT triplet.