Fe(ii) bidentate complexes with long-lived triplet states

Abstract

A series of bidentate quinoline/quinoxaline-NHC ligands were coordinated to an iron(II) metal centre with the aim of taking advantage of the combined effect of NHC σ-donor and quinoline/quinoxaline π-acceptors on the excited-state stabilization of the resulting Fe(II) complexes. Excitation of these complexes at 530 nm promoted excited state formation with lifetimes of up to 74 ps. A detailed study combining spectroelectrochemistry, UV/VIS transient absorption spectroscopy as well as steady-state and time-resolved luminescence concludes that these long-lived triplet states display spectroscopic properties compatible with both MC and MLCT character, with a degree of mixing that depends on the precise ligand structure.