A low-spin manganese(ii) complex with an emissive charge-transfer excited state

Abstract

Manganese is an attractive earth-abundant metal for chromophores because it has multiple oxidation states, making it well-suited for photochemical applications involving electron transfer reactivity. Unfortunately, the tendency of manganese(II) to form high-spin complexes with metal-centered excited states has limited its viability. Herein, we disclose an air-stable Mn(II) complex with N-heterocyclic carbene ligands. Spectroscopy revealed panchromatic absorption with two main bands in the visible region (with maxima at 480 nm and 580 nm), which have mixed charge-transfer and metal-centered character. Excitation into the low-energy band leads to an emissive state with a maximum at 770 nm (QY = 5.7 × 10⁻⁴). Time-resolved emission spectroscopy revealed biphasic kinetics for the ground state recovery and a lifetime of 480 ps.