A Low-Spin Manganese (II) Complex with an Emissive Charge-Transfer Excited State

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 S = ½ 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. Each band produces a unique emission spectrum in the range of 600-800 nm upon excitation. In both cases, time-resolved emission spectroscopy revealed biphasic kinetics for the ground state recovery, with a lifetime of 1 ns at 620 nm.