Excited state dynamics of an air-stable low-spin carbene manganese(III) dual charge transfer chromophore

We report the synthesis, structure and properties of a N-heterocyclic carbene pyridine manganese(III) complex featuring a low-spin ground state. The complex exhibits excellent stability under ambient conditions in the solid state and even dissolved in water. The low-spin ground state is characterized by a large zero-field splitting according to temperature- and field-dependent magnetic susceptibility measurements. Spectroscopic and quantum chemical studies demonstrate that multiple electronic transitions of distinct character are concentrated within a broad absorption band in the visible spectral region. Excitation at various energies across this absorption band and observation of the excited state evolution by ultrafast transient absorption spectroscopy deliver excited-state lifetimes on the picosecond timescale. The short excited state lifetimes are attributed to rapid relaxation to the ground state via distorted excited states. These findings offer new insight into the photophysics of manganese(III) complexes and lay a foundation for the development of photoactive manganese(III)-based chromophores.