Manganese(i) complexes with metal-to-ligand charge transfer luminescence and photoreactivity

Abstract

Precious metal complexes with the d 6 valence electron configuration often exhibit luminescent metal-to-ligand charge transfer (MLCT) excited states, which form the basis for many applications in lighting, sensing, solar cells, and synthetic photochemistry. Iron(II) has received much attention as a possible Earth-abundant alternative, but to date no iron(II) complex has been reported to show MLCT emission upon continuous-wave excitation. Manganese(I) has the same electron configuration as iron(II), but had typically been overlooked in the search for cheap MLCT luminophores until now. Here we report that isocyanide chelate ligands give access to air-stable manganese(I) complexes that exhibit MLCT luminescence in solution at room temperature. These compounds were successfully used as photosensitizers for energy-and electron-transfer reactions and were shown to promote the photoisomerization of trans-stilbene. The observable electron transfer photoreactivity occurred from the emissive MLCT state, whilst the triplet energy transfer photoreactivity originates from a ligand-centered 3 π-π* state.

Luminescent chromium(0) and manganese(i) complexes

“…2a ) resulted in the first examples of MLCT-luminescent manganese complexes in solution at room temperature. 21 Previously, only a molecular complex of manganese( iv ) with luminescence properties has been reported, however, this compound was reported to emit primarily in the solid state and not from an MLCT state. 53 Both [Mn(L bi ) 3 ] + and [Mn(L tri ) 2 ] + ( Fig.…”

Phototherapeutic anticancer strategies with first-row transition metal complexes: a critical review

“…Yet, a study presenting Mn(I) complexes with long enough LMCTs suitable for triplet-triplet energy transfers was recently published, which gives hope for the design of type II PDT agents. 71…”

The overlooked NIR luminescence of Cr(ppy)3

“…fac -Cr(ppy) 3 is the first Cr III spin–flip emitter with emission above 900 nm in solution at 293 K. The effect of carbanionic donors in place of pyridine donors is two-fold, namely the increase in energy of the metal centred quartet states, owing to the larger ligand field strength, and the decrease of the energy of the spin–flip states, owing to the stronger Cr–C bond covalence (nephelauxetic effect). These insights on the photophysics of the cyclometalated Cr III complex fac -Cr(ppy) 3 are complementary to recent discoveries for first row transition metal CT emitters 7,48–54 and demonstrate that fundamental ground-breaking studies can pave the way to fully exploiting Earth-abundant metals, e.g. in light harvesting, sensing, photocatalysis and optical devices.…”