Factorizing the Nephelauxetic Effect in Heteroleptic Molecular Rubies.

The interest in chromium(III) complexes has been renewed over the past decade for the design of efficient earth-abundant phosphorescent red-to-near-infrared spin-flip emitters and photocatalysts with long excited state lifetimes. In this context, we report the energy tuning of spin-flip excited states based on heteroleptic bis(tridentate) polypyridine chromium(III) complexes , namely, , and with the tridentate ligands L and L [X/Y = NMe, ,'-dimethyl-,'-dipyridin-2-ylpyridine-2,6-diamine; X/Y = CH, 2,6-bis(2-pyridylmethyl)pyridine and X/Y = S, 2,6-bis(pyridine-2-ylthio)pyridine]. The heteroleptic complexes are obtained via a novel synthetic approach toward the required intermediate labile triflato complexes Cr(L)(OTf) () from the respective chlorido precursors CrCl(L) () using trimethylsilyl trifluoromethanesulfonate. Spin-flip energies were experimentally detected by vis/near-infrared absorption and emission spectroscopy as well as computationally derived by multireference calculations. Together with the known homoleptic molecular ruby complexes, the three resulting series of luminescent complexes // allow delineation of an additive nephelauxetic effect of the ligands with chromium(III) ions and thus prediction of spin-flip emission energies of derived molecular rubies.