Luminescence and Light‐driven Energy and Electron Transfer from an Exceptionally Long‐lived Excited State of a Non‐innocent Chromium(III) Complex

Photoactive metal complexes employing Earth-abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non-innocence to tune the luminescence and photochemistry of the excited state of the [CrN6 ] chromophore [Cr(tpe)2 ](3+) with close to octahedral symmetry (tpe=1,1,1-tris(pyrid-2-yl)ethane). [Cr(tpe)2 ](3+) exhibits the longest luminescence lifetime (tau=4500 mus) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Phi=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)2 ](3+) are redox non-innocent, leading to reversible reductive chemistry. The excited state redox potential and lifetime of [Cr(tpe)2 ](3+) surpass those of the classical photosensitizer [Ru(bpy)3 ](2+) (bpy=2,2'-bipyridine) enabling energy transfer (to oxygen) and photoredox processes (with azulene and tri(n-butyl)amine).