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 mu s) 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).