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 (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=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). Superlange Lumineszenzlebensdauer bei Raumtemperatur (4500 μs), hohe Quantenausbeute (8.2 %) und reversible Redoxchemie werden mit dem Übergangsmetallkomplex [Cr(tpe)2]3+ durch den Chelat‐Bisswinkel, Inversionssymmetrie und den redoxinaktiven Liganden (tpe=1,1,1‐tris(pyrid‐2‐yl)ethan) ermöglicht. [Cr(tpe)2]3+ ist für lichtinduzierte Energie‐ und Elektronenübertragungsprozesse ähnlich gut geeignet wie die klassischen Edelmetall‐Ionen‐Komplexe.