Recent exciting developments in the area of mononuclear photoactive complexes with Earth-abundant metal ions (Cu, Zr, Fe, Cr) for potential eco-friendly applications in (phosphorescent) organic light emitting diodes, in imaging and sensing systems, in dye-sensitized solar cells and as photocatalysts are presented. Challenges, in particular the extension of excited state lifetimes, and recent conceptual breakthroughs in substituting precious and rare-Earth metal ions (e.g. Ru, Ir, Pt, Au, Eu) in these applications by abundant ions are outlined with selected examples. Relevant fundamentals of photophysics and photochemistry are discussed first, followed by conceptual and instructive case studies.

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).