New Insights into Circularly Polarized Luminescence from Chromium(III) Spin-Flip Emitters.

Circularly Polarized Luminescence (CPL) is emerging as a central tool for chiral photonics, enabling applications ranging from sensing and security inks to circularly polarized organic light-emitting diodes (OLEDs). While most highly developed CPL emitters are organic chromophores, lanthanide complexes, or 4d/5d transition‑metal compounds, recent work has placed kinetically inert chromium(III) polypyridines at the forefront of the field. Their near‑infrared (NIR) metal‑centered 'spin‑flip' emissions produce long-lived and relatively large dissymmetry factors (|glum| ≈ 2·10-1) when chirality is encoded through helically wrapped di‑tridentate ligands. This mini‑review summarizes the physical origin of large CPL in Cr(III) and highlights recent advances in rational tuning of glum and CPL brightness through modifications of the metal-ligand covalency (nephelauxetic effect). Finally, we outline emerging directions including magnetically induced CPL (M-CPL) and the first proof‑of‑concept for Cr(III) complex‑based CP‑NIR‑OLEDs.