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

Abstract

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 (|g_lum| ≈ 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 g_lum 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.