Bright Long-Lived Circularly Polarized Luminescence in Chiral Chromium(III) Complexes

A series of highly emissive inert and chiral Cr^III complexes displaying dual circularly polarized luminescence (CPL) within the NIR region have been prepared and characterized. The helical [Cr(dqpR)₂ ]³⁺ (dqp=2,6-di(quinolin-8-yl)pyridine; R=OCH₃ , Br or C≡CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC. The corresponding enantiomers show large g_lum ≈0.2 and high quantum yield of up to 17 %, which afford important CPL brightness of up to 170 m^-1  cm^-1 , a key point for applications as chiral luminescent probes. Moreover, the long-lived CP-NIR emission provided by these chromophores (ms range) in aqueous solution opens the way toward the quantification of chiral targets in biological systems with time-gated detection. Thus, such chiral chromophores based on earth abundant and inert 3d metals open new perspectives in the field of CPL and represent an alternative to precious 4d, 5d and to labile 4f metal-based complexes.