The chiral resolution of a kinetically inert molecular ruby [Cr(dqp)2] 3+ (1, dqp = 2,6-di(quinolin-8-yl)pyridine) displaying strong dual light emission at room temperature has been achieved. The wrapped arrangement of the sixmembered dqp chelating ligands around the Cr(III) provided non-planar helical conformations leading to the diastereoselective assembly of chiral bis-tridentate monometallic Cr(III)-helix. The PP-(+)-[Cr(dqp)2] 3+ and MM-(-)-[Cr(dqp)2] 3+ enantiomers could be separated and isolated by using cation-exchange chromatography and subsequent saltmetathesis with KPF6. X-Ray crystallographic analysis based on Flack parameters assigned the absolute configurations of the two enantiomers. Circularly Polarized Luminescence (CPL) spectra showed two polarized emission bands within the NIR region corresponding to the characteristic metal-centered spin-flip Cr(2 E→ 4 A2) and Cr(2 T1→ 4 A2) transitions with exceptionally high dissymmetry factors, glum, of 0.2 and 0.1, respectively, which are comparable to those reported for rareearth chiral complexes. Photophysical properties also revealed an extremely long excited-state lifetime of 1.2 ms and a high quantum yield of 5.2% at room temperature in water. These properties make [Cr(dqp)2] 3+ an ideal sensitizer for the preparation of enantiopure luminescent supramolecular energy-converting devices and also open up the possibility of using chiral Cr(III) chromophores for the construction of NIR-CPL materials and polarized photonic devices based on earthabundant metals.

The combination of π‐donating amido with π‐accepting pyridine coordination units in a tridentate chelate ligand causes a strong nephelauxetic effect in a homoleptic CrIII complex, which shifts its luminescence to the NIR‐II spectral range. Previously explored CrIII polypyridine complexes typically emit between 727 and 778 nm (in the red to NIR‐I spectral region), and ligand design strategies have so far concentrated on optimizing the ligand field strength. The present work takes a fundamentally different approach and focusses on increasing metal–ligand bond covalence to shift the ruby‐like 2E emission of CrIII to 1067 nm at 77 K.

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor ( g lum ), which can reach the maximum values of −2 ≤ g lum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10 −5 ≤ g lum ≤ 10 −3 ). However, recent efforts in this field show that g lum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral Eu III - and Sm III -based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with g lum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f–f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral Cr III -based complexes that reach values of g lum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications.

As eries 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= OCH 3 ,B ro rC CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC.T he corresponding enantiomers show large g lum % 0.2 and high quantum yield of up to 17 %, whichaffordimportant CPL brightness of up to 170 m À1 cm À1 ,akey point for applications as chiral luminescent probes.M oreover,t he long-lived CP-NIR emission provided by these chromophores (ms range) in aqueous solution opens the way towardt he quantification of chiral targets in biological systems with timegated detection. Thus,s uch 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.

Nine-coordinate [ErN9] or [ErN3O6] chromophores found in triple helical [Er(L)3]3+ complexes (L corresponds to 2,2’,6’,2”-terpyridine (tpy), 2,6-(bisbenzimidazol-2-yl)pyridine (bzimpy), 2,6-diethylcarboxypyridine (dpa-ester) or 2,6-diethylcarboxamidopyridine (dpa-diamide) derivatives), [Er(dpa)3]3- (dpa is the 2,6-dipicolinate dianion)...