Chiral Molecular Ruby [Cr(dqp)₂]³⁺ with Long-Lived Circularly Polarized Luminescence

Abstract

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.

Simple Perylene Diimide Cyclohexane Derivative With Combined CPL and TPA Properties

“…Organic materials presenting circularly polarized luminescence (CPL) (Riehl and Richardson, 1977;Kumar et al, 2015;Sanchez-Carnerero et al, 2015;Longhi et al, 2016;Tanaka et al, 2018) have recently emerged as promising candidates for advanced optical applications (Zinna et al, 2015;Han et al, 2018;Shi et al, 2018;Zheng et al, 2018;Burrezo et al, 2019;David et al, 2019;Jiménez et al, 2019;Pop et al, 2019;Yang and Zhong, 2019). Thus for example, CPL emitters have been proposed as chiroptical sensors (Staszak et al, 2019), for smart sensing methodologies (Imai et al, 2018;Reine et al, 2018a,b;Zinna et al, 2019), to encode information in light (Andréassons and Pischel, 2018), in patterning processes using security inks (Andres et al, 2014), or constituents of CPL organic lightemitting diodes OLEDs (Brandt et al, 2016;Di Nuzzo et al, 2017).…”

“…Therefore, some efforts have been carried out to combine TPA and CPL (TPCPL) in the same molecule. To our knowledge, very few examples have been described including chiral nanographenic SOMs developed by our group (Cruz et al, 2018a(Cruz et al, ,b, 2019 and chiral Cd(II) 1D structures (Deng et al, 2019). It is remarkable that, up to the moment, there is just one photonic system enabling TPA-induced CPL based on chiral perovskites .…”

Luminescent polypyridyl heteroleptic CrIII complexes with high quantum yields and long excited state lifetimes

“…1 Compared to the microsecond lifetime and high quantum yield (QY) Metal-to-Ligand Charge-Transfer (MLCT) visible emission characterizing optimized Ru II -polypyridyl complexes, 2,3 Cr III embedded in an analogous pseudooctahedral strong ligand-field gives rise to long-lived (reaching the millisecond range) intrashell d-d emission bands showing acceptable quantum yields within the NIR domain. 4,5 These bands correspond to the ruby-like metal-centered Cr( 2 E → 4 A 2 ) and Cr( 2 T 1 → 4 A 2 ) spin-flip transitions occurring within the π Cr (t 2g ) orbitals. These appealing long excited state lifetimes have made Cr III chromophores attractive sensitizers for maximizing the energy transfer in molecular up-conversion using linear optics 6 and for extending the excited state lifetimes of lanthanide ions via downshifting processes.…”

“…These Cr III complexes have been used in a wide range of applications, such as solar cells, 11 in vivo imaging and photodynamic therapy, [12][13][14] sensing, 15,16 ( photo)redox catalysis, [17][18][19][20] light-conversion devices, 6,21,22 and circularly polarized light emitters. 5,23 However, the incorporation of these chromophores into optically active supramolecular devices is limited and still underexplored since it requires the preparation of heteroleptic complexes that can act as "building blocks", an issue solved since several decades for Ru(II) chemistry. 24 In this context, the three-step strategy described by Kane-Maguire and co-workers for the synthesis of heteroleptic [Cr(diimine) 3 ] 3+ , 25 further extended by Constable and co-workers for the synthesis of heteroleptic [Cr(triimine) 2 ] 3+ , 26 relies on the lability of the {Cr-OSO 2 CF 3 } bond that is easily generated by the reaction of the {Cr-Cl} moieties with trifluoromethanosulfonic acid (CF 3 SO 3 H).…”

Enhanced Circularly Polarized Luminescence Activity in Chiral Platinum(II) Complexes With Bis- or Triphenylphosphine Ligands

“…Especially these phosphorescent transition metal complexes, which have remarkable metal-center chirality, tunable emission properties, and unusually high phosphorescence efficiency, are receiving increasing interests in recent years (Han et al, 2018). Such CPL-active materials as Pt (Shen et al, 2014), Ir (Han et al, 2017;Hellou et al, 2017;Yan et al, 2019a), Au (Yang et al, 2020;Zhu et al, 2020), Cu (Jin et al, 2019;Deng et al, 2020;Yao et al, 2020), Zn (Aoki et al, 2017;Chen Y. et al, 2019) Cd (Deng et al, 2019), and Cr (Jiménez et al, 2019) complexes can exhibit various emission colors from blue to red. The dissymmetry factor g lum (g lum = 2 I/I = 2(I L -I R )/(I L + I R ), where I L and I R indicate, respectively, the intensity of the left and right circularly polarized light), can reach up to 10 −2 order.…”