Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

Abstract

The structural and electronic strain of ligands promotes the enhancement of the magnitude of circularly polarized luminescence in chiral Eu(iii) complexes.

Remarkable Effects of External Magnetic Field on Circularly Polarized Luminescence of EuIII(hfa)3 with Phosphine Chirality

“…In the ( R , R )‐ and ( S , S )‐pairs of QuinoxP and BenzP , the CPL spectra at J =3 and 4 of Eu III (hfa) 3 are nonideal mirror‐symmetric characteristics (Figure 2(c) and (d)). Similar non‐mirror‐symmetric CPL characteristics of Eu III (hfa) 3 with two other chiral P III ‐ligands, 2,2‐bis(diphenylphosphino)‐1,1‐binaphthalene (BINAP) and 4,12‐bis(diphenylphosphino)‐[2.2]‐paracyclophane (Phanephos), were reported previously by us [25,26] …”

“…Generally, the Eu III ion favors hard bases such as O, N, and F and disfavors soft bases such as P III [25] . However, C 2 ‐symmetric bidentate P III ‐containing ligands with axial chirality and planar chiral ligands, e. g., 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) and 4,12‐bis(diphenylphosphino)‐[2.2]‐paracyclophane (Phanephos) coordinated to Eu III (hfa) 3 (hfa: 1,1,1,5,5,5‐hexafluoroacetylacetonate) in a 1 : 1 molar ratio, have been shown to emit CPL.…”

“…CPL activity from CPL‐inactive Eu III (hfa) 3 complexes is assumed to originate from the C(δ+)−F(δ−)/P III (δ+)−C(δ−) polarity distribution because of the opposite Mulliken charge of outer‐sphere ligand‐ligand interactions [28,29] . The generation of this CPL activity owing to the P III ‐ligand chirality is known as the Pfeiffer effect [25] …”

Unusual Magnetic Field Responsive Circularly Polarized Luminescence Probes with Highly Emissive Chiral Europium(III) Complexes

“…To reveal the chiroptical information in biomacromolecules, such as proteins, cellular organisms, CPL compounds need to be water soluble, stable, highly emissive with large g lum which is difficult to balance simultaneously [8, 11, 43–47] . In our previous studies, [48] our design strategy required 8 chiral centers in order to create a chiral environment to give an optimised g lum (−0.23 at the transition 5 D 0 → 7 F 1 ), but it has simultaneously increased the synthetic difficulties.…”

“…To reveal the chiroptical information in biomacromolecules,s uch as proteins,c ellular organisms,C PL compounds need to be water soluble,s table,h ighly emissive with large g lum which is difficult to balance simultaneously. [8,11,[43][44][45][46][47] In our previous studies, [48] our design strategy required 8c hiral centers in order to create ac hiral environment to give an optimised g lum (À0.23 at the transition 5 D 0 ! 7 F 1 ), but it has simultaneously increased the synthetic difficulties.H ere,i n this simpler design of EuL2-7,weshow that comparable g lum values (Table 2) are possible even by reducing the number of chiral centers to only 4chiral centers by incorporating amore rigid chromophore.T oobtain amore rigid chromophore,the phosphate group was modified to ac arboxyl group and an increased g lum values was achieved as expected.…”