Circularly polarized luminescence (CPL) spectroscopy is the emission analogue to circular dichroism (CD) spectroscopy. 1 It is common to report the degree of CPL in terms of the luminescence dissymmetry factor, g lum (λ), which is defined as follows: g lum (λ) = 2ΔI/I = 2 (I L -I R )/(I L + I R ), where I L and I R refer respectively to the intensity of left and right circularly polarized emissions. A value of 0 for g lum corresponds to no circular polarization, while the absolute maximum value is 2. Although the development of useful correlation between CPL spectrum and chiral structure is still limited, 1 a study by Bruce et al. 2 conducted on welldefined DOTA-based macrocyclic Eu(III) complexes led to the following conclusion. The sign and magnitude of CPL are affected by the degree of helical twist of the complex, the nature of the ligand field, and the axial donor group solvation. Of special importance is that the CPL will reflect the time-averaged local helicity around the lanthanide(III) ion (i.e. the magnitude of g lum values increases with an increase in the degree of conformational rigidity of the complex).To date, the largest g lum value reported in the literature was for the commercially available NMR shift reagent tris(3-trifluoroacetyl-(+)-camphorato)europium(III), [Eu((+)-facam) 3 ], in dry DMSO (g lum value of -0.78 at 588.2 nm), 3,4 whereas lanthanidecontaining systems with chiral 2-hydroxyisophthalamide-, pyridyl diamide-,1-hydroxy-2-pyridinone-, or DOTA-based ligand derivatives exhibited g lum values as high as 0.5. 1,4-8 Recently, we reported on the isolation and structural characterization of sodium or cesium tetrakis(3-heptafluorobutylryl-(+)-camphorato) lanthanide(III) complexes, M I [Ln((+)-hfbc) 4 ], by X-ray analysis and/or CD spectroscopy. The solution structure is supposed to take a square antiprism eight coordination (SAPR-8) with Δ-configurational chirality on the basis of the exciton CD spectra. 9,10 In this communication, the CPL as well as CD of M I [Eu((+)-hfbc) 4 ] complexes (M I = Cs and Na) in CHCl 3 and EtOH were examined in order to reveal the detailed chiral configuration in solution. Of special interest is the importance of using CPL for selectively studying only luminescent chromophores present in the systems of interest, in contrast to CD, which is affected by most chromophores and/or equilibrium mixtures in an additive manner. The NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe CPL spectra of 2 mM solutions of M I [Eu((+)-hfbc) 4 ] (M I = Cs and Na) in CHCl 3 are plotted in Figure 1 in the spectral range of the 5 D 0 → 7 F 1 transition, which is particularly wellsuited for CPL measurements since it satisfies the magnetic-dipole selection rule, ΔJ = 0, ±1 (except 0↔0), respectively. As shown in Figure 1, the detection of a CPL signal confirmed the presence of stable chiral emitting species on the luminescence time scale. The g lum values of the M I [Eu((+)-hfbc) 4 ] (M I = Cs and Na) complexes amounted to +1.38 and +0.15 at 595 nm, respecti...

The luminescence and circularly polarized luminescence (CPL) spectra of MI[Eu((+)–hfbc)4] show a similar behavior to the exciton CD in the intraligand π–π* transitions when the alkali metal ions and solvents are manipulated. There is a difference in susceptibility in solvation toward the alkali metal ions but not toward the Eu(III) ion, as in the case of axially symmetric DOTA–type compounds. The remarkable CPL in the 4f–4f transitions provide much more information on stereospecific formation of chiral Eu(III) complexes, since CPL spectroscopy is limited to luminescent species and reflects selectively toward helicity of the local structural environment around the lanthanide(III). While in comparison, exciton CD reveals the chiral structural information from the helical arrangement of the four bladed chelates. Of special importance, the observation of the highest CPL activities measured to date for lanthanide(III)–containing compounds (i.e. Eu and Sm) in solution supports that the chirality of Lanthanide(III) in the excited state corresponds to that in the ground state, which was derived from the exciton CD.

Unprecedented regioselective post-functionalization of racemic and enantiopure cationic diaza [4]helicenes is afforded.

The direct generation of efficient, tunable, and switchable circularly polarized laser emission (CPLE) would have far-reaching implications in photonics and material sciences. In this paper, we describe the first chiral simple organic molecules (SOMs) capable of simultaneously sustaining significant chemical robustness, high fluorescence quantum yields, and circularly polarized luminescence (CPL) ellipticity levels (|glum|) comparable to those of similar CPL-SOMs. All these parameters altogether enable efficient laser emission and CPLE with ellipticity levels 2 orders of magnitude stronger than the intrinsic CPL ones.

The molecular conformation of a bis-helicenic terpyridine system is strongly modified upon binding to Zn(II) ion, a process that is accompanied by large changes in the optical and chiroptical properties. This system affords a new type of helicene-based chiroptical switching.

The chiral nonaazamacrocyclic amine L, which is a reduction product of the 3+3 Schiff base macrocycle, wraps around the lanthanide(III) ions to form enantiopure helical complexes. These Ce(III), Pr(III), Nd(III), Eu(III), Gd(III), Tb(III), Er(III), Yb(III) and Lu(III) complexes have been isolated in enantiopure form and have been characterized by spectroscopic methods. X-ray crystal structures of the Ln(III) complexes with L show that the thermodynamic product of the complexation of the RRRRRR-isomer of the macrocycle is the (M)-helical complex in the case of Ce(III), Pr(III), Nd(III) and Eu(III). In contrast, the (P)-helical complex is the thermodynamic product in the case of Yb(III) and Lu(III). The NMR and CD spectra show that the (M)-helicity for the kinetic complexation product of the RRRRRR-isomer of the macrocycle is preferred for all investigated lanthanide(III) ions, while the preferred helicity of the thermodynamic product is (M) for the early lanthanide(III) ions and (P) for the late lanthanide(III) ions. In the case of the late lanthanide(III) ions, a slow inversion of helicity between the kinetic (M)-helical product and the thermodynamic (P)-helical product is observed in solution. For Er(III), Yb(III) and Lu(III) both forms have been isolated in pure form and characterized by NMR and CD. The analysis of 2D NMR spectra of the Lu(III) complex reveals the NOE correlations that prove that the helical structure is retained in solution. The NMR spectra also reveal large isotopic effect on the 1H NMR shifts of paramagnetic Ln(III) complexes, related to NH/ND exchange. Photophysical measurements show that LRRRRRR appears to favour an efficient 3ππ*-to-Ln energy transfer process taking place for Eu(III) and Tb(III), but these Eu(III)- and Tb(III)-containing complexes with LRRRRRR lead to small luminescent quantum yields due to an incomplete intersystem crossing (isc) transfer, a weak efficiency of the luminescence sensitization by the ligand, and/or efficient non-radiative deactivation processes. Circularly polarized luminescence on the MeOH solutions of Eu(III) and Tb(III) complexes confirms the presence of stable chiral emitting species and the observation of almost perfect mirror-image CPL spectra for these compounds with both enantiomeric forms of L.

Simple organic molecules (SOM) based on bis(haloBODIPY) are shown to enable circularly polarized luminescence (CPL) conforming a new structural design for technologically-valuable CPL-SOMs. The established design comprises, all-in-one, synthetic accessibility, labile helicity, possibility of reversing the handedness of the circularly polarized emission and reactive functional groups, making it unique and attractive as advantageous platform for the development of smart CPL-SOMs.

Two luminescent terbium(III) complexes have been prepared from chiral ligands containing 2-hydroxyisophthalamide (IAM) antenna chromophores and their non-polarized and circularlypolarized luminescence properties have been studied. These tetradentate ligands, which form 2:1 ligand/Tb III complexes, utilize diaminocyclohexane (cyLI) and diphenylethylenediamine (dpenLI) backbones, which we reasoned would impart conformational rigidity and result in Tb III complexes that display both large luminescence quantum yield (Φ) values and strong circularly polarized luminescence (CPL) activities. Both Tb III complexes are highly emissive, with Φ values of 0.32 (dpenLI-Tb) and 0.60 (cyLI-Tb). Luminescence lifetime measurements in H 2 O and D 2 O indicate that while cyLI-Tb exists as a single species in solution, dpenLI-Tb exists as two species: a monohydrate complex with one H 2 O molecule directly bound to the Tb III ion and a complex with no water molecules in the inner coordination sphere. Both cyLI-Tb and dpenLI-Tb display increased CPL activity compared to previously reported Tb III complexes made with chiral IAM ligands. The CPL measurements also provide additional confirmation of the presence of a single emissive species in solution in the case of cyLI-Tb, and multiple emissive species in the case of dpenLI-Tb.