This article aims to show the identity of “CPL-active simple organic molecules” as a new concept in Organic Chemistry due to the potential interest of these molecules, as availed by the exponentially growing number of research articles related to them. In particular, it describes and highlights the interest and difficulty in developing chiral simple (small and nonaggregated) organic molecules able to emit left- or right-circularly polarized light efficiently, the efforts realized up to now to reach this challenging objective, and the most significant milestones achieved to date. General guidelines for the preparation of these interesting molecules are also presented.

Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand.

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 synthesis, characterization, and luminescent behavior of trivalent Sm, Eu, Dy, and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, g lum , recorded for the Eu(III) complex is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments.