Exploration of Solvent Effects on the Mechanism of the Pfeiffer Effect

The goal of this research project was to gain a more thorough understanding of how the Pfeiffer effect functions at the molecular level. We also wanted to gain a better understanding of how significant of a role solvent effects, particularly chirality transfer mechanisms, play in the mitigation of the discriminatory interactions between the added chiral species (i.e. L-serine) and the [Ln(DPA)3]3- complex. The Pfeiffer effect is observed when an optically active compound such as an amino acid is introduced to a solution containing a labile racemic metal complex leading to an equilibrium shift. The “perturbation” results in an excess of one enantiomer over the other. The shift is a result of a preferential outer sphere interaction between the introduced chiral species and one enantiomeric form ( or ) of the lanthanide complex. The speculations regarding the actual mechanism of the Pfeiffer effect tend to fall short of an accurate and complete description of the mechanism; one usually attributes the effect to a singular factor such as pH, solvent polarity, or numerous other intermolecular interactions. Through the use of the lanthanide (III) complexes [Tb(DPA)3]3- and [Eu(DPA)3]3- (where DPA= 2,6-pyridinedicarboxylate) and the amino acids L-serine and L-proline, it is becoming clear that it is not so simply described. The true mechanism is far more complicated than to attribute just a singular factor. In order to better understand the mechanism, the solvent environment must first be understood in greater detail

Strong Circularly Polarized Luminescence from Highly Emissive Terbium Complexes in Aqueous Solution

Two luminescent terbium(III) complexes have been prepared from chiral ligands containing 2-hydroxyisophthalamide (IAM) antenna chromophores and their non-polarized and circularly-polarized luminescence properties have been studied. These tetradentate ligands, which form 2:1 ligand/Tb{sup III} complexes, utilize diaminocyclohexane (cyLI) and diphenylethylenediamine (dpenLI) backbones, which we reasoned would impart conformational rigidity and result in Tb{sup III} complexes that display both large luminescence quantum yield ({phi}) values and strong circularly polarized luminescence (CPL) activities. Both Tb{sup III} complexes are highly emissive, with {phi} values of 0.32 (dpenLI-Tb) and 0.60 (cyLI-Tb). Luminescence lifetime measurements in H{sub 2}O and D{sub 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{sub 2}O molecule directly bound to the Tb{sup 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{sup 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

The Importance of Solvent Effects on the Mechanism of the Pfeiffer Effect

The Pfeiffer effect is observed when an optically active compound such as an amino acid is introduced to a solution containing a labile racemic metal complex, and an equilibrium shift is obtained. The “perturbation” results in an excess of one enantiomer over the other. The shift is a result of a preferential outer sphere interaction between the introduced chiral species and one enantiomeric form (Λ or ∆) of a labile metal complex. Speculations regarding the mechanism of the Pfeiffer effect have attributed observations to a singular factor such as pH, solvent polarity, or numerous other intermolecular interactions. Through the use of the lanthanide(III) complexes [Tb(DPA)3]3− and [Eu(DPA)3]3− (where DPA = 2,6-pyridinedicarboxylate) and the amino acids l-serine and l-proline; it is becoming clear that the mechanism is not so simply described as per the preliminary findings that are discussed in this study. It appears that the true mechanism is far more complicated than the attribute just a singular factor. This work attempts to shine light on the fact that understanding the behavior of the solvent environment may hypothetically be the key to offering a more detailed description of the mechanism

Chiral Organic Dyes Endowed with Circularly Polarized Laser Emission

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 (|g|) 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. (Figure Presented).Peer Reviewe

Conformational changes and chiroptical switching of enantiopure bis-helicenic terpyridine upon Zn2+binding

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

Functionalized cationic [4]helicenes with unique tuning of absorption, fluorescence and chiroptical properties up to the far-red range

Unprecedented regioselective post-functionalization of racemic and enantiopure cationic diaza [4]helicenes is afforded. The peripheral auxochrome substituents allow a general tuning of the electrochemical, photophysical and chiroptical properties of the helical dyes (26 examples). For instance, electronic absorption and circular dichroism are modulated from the orange to near-infrared spectral range (575–750 nm), fluorescence quantum efficiency is enhanced up to 0.55 (631 nm) and circularly polarized luminescence is recorded in the red (|glum| ∼ 10−3)