Deep Eutectic Solvents for Induced Circularly Polarized Luminescence

Abstract

Materials that emit circularly polarized light have application in several important industries. Deep eutectic solvents (DES) with chiral components are attractive as solvents of luminescent lanthanides for the development of chiral light-emitting materials. Deep eutectic solvents are prepared with combinations of tetrabutylammonium (or tetrabutylphosphonium) chloride as hydrogen bond acceptor (HBA) and amino acids, l-and d-glutamic acid, l-proline, and l-arginine as hydrogen bond donor (HBD). A racemic mixture of dissymmetric lanthanide (europium, terbium, and samarium) complexes is dissolved in the DES to measure the induced circularly polarized luminescence (CPL). This resulted in green, orange, and red CPL with a sign that is dictated by the enantiomer of the amino acid in the DES. Thermodynamic measurements show that changing the salt from tetrabutylammonium to tetrabutylphosphonium leads to a 50% increase in the enthalpy and entropy of chiral discrimination. This study demonstrates the capability of chiral DES as a solvent for chiral light-emitting materials and the ability to control this capability through the choice of HBA and HBD.

Assessment of the organocatalytic activity of chiral l-Proline-based Deep Eutectic Solvents based on their structural features

“…A large set of molecules was tested as counterpart of L-Proline (L-Pro) to prepare DESs liquids at room temperature. In this screening, molecules that formed DESs with other counterparts reported in literature were tested, as well as other hydrogen-bond capable molecules; L-Pro was tested as HBA as well as HBD since it is known its dual role [46,47]. Urea, choline chloride, acetamide, (1S)-(+)-10-camphorsulfonic acid, tetramethylammonium chloride, D-(+)-glucose, ZnCl2, 1,6-hexanediol, S-(+)-mandelic acid, picolinic acid, L-(+)-tartaric acid, citric acid and phenol were tested in the molar ratio range from 0.5:1 to 8:1 with L-Pro.…”

Chiral Eutectic Mixtures and Deep Eutectic Solvents for Induced Circularly Polarized Luminescence

“…Among these, there are several examples of applications of DES used as electrolytes in electroluminescent materials, batteries, and electrochromic devices [12–19] . Incorporation of a chiral HBA and/or HBD can lead to their use as solvents for circularly polarized light emitting materials [20,21] …”

“…A number of studies have shown that CPL can be induced through a non‐covalent chiral discrimination interaction between chiral DES, as solvent, and a racemic mixture of luminescent lanthanide complexes, Λ‐ and Δ‐Ln(dpa) 3 3− (where dpa=2,6‐pyridinedicarboxylate dianion, and Ln=Eu 3+ or Tb 3+ ) [20,21] . This coordination complex, Ln(dpa) 3 3− , exists in solution as a racemic mixture of interconverting left‐handed (Λ) or right‐handed (Δ) enantiomers.…”

“…The chiral discrimination interaction is measured using CPL techniques and quantified by the sign (handedness) and magnitude of g em [57,58] . These previous studies primarily focused on the chiral HBD, amino acids and monosaccharides, of the DES to induce CPL, where the achiral HBA was tetrabutylammonium chloride ([TBA]Cl) in most of the chiral DES [20,21] . However, a comparison of 6 : 1 [TBA]Cl vs tetrabutylphosphonium chloride:L‐glutamic acid showed that a change in the HBA produced an observable difference in the magnitude of g em but not the sign [20] .…”

“…These previous studies primarily focused on the chiral HBD, amino acids and monosaccharides, of the DES to induce CPL, where the achiral HBA was tetrabutylammonium chloride ([TBA]Cl) in most of the chiral DES [20,21] . However, a comparison of 6 : 1 [TBA]Cl vs tetrabutylphosphonium chloride:L‐glutamic acid showed that a change in the HBA produced an observable difference in the magnitude of g em but not the sign [20] . This result suggested that while the chiral component is important to controlling chiral discrimination and the induced CPL, the overall structure of the complete DES is also critical.…”