Deep Eutectic Solvents for Induced Circularly Polarized Luminescence

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.