Circularly Polarized Luminescence of Aluminum Complexes for Chiral Sensing of Amino Acid and Amino Alcohol.

Determination of the absolute configuration (AC) of chiral molecules is a key issue in many fields related to chirality such as drug development, the asymmetric reaction screening, and the structure determination of natural compounds. Although various methods, such as X-ray crystallography and NMR spectroscopy, are used to determine the AC, a simple and cheap alternative method is always anticipated. So far, electronic circular dichroism (ECD) spectroscopy has been widely used to ascertain the AC and enantiomeric excess (ee) values by applying appropriate organic probes. Here, circularly polarized luminescence (CPL) spectroscopy was applied to determine the AC and ee values of a series of amino acid and amino alcohol. The measurements were conducted by mixing the amino acids or amino alcohols with an achiral 1-hydroxy-2-naphthaldehyde. Upon in situ formation of the Schiff base complexes, the system showed emission enhancement and CPL in the presence of Al3+ , whose intensity and sign can be used to assign the chiral sense of the amino acids and amino alcohols. The authenticity of the method was further compared with the established CD spectroscopy, revealing that CPL spectra of formed Al3+ complex were effective to determine the AC of chiral species.