A Helically-Twisted Stereodynamic Probe for Chiroptical Sensing of Chiral Amines through Point-to-Helical Chirality Transmission

Chiral amines and amino alcohols form an important category of molecules employed in the designing of new drugs and catalyst. Herein, we present a helically-twisted stereodynamic dialdehyde probe 1 for the determining of absolute configuration, and enantiomeric excess of chiral amine and amino alcohols. Probe 1 is based on the pyridine-2,6-dicarboxamide (PDC) core and undergoes rapid interconversion between the P- and M- conformers. However, upon imine formation with chiral amines, probe 1 gets locked it in a single conformer majorly. This induces a strong CD signal in addition to changes in the UV-vis and fluorescence signals. The CD spectral change allowed for quantitative enantiomeric excess determination of chiral amines. Circular polarized luminescence (CPL) spectra having the g_lum of 1×10⁻³ was obtained upon imine formation between probe 1 and diamine 2. Single crystal X-ray diffraction studies (SCXRD) confirmed the twisted conformation in 1@(R)-4 and 1@(S)-4, stabilized by intramolecular hydrogen bonding between bound imine nitrogen and proximate amide group.