Coumarin carrying Tröger's base analogs exhibiting circularly polarized luminescence

Tröger's base analogs (TBAs) are tertiary diamines with twisted structures and asymmetric nitrogen atoms that can be isolated as enantiopure species. Coumarins are natural occurring oxygen carrying fluorophores with distinct biological and photophysical properties. The present research demonstrates how the combination of the chirality of TBAs and the fluorescence properties of coumarins can generate circularly polarized luminescence (CPL). We report here the preparation, enantiomeric separation, and chiroptical properties of Tröger's base analogs (TBAs) derived from aminocoumarins with methyl or trifluoromethyl group. All three possible TBAs are prepared, identified by nuclear magnetic resonance (NMR) and single crystal X-ray diffraction (SC-XRD), and resolved via chromatography on Whelk-O1 type phase. Absolute configurations of pure enantiomers are determined via SC-XRD and similarity of optical rotation, circular dichroism and CPL spectra. Modest CPL properties with dissymmetry factor ~ 10^-3 were obtained. Additionally, we examined the effect of symmetry in the chiroptical properties of those coumarin-TBAs, and our results suggest that the TBAs subunits should be significantly more differentiated to improve their CPL properties.