A coumarin-based chiral fluorescence sensor for the highly enantioselective recognition of phenylalaninol

Abstract

A chiral host L1 incorporating (S)-BINOL and substituted coumarin moieties was synthesized via a nucleophilic addition–elimination reaction, and ligand L2 could be obtained by the reduction reaction of the imine-based L1 with NaBH4. The fluorescence responses of chiral compounds L1 and L2 on (L)-/(D)-phenylalaninol were investigated by fluorescence spectra. The fluorescence intensity of L1 in cooperation with (L)-/(D)-phenylalaninol shows a gradual enhancement upon addition of (L)-/(D)-phenylalaninol and keeps a nearly linear correlation with the concentration molar ratios from 1 : 10 to 1 : 180. Stoichiometries and association constants of L1 with (L)-/(D)-phenylalaninol were calculated. The results indicate that chiral sensor L1 can exhibit a remarkable “turn-on” fluorescence enhancement response and excellent enantioselective behaviour for (L)-phenylalaninol by direct visual observation at low concentration, and the value of the enantiomeric fluorescence difference ratio (ef) is 3.07. On the contrary, no obvious fluorescence response and enantioselective recognition effect can be detected for L2 towards either (L)-/(D)-phenylalaninol.