Chiral Ionic Covalent Organic Framework as an Enantioselective Fluorescent Sensor for Phenylalaninol Determination

Phenylalaninol (PAL) is a significant chemical intermediatewidelyutilized in drug development and chiral synthesis, for instance, asa reactant for bicyclic lactams and oxazoloisoindolinones. Since theabsolute stereochemical configuration significantly impacts biologicalaction, it is crucial to evaluate the concentration and enantiomericcontent of PAL in a quick and convenient manner. Herein, an effectivePAL enantiomer recognition method was reported based on a chiral ioniccovalent organic framework (COF) fluorescent sensor, which was fabricatedvia one-step postquaternization modification of an achiral COF by(1R, 2S, 5R)-2-isopropyl-5-methylcyclohexyl-carbonochloridate(L-MTE). The formed chiral L-TB-COFcan be applied as a chiral fluorescent sensor to recognize the stereochemicalconfiguration of PAL, which displayed a turn-on fluorescent responsefor R-PAL over that of S-PAL withan enantioselectivity factor of 16.96. Nonetheless, the single L-MTE molecule had no chiral recognition ability for PAL.Moreover, the ee value of PAL can be identified by L-TB-COF. Furthermore, density functional theory (DFT) calculationsdemonstrated that the chiral selectivity came from the stronger bindingaffinity between L-TB-COF and R-PALin comparison to that with S-PAL. L-TB-COF is the first chiral ionic COF employed to identify chiralisomers by fluorescence. The current work expands the range of applicationsfor ionic COFs and offers fresh suggestions for creating novel chiralfluorescent sensors.