Stereoisomer library prepared via controlled radical polymerization: isolation, structural identification and discovery of stereospecific gelation behaviour of tri(N-phenyl acrylamide)

Abstract

The construction of stereoisomer libraries is essential for designing, maximizing, and tuning the biological, self-assembly, and photoelectromagnetic properties of optically active molecules. In this study, a stereoisomer library consisting of all eight stereoisomers of a vinyl oligomer, a trimer of phenyl acrylamide (tri(PAAm)), was prepared by a one-pot controlled radical polymerization reaction followed by two-step column chromatography. Tacticity of each isomer, i.e., the relative stereochemistry of three chiral centers within tri(PAAm), was assigned using proton nuclear magnetic resonance (¹H-NMR) and circular dichroism (CD) spectra. Interestingly, one stereoisomer self-assembled and formed an organo-gel. The control experiments revealed that the assembly was driven via configuration-dependent intermolecular hydrogen bonding and π–π interaction. The absolute structure of the gelled tri(PAAm) was identified by combining the tacticity data with the CD spectra and an electronic CD spectrum calculated by density functional theory (DFT). Stereoisomer libraries easily prepared via one-pot radical polymerization are promising modalities for supramolecular chemistry, pharmaceuticals, and photoelectromagnetic materials.