Monolayer Formation and Chiral Recognition of Binaphthyl Amphiphiles at the Air–Water Interface

Abstract

Abstract In this study, we designed a new monolayer-forming material, 2, 2′-bis(octadecyloxy)-1, 1′-binaphthyl-6, 6′-dicarboxylic acid (BNOC), which has axial chirality derived from the binaphthyl moiety with two COOH groups. Because the axial chirality of the binaphthyl group occupies a larger asymmetric space than the central chirality, the arrangement of the binaphthyl derivative is expected to show a characteristic structure at the air–water interface. In addition, BNOC has two carboxyl groups, which may form intermolecular hydrogen bonds. We carried out the structural analyses of racemic and optically active BNOC monolayers using surface pressure–area isotherms in parallel with Brewster angle microscopy and atomic force microscopy (AFM). Our results indicated that (±)-BNOC forms a solid film while (S)-BNOC forms a liquid film. Moreover, AFM structural analysis revealed that the real lattices of both monolayers differ significantly. These structural differences are attributed to the steric regularity resulting from the axial chirality, which causes a difference in the mode of intermolecular interaction between the two monolayers.