Atomic force microscopy study of self-organization of chiral azobenzene derived from amino acid

Abstract

A kind of chiral azobenzene amphiphile, N-[4-(4-dodecyloxyphenylazo)benzoyl]- l-glutamic acid (C 12-Azo- l-Glu; as shown in Fig. 1), was synthesized and the self-organization properties on solid substrates were investigated. C 12-Azo- l-Glu underwent a reversible trans– cis photoisomerization in dilute solution. While the photoisomerization was suppressed on solid substrate because of the H-aggregation, indicating the formation of compact film. When C 12-Azo- l-Glu was cast from ethanol solution onto the hydrophilic surface of mica, a stable flat-layered structure formed spontaneously in large scale. High-resolution images allowed the identification of the relative orientation of molecular rows in the ordered thin film and the crystal lattice of mica. A molecular packing model of the layered structure was proposed. There was a template effect of mica to the self-organization process. Hydrogen bonding, π–π interaction and the chiral center in the molecule played the important roles in the self-organization process. The cooperative competitive effect between them led to the highly ordered structure.