Mixed diacetylene/octadecyl melamine nanowires formed at the air/water interface exhibit unique structural and colorimetric properties.

Abstract

Polydiacetylene (PDA) assemblies exhibit interesting photophysical properties, specifically, visible colorimetric transformations. A considerable body of work has focused on the formation and characterization of PDA Langmuir monolayer systems, and the overwhelming majority of reports so far have indicated that the adoption of 2D sheetlike structures associated with a hydrogen bond network between the diacetylene headgroups is a prerequisite for polymerization and chromatic properties. Here we report for the first time on the assembly of nanowire networks in mixed Langmuir monolayers comprising diacetylene monomers and octadecyl melamine surfactants. Structural and physical analysis indicates that the nanowires are composed of a helical organization of stacked diacetylene/octadecyl melamine building blocks assembled through hydrogen bonds between the melamine residues and the carboxylic termini of the diacetylenes. Following ultraviolet-induced polymerization, the PDA/octadecyl melamine nanowires exhibited unusual chromatic properties, specifically, an absence of the ubiquitous "blue" phase, rather transforming into a new "purple" PDA phase. This study demonstrates that the incorporation of surfactant constituents within diacetylene frameworks provides a means for modulating the structural and chromatic features of PDA assemblies, giving rise to new morphologies and unique optical properties.