Dimer/tetramer motifs determine amphiphilic hydrazine fibril structures on graphite

Abstract

Fibril structures are produced at a solvent-graphite interface by self-assembly of custom-designed symmetric and asymmetric amphiphilic benzamide derivatives bearing C-10 aliphatic chains. Scanning tunnelling microscopy (STM) studies reveal geometry-dependent internal structures for the elementary fibrils of the two molecules that are distinctly different from known mesophase bulk structures. The structures are described by building-block models based on hydrogen-bonded dimer and tetramer precursors of hydrazines. The closure and growth in length of building units into fibrils takes place through van der Waals forces acting between the dangling alkyl chains. The nanoscale morphology is a consequence of the basic molecular geometry, where it follows that a closure to form a fibril is not always likely for the doubly substituted hydrazine. Therefore, we also observe crystallite formation.