Two-dimensional self-assembly of diacetylenic acid derivatives and their light-induced polymerization on HOPG...

The bottom-up fabrication of molecular nanodevices will require precise (photo)-control over self-assembled interfacial structures. Here, the self-assembly and photopolymerization behaviors of six diacetylenic acid derivatives on highly oriented pyrolytic graphite (HOPG) surfaces are studied by using scanning tunneling microscope (STM). The van der Waals interaction among alkyl chains is the predominant driving force for determining the varied assembly structure. Diacetylenic acid derivatives with the diacetylene moiety directly connected to the carboxyl group (2,4-heptadecadiynoic acid (C₁₇H₂₆O₂), 2,4-nonadecadiynoic acid (C₁₉H₃₀O₂) and 2,4-heneicosadiynoic acid (C₂₁H₃₄O₂)) assemble to form surface monolayers with lamella-like structures where the alkyl chains interdigitate. Moreover, diacetylenic acid derivatives with the diacetylene group located in the middle of the side chains and far from the carboxyl group (10,12-tricosadiynoic acid (C₂₃H₃₈O₂), 10,12-pentacosadiynoic acid (C₂₅H₄₂O₂) and 10,12-heptacosadiynoic acid (C₂₇H₄₆O₂)) tend to assemble into paralleled structures with the alkyl chains adopting a tail-to-tail assembly mode. This work thus elucidates in detail the structure-function relationships for photo-modifiable self-assembled interfacial nanostructures based on diacetylenic acid.