Synthesis of phenylacetylene macrocycles and macrobicycles and their organization in solution, at the air-water interface and on solid surfaces

Abstract

This dissertation outlines the synthesis of phenylacetylene macrocycles and macrobicycles. The aggregation of these molecules in solution and their organization at the air-water interface on solid surfaces are also studied. The efficient method for synthesizing linear or branched sequences of phenylacetylene oligomers allows the placement of various functional groups at any specific positions along the sequence chain. These phenylacetylene sequences are cyclized to give phenylacetylene macrocyclic (PAMs) and macrobicyclic compounds (BIPAMs) in high yields. Amphiphilic compounds were obtained by performing simple transformation of the functional groups on these PAMs and BIPAMs.

Aromatic $\pi$-$\pi$ interactions induce the self-association of certain phenylacetylene macrocycles. PAMs substituted with electron withdrawing groups (e.g. esters) are more strongly associated than those bearing electron donating groups (e.g. alkyl ethers) or macrocycles bearing a combination of the two substituents. Endo-annular alkyl ethers as well as branched exo-annular alkyl esters severely disrupt aggregation. Consideration was also given to $\pi$-$\pi$ interactions between aromatic and ethynyl groups and between a pair of acetylenes but these were concluded to be less significant based on an analysis of data from the Cambridge Structural Database.

Finally, the behavior of amphiphilic macrocycles and macrobicycles, that differ in terms of the nature and orientation of their pendant functional groups, are probed using the Langmuir-Blodgett technique at the air-water interface and the resulting monolayers transferred to substrates. Macrocycles that have spatially segregated hydrophilic and hydrophobic groups adopt the predicted "edge-on" orientation. The Pressure-Area isotherms of the monolayers formed by the macrobicycles indicate that they assemble in a predicted hexagonal lattice. These monolayers were characterized with a wide variety of techniques such as contact angle measurements, UV-vis, FTIR, Raman, X-ray photoelectron spectroscopy and ellipsometry, each of which provided some information about film structure, composition and organization of the molecules.