Shape Amphiphiles in 2-D: Assembly of 1-D Stripes and Control of Their Surface Density

Abstract

The morphology of monolayers assembled from mixtures of a shape-amphiphilic molecule, {33,19} = 1-((hentriaconta-14,16-diyn-1-yloxy)methyl)-5-((heptadecyloxy)methyl)anthracene, and a symmetric molecule, {192}, at the solution-HOPG interface depends strongly on the components' solution concentrations and sample annealing history. The kinked alkadiyne side chain, {33}, packs optimally only with antiparallel aligned, {33} side chains. Thus, optimal packing of {33} side chains should assemble "{33} stripes" consisting of two adjacent {33,19} columns with interdigitated {33} chains. The aliphatic {19} side chain of {33,19} can pack with antiparallel aligned {19} side chains from {192} or from {33,19}. Thus, {33} stripes can incorporate as "guests" within {192} "host" monolayers. The composition and morphology of monolayers formed by drop casting solutions of {33,19} and {192} at 19 °C are dominated by assembly kinetics. Short {33} strips are immersed haphazardly in monolayers comprised mostly of {192}. Thermal annealing promotes fuller expression of {33,19}'s shape amphiphilicity and assembly of thermodynamically determined monolayers incorporating 1-D {33} stripes within a 2-D matrix of {192}. Larger solution mole fractions of {192} yield annealed monolayers with nearly constant {33} strip lengths, decreased {33} strip density, and increased {33} strip spacing.