Abstract
The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter. Typically the constituent particles are considered to be rigid with a fixed shape. Here we show, through a combined experimental and numerical study of the adsorption of cyclic porphyrin polymers, nanorings, on a graphite surface, that flexible molecules can exhibit a rich and complex packing behaviour. Depending on the number of porphyrin sub-units within the nanoring we observe either a highly ordered hexagonal phase or frustrated packing driven by directional interactions which for some arrangements is combined with the internal deformation of the cyclic polymer. Frustration and deformation occur in arrays of polymers with ten sub-units since close packing and co-alignment of neighbouring groups cannot be simultaneously realised for nanorings with this internal symmetry.
Highlights
The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter
We use a combination of ab initio, molecular dynamics (MDs) and coarse graining computational approaches to understand this packing behaviour and to show that similar patterns emerge in computer simulations of deformable nanorings
The nanorings, which have recently been synthesised using a directed selfassembly process[17,18,19,20], consist of an integer number, N, of Zn porphyrin units linked together by butadiyne spacers in a cyclic arrangement
Summary
The regular packing of atoms, molecules and nanoparticles provides the basis for the understanding of structural order within condensed phases of matter. We describe the close-packed assemblies of cyclic porphyrin polymers, referred to as nanorings, which display a frustrated packing in which the internal symmetry competes with the drive to hexagonal order, and individual nanorings responsively modify their shape to maximise local interactions with nearest neighbours. We use a combination of ab initio, molecular dynamics (MDs) and coarse graining computational approaches to understand this packing behaviour and to show that similar patterns emerge in computer simulations of deformable nanorings Both the theoretical and experimental observations show that significant differences occur for nanorings with and without six-fold symmetry in agreement with the expected phase behaviour of disks with sticky patches[16] as recently calculated within a statistical mechanics framework
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