Forbidden crystals: Penrose tiling with molecules

Abstract

Since the first discovery of quasicrystals by mathematicians in the 1960s, quasicrystalline patterns which possess unusual symmetric orders have become an issue among mathematicians. Observation of 5-fold crystal symmetry in metal alloys in 1984 has attracted other scientists. Penrose tiling is the simplest quasicrystal comprised of only pentagon motifs. Although quasicrystals have been observed in alloys and soft matter states (polymers, colloids), no one has yet successfully generated full molecular quasicrystals. Only small pieces of molecular Penrose tiling have been reported. We are working on this challenge by using molecules with 5-fold symmetry as molecular ‘tiles’ to create 2-dimensional molecular Penrose tilings. Alignment of the tiles is the key to creating the quasicrystalline pattern. Possible candidates as tiles which must be synthetically accessible are croconate and its derivatives, macrocycles such as campestarene and supramolecules such as cucurbituril. The techniques of coordination and supramolecular chemistry will direct the ordering of the tiles. After deposition of the synthesised tiles on substrates, surface imaging (STM and AFM) and analytical techniques (XPS, LEED, GI-SAXS) will be used to investigate the resulting films.