Dye inclusion single crystals: Preparations, structures and functions

The dyes which have the large πsystem easily associate themselves. To inhibit their π-π stacking, host-guest interaction with cyclodextrins are often employed in water medium. Porphyrins and fullerenes are such typical dyes as guest molecules. Still there are many reports for their host-guest interactions, the structures of their inclusion complexes have been discussed only on the basis of the theoretical calculations and the spectral properties in solution, e.g. NMR and absorption spectra. It is really surprising that, so far, nobody knows the real complex structure determined from single-crystal analysis. In 2011, we reported the first successfulisolation of a dye inclusion single crystal (DISC) between trimethyl-Β-cyclodextrin (TMΒCD) and tetrapyridyl porphyrin, and analyzed its X-ray crystal structure. It revealed the real complex structure which has the prospective barrel shape bicapped complex. Furthermore, the X-ray crystal structure provided several newly information in the molecular conformation. Recently, several crystal structures of dye inclusion complexes using cyclodextrin were reported from other groups. The crystallography of dye inclusion complex should invite the new field of functional materials designed by supramolecular chemistry.