Fluorescence and induced circular dichroism studies on host–guest complexation between γ-cyclodextrin and pyrene

Host–guest complexation between γ-cyclodextrin (γ-CD, cyclo-octa-amylose) and pyrene has been studied in detail by fluorescene and induced circular dichroism (i.c.d.) spectra. γ-CD forms complexes with pyrene with 1 : 1, 1 : 2, 2 : 1, and 2 : 2 stoicheiometries at ambient temperature. The inclusion of pyrene by γ-CD proceeds stepwise; γ-CD including only one pyrene molecule can accommodate a second pyrene molecule to produce a 1 : 2 and/or 2 : 2 complex. Both in a monomolecularly dispersed pyrene solution and in a suspended pyrene solution, several hours are required for γ-CD to include two pyrene molecules. The configuration of two pyrenes included is an S-helix. At temperatures above ca. 85 °C, a 1 : 1 complex alone is formed mainly, where a pyrene molecule is accommodated with its long axis parallel to the axis of γ-CD. The data are compared with those of the systems containing β-CD (cyclohepta-amylose) in place of γ-CD.