The Excimer Fluorescence of 2-Methylnaphthalene in β- and γ-Cyclodextrin Aqueous Solutions

Abstract 2-Methylnaphthalene (MN) exhibits MN excimer fluorescence in both β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) neutral aqueous solutions. β-CD forms a 1 : 1 inclusion complex with MN, which self-associates to form a 2 : 2 inclusion complex emitting the MN excimer fluorescence. In 0.4 mol dm−3 NaOH solutions, no excimer fluorescence has been observed, indicating that the 2 : 2 inclusion complex dissociates to two 1 : 1 inclusion complexes because of an electrostatic repulsion between the negatively charged hydroxy groups of the two β-CD molecules contained in the 2 : 2 inclusion complex. For the γ-CD–MN system as well as the β-CD–MN system, the excimer fluorescence can be explained in terms of the formation of a 2 : 2 inclusion complex through a self-association of 1 : 1 inclusion complexes.