Excimer formation of 1-chloronaphthalene in alkaline aqueous solutions containing γ-cyclodextrin or maltosyl-γ-cyclodextrin

Abstract

1-Chloronaphthalene (1CN) forms inclusion complexes with γ-cyclodextrin (γ-CD) and maltosyl-γ-CD (G2-γ-CD) in neutral and 0.4 mol dm⁻³ NaOH solutions. In 0.4 mol dm⁻³ NaOH solution as well as in neutral solution, excimer fluorescence of 1CN was observed in the presence of γ-CD (or G2-γ-CD), although the intensity of the excimer fluorescence in alkaline solution was weaker than that in neutral solution. The excimer fluorescence in alkaline solution is due to the 2 : 2 γ-CD (G2-γ-CD)–1CN inclusion complex, which is of a different type from that of the 2 : 2 inclusion complex responsible for excimer fluorescence in neutral solution. In the 2 : 2 inclusion complex in neutral solution, the secondary hydroxy-group sides of the CD cavities are connected to each other through hydrogen bonds. In the 2 : 2 inclusion complex in alkaline solution, on the other hand, the primary hydroxy-group sides of the CD cavities face each other. The equilibrium constants for the formation of the 1 : 1 and 2 : 2 inclusion complexes of γ-CD (G2-γ-CD) with 1CN have been evaluated from the fluorescence intensity variations with an increase in the concentration of γ-CD (G2-γ-CD).