Dual emission of a bis(pyrene)-functionalized, perbenzylated β-cyclodextrin

Abstract

A bis(pyrene)-functionalized β-cyclodextrin (1) has been prepared in two steps from perbenzylated β-cyclodextrin. This compound shows dual emission properties, which arise from the pyrenyl chromophores. Upon excitation of 1 at 355 nm, monomer blue fluorescence (386, 407 and 428 nm) is observed in DMSO solution, whereas excimer green fluorescence (477 nm) is seen upon addition of ≥20 vol% water in DMSO. This suggests that modified β-cyclodextrin 1 changes its shape in response to the environment. The sensing properties of 1 towards carboxylic acids and alcohols were investigated in H₂O–DMSO (80 : 20 v/v). Monomer fluorescence is restored selectively by medium length normal carboxylic acids, such as enanthic acid (C₇) found in rancid oils and capric acid (C₁₀), while both monomer and excimer emissions are enhanced by homologous alcohols, such as 1-heptanol, used in cosmetics and 1-decanol. Remarkably, bulkier substrates, such as tert-butyl alcohol or 1-adamantylcarboxylic acid are not detected.