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

A bis(pyrene)-functionalized beta-cyclodextrin (1) has been prepared in two steps from perbenzylated beta-cyclodextrin. This compound shows dual emission properties, which arise from the pyrenyl chromophores. Upon excitation of 1 at 355 rim, monomer blue fluorescence (386, 407 and 428 nm) is observed in DMSO solution, whereas excimer green fluorescence (477 rim) is seen upon addition of >= 20 vol% water in DMSO. This suggests that modified beta-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 (C-7) found in rancid oils and capric acid (C-10), while both monomer and excimer emissions are enhanced by homologous alcohols, such as 1-heptanol, used in cosmetics and I-decanol. Remarkably, bulkier substrates, such as tert-butyl alcohol or 1-adamantylcarboxylic acid are not detected.