Synthesis and study of a cyclophane displaying dual fluorescence emission: a novel ratiometric sensor for carboxylic acids in organic medium

The synthesis and fluorescent properties of a novel cyclophane containing two l-valine units and one naphthalene chromophore are described. Synthesis of the macrocycle 1 was accomplished without using high-dilution methods in moderate to high yields. The fluorescence spectrum of 1 in neutral dichloromethane shows a band at 390 nm attributable to emission from an exciplex formed between the naphthalene unit and the neighboring amine groups. Addition of trifluoroacetic acid restores the typical naphthalene emission at 330 nm. Due to the fact that both emissions have similar intensities under the working conditions, the ratio between them can be used to obtain a ratiometric response to carboxylic acids in organic medium.