Selective Fluorimetric Detection of Primary Alkylamines by a Calix[6]arene Funnel Complex

The association of host-guest and coordination chemistry was used to develop a fluorescent molecular sensor. A calix[6]arene bearing three imidazole arms at the small rim and three quinoline fluorophores at the large rim was synthesized and characterized. A two-step coordination sequence was observed upon addition of Zn^II . The first Zn^II center binds the tris-imidazole small rim site, leading only to a small perturbation of the fluorescence. In contrast, a large bathochromic shift is observed upon binding of the second Zn^II center at the large rim as a result of the direct interaction of Zn^II with the quinoline fluorophores. The system acts as a selective receptor for primary amines. Host-guest adduct formation could be identified by a shift and enhancement of the fluorescence emission that is dependent on the length and shape of the primary amine. This system constitutes a fluorescent reporter with a selective response among primary amines.