Fluorophore-appended calix[4]pyrroles: Conformationally flexible fluorometric chemosensors

초록

Calix[4]pyrroles bearing appended pyrenyl groups at the meso-positions on one side of the calix[4]pyrrole have been synthesised and characterised. These species act as hosts that exhibit a selective increase in their fluorescence intensity upon the addition of Pb2+ or Cu2+. When excess chloride anion is added after subjecting the host to pre-complexation with Pb2+, the cation-induced enhancement in fluorescence is sustained. On the contrary, no changes in fluorescence are observed when the calix[4]pyrrole host is first treated with chloride anion, followed by the addition of Pb2+. These results are consistent with pre-complexation of Pb2+ not serving to inhibit the binding of chloride anion, while, by contrast, the initial interaction between a chloride anion and the calix[4]pyrrole cavity acts to inhibit the subsequent binding of Pb2+, possibly due to anion-binding-based constraints on the conformational flexibility. [image omitted].

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