Calix[4]phyrin based redox architectures: towards new molecular tools for electrochemical sensing

New redox active molecular macrocyclic architectures characterized by a direct connection between dipyrrin, tripyrrin and ferrocenyl fragments have been synthesized and characterized. Contrarily to fully conjugated porphyrins, in which four pyrrole moieties contribute to the overall aromatic pi-electronic system and behave as a unique electroactive species, calixphyrins can be regarded as an assembly of independent redox active pyrrole and conjugated oligopyrrole fragments linked through sp(3) hybridized meso carbon atoms. The disruption of the conjugation pathway not only multiplies the number of redox centres throughout the molecule but also leads to a large variety of molecular architectures with specific physico-chemical properties. These novel ferrocene containing hybrid macrocycles exhibit especially attractive electronic and structural features suited for use as molecular sensing tools. An efficient voltammetric sensing of exogenic electron rich anionic species could especially be performed using a metallo-calix[4]phyrin-(1.1.1.1) through the displacement of the labile axial binding site, the perturbation of the Fc(0/+) redox couple being directly related to complexed species features.