Azocalix[4]arene-based chromogenic anion probes

Azocalix[4]arene derivatives 1-5, with one or two azophenol chromophores and different binding sites, were found to allow not only for high selective and sensitive colorimetric detection but also easy colorimetric differentiation of F-, AcO- and H2PO4-, of similar basicity, depending upon the azocalix[4]arene structure, guest basicity and conformational complementarity between the host and guest.