Methylazacalix[4]pyridine:: En route to Zn2+-specific fluorescence sensors

[GRAPHICS] Owing to the electronic nature of the bridging nitrogen atoms which can adopt different hybridizations and form various conjugations with the adjacent pyridine(s), methylazacalix[4] pyridine underwent conformation and cavity preorganization to highly selectively bind the Zn2+ ion. Rigidification and coplanarity of the macrocyclic ring led to a great enhancement of fluorescence of the intrinsic fluorescent host molecule.