Fluorescent chemosensors based on a new type of lower rim-dansylated and bridge-substituted calix[4]arenes

The synthesis, structural and chemosensing properties of several lower rim-dansylated calix4]arenes bearing different methylene bridge substituents are described. Compared to bridge-unsubstituted pendants neither the conformational nor the fluorescence characteristics of the calixarene core are perceptibly influenced by the bridge substituent. X-ray structure as well as NMR measurements indicates the lower rim-propoxylated and-dansylated calixarenes to adopt the cone conformation capable of the complexation of Cu²⁺ ions at micromolar level. Fluorescent measurements point to selective 1:2 calixarene: Cu²⁺ complex formation with sensing parameters being of a suitable level to make the use as a potentially immobilisable chemosensor for the detection of Cu²⁺ ions promising.