Fluorescent Calixarene Scaffolds for NO Detection in Protic Media

We present the first fluorescent water-soluble conjugated calixarene scaffolds that are capable of NO gas detection. Two different scaffolds, one based on a 5,5'-bicalixarene structure and its isomer bearing two distantly conjugated calixarene moieties, were synthesized. While the fluorescence of both isomers is quenched upon either passing of NO gas or generating it in situ from diethylamine NONOate, the bicalixarene-based scaffold showed a significantly stronger response. We also present an example of a dye encapsulation strategy to achieve the detection of NO at longer wavelengths than in the parent calixarene host. Finally, a conjugated polymer bearing a 5,5'-bicalixarene scaffold has also been prepared and demonstrated enhanced sensitivity compared to the monomer due to the molecular wire effect.