Luminescence and Structural Comparisons of Strong-Acid Sensor Molecules. 2

Anthraquinone-containing cyclic polyether hosts form 1:1 complexes with hydronium ion, producing large enhancements in luminescence via inversion of npi* and pipi* exited states. We have characterized the binding of hydronium ion within these host molecules and have synthesized a large variety of analogous hosts that contain different structural and electronic features that allow better understanding of what controls binding and luminescence capacity in this class of fluorescent sensor molecules. X-ray crystallography of an anthraquinone host that contains terminal amine functional groups rather than terminal ether groups is investigated, and complete proton transfer to carbonyl groups is observed in concentrated sulfuric acid media that also produces a previously unobserved luminescence.