A luminescent sensor responsive to common oxoacids: X-ray crystal structure of [H₃O·1,8-Oxybis(ethyleneoxyethyleneoxy)anthracene-9,10-dione] ClO₄

1,8-Oxybis(ethyleneoxyethyleneoxy)anthracene-9,10-dione with a reduced cavity size, due to the presence of a carbonyl oxygen within the crown, has been shown by X-ray crystallography to encapsulate a hydronium ion. Hydrogen bonds between the hydronium ion and the crown oxygens are particularly strong, averaging 2.56 Å. The polyether ring also exhibits a pronounced folding to optimize encapsulation of the hydronium ion. The hydronium hydrogen atoms have been unequivocally observed, indicating near ideal pyramidal geometry, due to the absence of hydrogen-bonding disorders previously observed in other [H₃O·18-crown-6]⁺ structure analyses. Intense luminescence is concurrently observed with complexation of the hydronium ion within the polyether ring. Common oxoacids acids, such as HNO₃, H₂SO₄, HClO₄, and CF₃SO₃H, result in luminescent intensities approximately 40 times larger than that of 1,8-oxybis(ethyleneoxyethyleneoxy)anthracene-9,10- dione alone, which also correlates with the pK(a)s of these acids. This capability serves a unique pK(a) regimen as a possible sensor molecule for measuring acidities of potent oxo and superacids.