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 [H 3 O·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 HNO 3, H 2 SO 4, HClO 4, and CF 3 SO 3 H, 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 p K a s of these acids. This capability serves a unique p K a regimen as a possible sensor molecule for measuring acidities of potent oxo and superacids.