Optical-structural correlation in a novel quinoxaline-based anion sensor

Protonation of 2,3-dipyridin-2-ylquinoxaline 1 results in a significant change in the conformation of the molecule as revealed by H-1 NMR and optical spectroscopies and by single crystal X-ray diffraction studies performed upon the product, 2-(3-pyridin-2-ylquinoxalin-2-yl)pyridinium hexafluorophosphate, 2. A further consequence of protonation is that the electronic properties of 2 are altered in such a way as to produce a luminescent compound, the luminescence of which is quenched by a variety of biologically and commercially relevant anions.