C2-symmetrical hexaazatriphenylene derivatives as colorimetric and ratiometric fluorescence chemsensors for Zn2+

Two C2-symmetrical hexaazatriphenylene (HAT) derivatives, 2,3-diphenyl-6,7,10,11-tetra(pyridin-2-yl)dipyrazino[2,3-f:2′,3′-h]quinoxaline (1) and 2,3,6,7-tetraphenyl-10,11-di(pyridin-2-yl)dipyrazino[2,3-f:2′,3′-h]quinoxaline (2), were designed and synthesized by the condensation reaction of 1,2-diamines and 1,2-diketones. Both compounds 1 and 2 exhibit sensitive, ratiometric and colorimetric fluorescence selectivity for Zn2+ ion over alkali ions, alkaline earth ions and a wide range of transition metal ions upon excitation at 350 nm in acetonitrile/water. The interactions between 1 or 2 and Zn2+ can be observed by naked eyes with an obvious color change of the solution from colorless to yellow. For fluorescence intensity of 2 toward Zn2+, a good linearity (correlation coefficient R2=0.993) was established with a detection limit of 0.095 μM, which is more sensitive than that of 1 (0.2 μM). The binding modes of the free ligands 1 and 2 with Zn2+ are discussed in context to their photophysical and electrochemical properties as well as single X-ray crystallographic structures of 1, 2 and 1-Zn.