Two hexaazatriphenylene based selective off-on fluorescent chemsensors for cadmium(II)

Two hexaazatriphenylene (HAT) derivatives, 2,3,6,7-tetramethyl-10,11-di(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (1) and 2,3-dimethyl-6,7,10,11-tetra(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (2), were designed and synthesized. Both 1 and 2 exhibited high off-on fluorescent selectivity for Cd(2+) over many other metal ions, and the detection limits were determined to be 0.6 and 5.0 μM, respectively. The stoichiometry and coordination mode of blue fluorescent 1-Cd(2+) and cyan fluorescent 2-Cd(2+) were determined with fluorescence titration fit, Job's plot analysis, (1)H NMR titration and X-ray crystallography, and the fluorescence enhancement mechanism was analyzed with density functional theory calculation.