Synthesis of a novel hexaazatriphenylene derivative for the selective detection of copper ions in aqueous solution

A hexaazatriphenylene (HAT) derivative, naphtho[2,3-h]naphtho[2',3':7,8]quinoxalino[2,3-a]naphtho[2',3':7,8]quinoxalino[2,3-c]phenazine-5,10,15,20,25,30-hexaone (NQH) was synthesized, characterized, and found to have novel properties in being selective toward the detection of copper (Cu²⁺) ions. The capability of NQH to be employed as a colorimetric, chemo-fluorescence and electrochemical sensor for the detection of Cu²⁺ was demonstrated by performing UV-Vis absorbance, fluorescence intensity, and cyclic voltammetry (CV) measurements. The interaction between NQH and Cu²⁺ was initially observed with an obvious color change from yellow to brown upon the addition of Cu²⁺ ions to NQH. The interaction was also confirmed by UV-Vis absorbance, fluorescence intensity, and mass spectroscopy (MS/MS) measurements. UV absorbance, fluorescence and CV of NQH toward Cu²⁺ showed good linearity with a detection limit of 3.32 μM, 2.20 μM and 0.78 μM, respectively, which are lower than the toxicity levels of copper in drinking water (20-30 μM) set by the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO). A 1 : 2 stoichiometry complexation between NQH and Cu²⁺ was confirmed by Job's plot and MS/MS. In addition, the selectivity and sensitivity of the NQH compound towards Cu²⁺ ions were further confirmed by performing CV on a screen printed flexible and planar electrochemical sensor.