A high-performance fluorescent and ratiometric colorimetric detection of Cu²⁺ in practice

To monitor Cu²⁺ efficiently, a kind of D-π-A-π-D conjugated 3,5-di-(2-hydroxyl naphthaldehyde)-iminyl triazole (HNIT) was developed, using triazole as the electron acceptor, 2-hydroxyl naphthaline as the electron donor, and -CN- as the bridging group. The proposed HNIT possessed superior UV-vis and fluorescent spectral property with high molar absorption coefficient of 2.313 × 10⁴ L mol^-1 cm^-1 and fluorescence quantum yield of 36.2%. Trace Cu²⁺ could exclusively alter its UV-vis and fluorescent property with clear color change. Under the optimized conditions, a high-performance fluorescent and ratiometric colorimetric detection of Cu²⁺ based on HNIT was efficient, with low detection limits of 3.3 × 10^-8 mol L^-1 (S/N = 3) and 9.6 × 10^-8 mol L^-1 (S/N = 3), respectively. It well satisfied with the safe value of 31.5 μM Cu²⁺ in drinking water recommended by World Health Organization (WHO). When applied for detection of Cu²⁺ in real environmental samples, the recovery was in the range of 97.5-105.2%. The recognition mechanism for HNIT to Cu²⁺ realized quite stable 6-membered rings between electron-deficient Cu²⁺ and electron-rich N and O atoms in HNIT with 1 : 2 chemical stoichiometry of HNIT to Cu²⁺.