Fluorescence and colorimetric dual-mode sensing of copper ions and fingerprint visualization by benzimidazole derivatives.

In this paper, the molecular fluorescence probe H containing an imidazole structure was designed and synthesized by forming a ring between two amino groups and one aldehyde group. The synthesized probe H exhibits a Stokes shift of 144 nm with fluorescence emission at 555 nm and excitation at 411 nm. The fluorescence of probe H was quenched by the addition of Cu²⁺ and accompanied a red-shift of ultraviolet-visible (UV-Vis) absorption spectrum. Probe H reveals good selectivity and high sensitivity to Cu²⁺ in the fluorescence and UV-Vis absorption spectrum. And the limit of detection (LOD) for Cu²⁺ by fluorescence and UV-Vis spectrum methods were 0.14 nmol L^-1 and 1.34 μmol L^-1, respectively. The binding ratio of probe H and Cu²⁺ is 1:1 according to the Job's plot equation. High resolution mass spectrometry (HRMS) and density function theory (DFT) calculations proved that the solvent acetonitrile and anionic chloride ion participated in the formation of H-Cu²⁺ complex. Furthermore, the established fluorescence analytical method was successfully applied for the detection of Cu²⁺ and spiked recovery experiments in tap water and mineral water. In addition, the probe exhibited outstanding solid-state fluorescence because of its excellently planar structure, and displayed a secondary fingerprint structure in the application of fingerprint detection.