A fluorescent copper(II) complex based on 4,4-oxybisbenzoic acid and benzimidazole for selective detection of nitroaromatic compounds

Abstract

Nitroaromatic compounds (NACs) are electron-deficient aromatic molecules extensively used in explosives, dyes, and pesticides, and their high toxicity and environmental persistence pose serious risks to human health and ecological systems. Consequently, the development of sensitive, selective, and portable sensing platforms for NAC detection is of significant importance. In this work, a copper-based coordination complex, [Cu(Oba)2(Beim)(H2O)] (1) (H2Oba = 4,4’-oxybisbenzoic acid; Beim = benzimidazole), was synthesized via a conventional method and fully characterized using standard instrumental techniques. Infrared spectroscopy confirmed the coordination environment, with characteristic bands observed at 1666 cm-1 (vC = O), 1243 cm-1 (vC - - N), and 3061 cm-1 (vN --H). The complex exhibits strong fluorescence emission at 490 nm and good thermal stability. Fluorescence sensing studies revealed a significant quenching response in the presence of NACs, particularly 4-nitroaniline. The sensor demonstrated a low limit of detection (LOD) of 1.46 ppm and a high Stern–Volmer quenching constant (KSV = 9.16 × 104 M-1) towards 4-nitroaniline, indicating excellent sensitivity and selectivity. Furthermore, recyclability experiments showed that the complex could be reused for up to four sensing cycles without significant loss of performance. These results highlight the potential of the copper coordination complex as an efficient and reusable fluorescent sensor for nitroaromatic compounds.