4-(2,2′-Bipyridine-5-yl)benzaldehyde as a novel fluorescent reagent for Zn2+ with emission in the near-infrared region

4-(2,2′-Bipyridine-5-yl)benzaldehyde, compound 1, was designed and readily synthesized as a novel fluorescent reagent for Zn2+ with emission in the near-infrared region. Upon addition of Zn2+, the fluorescent reagent showed significant changes in both absorption and fluorescence spectra, in particular, a marked enhancement in the fluorescent intensity in the near-infrared region. By contrast, most of other metal ions caused only marginal variations in the optical properties of the fluorescent reagent. The job plot indicates that the fluorescent reagent forms a 1:1 complex with Zn2+. The binding constant was calculated to be 4.57 × 104 M−1. Furthermore, the fluorescent reagent was employed to measure the Zn2+ concentrations in real water samples with good accuracy.