Solid-state emissive metallo-supramolecular assemblies of quinoline-based acyl hydrazone

Development of fluorescence-based sensory materials for metal elements is currently in the mainstream of research due to the simplicity and usability of fluorescence as a method of detection. Herein, we report a novel “bis”-quinoline-based acyl hydrazone—named bQH that could be synthesized by a facile, low-cost method through simple condensation of hydrazide with an aldehyde. This acyl hydrazone showed emissive properties through Zn selective binding, especially in its solid-state, as shown by experiments such as UV–Vis, photoluminescence (PL), nuclear magnetic resonance (NMR), and inductively-coupled plasma-optical emission spectroscopies (ICP-OES), and energy-dispersive X-ray spectroscopy (EDS) mapping. The binding modes in which bQH coordinates to Zn²⁺ was proved to consist of two modes, 1:1 and 1:2 (bQH:Zn²⁺), where the binding mode was controlled by the Zn²⁺ ion content. Under the 1:1 binding mode, bQH-Zn²⁺ complexes formed a polymeric array through the metallo-supramolecular assembly. The resulting bQH-Zn²⁺ complex maintained its fluorescence in solid-state and exhibited excellent fluorescence intensity as compared to the previously reported quinoline-based acyl hydrazone derivative (mQH).