Zinc(ii) ion detection and fluorescence emission properties of a diaminomaleonitrile-derived unsymmetrical Schiff base ligand.

A novel Schiff base ligand, 2-amino-3-((()-2,5-dihydroxybenzylidene)amino)maleonitrile hemihydrate (CHNO·½HO or HL), was synthesized by a condensation reaction of diaminomaleonitrile and 2,5-dihydroxybenzaldehyde in ethanol. Its crystal structure, fluorescence (FL) emission and Zn(ii)-detection properties were studied. The crystal structure of HL belongs to a face-centered orthorhombic space group (2), confirming its crystalline nature. HL emitted green-colored fluorescence in MeCN, EtOH, and DMF, with varying FL yields of 0.53, 0.68, and 0.95, respectively. This suggests that the solvent environment plays a crucial role in modulating the FL properties of HL. In DMF, the gradual addition of Zn(ii) to the HL solution resulted in a color change from yellow to orange, accompanied by the appearance of new absorbance bands at 494 nm and two isosbestic points at 300 and 440 nm. These phenomena were not observed either in MeCN or EtOH, indicating that Zn(ii)-HL binding was more pronounced in DMF. Thus, HL demonstrated sensitive Zn(ii) binding, with a 1 : 1 binding stoichiometry, a high binding constant (3.745 × 10 μM), and a low limit of detection (3.455 × 10 μM). Overall, the findings highlight the potential of the novel crystalline HL for efficient FL emission and sensitive Zn(ii) detection in DMF, suggesting its potential utilization for fabricating light-emitting organic devices and metal-ion sensors.