An introduction of 8-Hydroxyquinoline

8-Hydroxquinoline(8-HQ), one of the most popular and versatile organic compound, is an organic crystalline material that made up of two rings: a phenol ring fused with pyridine ring. 8-Hydroxyquinoline and its derivatives have found a great variety of applications ranging from pharmacological and pharmaceutical agents to electron carriers in organic light-emitting diodes (OLEDs) and fluorescent chemosensors for metal ions. In medicinal field, 8-hydroxyquinoline derivatives can be used as insecticides, antibacterial, fungicidal, neuroprotective, and anti-HIV agents. In addition, due to their chelating ability toward a great number of metal cations, derivatives of 8-HQ have found many applications in fluorescent sensing of biological and environmentally important metal ions such as Al³⁺ and Zn²⁺.8-hydroxyquinoline ligand has been applied for analytical purposes and separation techniques, it is an excellent reagent for gravimetric analysis and it can be used for extraction of metal ions. As it is well known that 8-hydroxyquinoline is weakly fluorescent because of the excited state intermolecular proton transfer of the proton of the OH-function to the nitrogen of the pyridine moiety; chelating metals ions react with 8-hydroxyquinoline to increase the fluorescence emission of this ligand greatly. This increase in the emission appears to be largely a result of the increased rigidity in the molecule.This article will focus on the structural, physical properties and chemical properties aspects of 8-HQ derivatives and their metal complexes. Furthermore, particular attention is paid to the applications of 8-HQ derivatives in various fields.