Ionic liquids are composed of cations and anions with specific volumes. In general, cations have a larger volume and anions have a smaller volume. Compared with traditional solid and liquid materials, ionic liquids have many unique physical and chemical properties, including low volatility, high stability, wide electrochemical stability window and others. Moreover, as a kind of green solvent, ionic liquid plays an increasingly important role in chemical synthesis and physical extraction. Furthermore, ionic liquids are highly designable. In order to enrich the function of ionic liquids, fluorescent groups can be introduced into the ionic liquids to prepare fluorescent ionic liquids. Fluorescent ionic liquid is a kind of functional ionic liquid, which not only has the characteristics of ionic liquid, but also has strong fluorescence performance due to the introduction of fluorescent groups into it. In addition, fluorescent ionic liquids are ideal fluorescent materials because of their good fluorescence properties and high quantum yield. The general structure of fluorescent ionic liquid is shown in Figure 1.
Figure 1. The general structure of fluorescent ionic liquid.
Using the fluorescence properties of fluorescent ionic liquids, they can be widely used in fluorescent labeling, fluorescent probes, fluorescence imaging and others.
- Fluorescent labeling: Fluorescent ionic liquids have been widely used in protein functional research, drug screening and others by virtue of their fluorescence imaging function. Fluorescent ionic liquids can be used to detect the activity of target protein, which is already applied to the drug screening and drug development of target protein for disease therapy. For example, a group has reported that fluorescent labeling of proteins can be achieved using benzimidazole-type fluorescent ionic liquids.
- Fluorescent probe: By designing the structure of the fluorescent ionic liquid, it can be used as a fluorescent probe for qualitative or quantitative analysis of metal ions. For example, mercury in the environment can enter the human body through food and drinking water and seriously harm human health. It has become one of the most concerned environmental pollutants in the world. A research group has designed and synthesized a new water-soluble fluorescent ionic liquid. The fluorescence intensity of this fluorescent ionic liquid can be enhanced after the interaction with Hg2+. The increased fluorescence intensity has a linear relationship with mercury concentration in a certain range. Based on this, a fluorescent probe for the determination of trace mercury in water can be established.
Figure 2. An example of fluorescent ionic liquid used as fluorescent probe.
- Fluorescence imaging: Fluorescent ionic liquids can be used in the field of fluorescence imaging with high sensitivity, good repeatability and rich information. The application of this technology in the early detection of some diseases, such as cancer, plays an important role in the pathogenesis research and early treatment.
- Others: In addition to the above fields, fluorescent ionic liquids have been widely used in other fields. For example, introducing ligands into fluorescent ionic liquids can be used as coating materials. Moreover, fluorescent ionic liquid with polymer can be used as catalyst for the separation of metal ions and gas. In addition, fluorescent ionic liquid can also be used as modifier to functionalize carbon nanotubes.
Depending on the type of fluorophore, fluorescent ionic liquids can be classified as anthracene, naphthalene rings, benzimidazole, pyrene, perylene imide, and others.
- Li Q, Peng K, Lu Y, et al. Synthesis of fluorescent ionic liquid-functionalized silicon nanoparticles with tunable amphiphilicity and selective determination of Hg2+[J]. Journal of Materials Chemistry B, 2018, 6(48):8214-8220.