Anion binding by fluorescent biimidazole diamides.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Imidazole derivatives are versatile scaffolds in medicinal chemistry and materials science.
• Developing selective anion sensors is crucial for environmental monitoring and biological studies.
• Biimidazole structures offer unique hydrogen bonding and coordination capabilities.

Purpose of the Study:

• To synthesize novel 2,2'-biimidazole derivatives with varying amide functionalities.
• To investigate the solid-state structure and intermolecular interactions of these biimidazoles.
• To evaluate the anion binding properties and selectivity of the synthesized compounds.

Main Methods:

• Synthesis of six 2,2'-biimidazoles via palladium(0)-catalyzed homocoupling of 2-iodoimidazoles.
• X-ray diffraction analysis to determine solid-state structures.
• Spectroscopic studies (UV-Vis absorption, fluorescence emission, 1H NMR) to assess anion binding.
• Determination of binding constants (Kassoc) for anion complexation.

Main Results:

• Successful synthesis of six biimidazole derivatives.
• X-ray diffraction revealed coplanar imidazole rings, anti-amide arrangements, and significant hydrogen bonding networks.
• Fluorescence quenching observed upon addition of dihydrogenphosphate and chloride anions in dichloromethane.
• High binding constants (Kassoc ~ 10^4 M^-1) for H2PO4- and Cl-.
• One derivative demonstrated selectivity for chloride ions.
• 1H NMR confirmed the involvement of amide NH groups in anion binding.

Conclusions:

• The synthesized biimidazoles exhibit well-defined solid-state structures with extensive hydrogen bonding.
• These compounds function as effective receptors for dihydrogenphosphate and chloride anions.
• The observed fluorescence quenching and binding constants highlight their potential as anion sensors.
• Structural modifications can lead to selective anion recognition, as demonstrated by the chloride-selective receptor.