A concave fluorescent sensor for anions based on 6-methoxy-1-methylquinolinium

Area of Science:

• Supramolecular Chemistry
• Analytical Chemistry
• Fluorescence Spectroscopy

Background:

• Development of selective chemosensors for anions is crucial in various scientific fields.
• Existing sensors often lack the required sensitivity or selectivity for practical applications.
• Fluorogenic quinolinium derivatives offer potential for sensitive anion detection.

Purpose of the Study:

• To synthesize and characterize a novel multivalent fluorogenic ligand (ligand 2) for anion recognition.
• To investigate the binding interactions between ligand 2 and various inorganic anions.
• To evaluate the sensitivity and selectivity of ligand 2 as a fluorescent sensor for anions.

Main Methods:

• Synthesis of the multivalent ligand 2 featuring three 6-methoxy-1-methylquinolinium fragments on a mesityl platform.
• Spectroscopic studies including 1H NMR to elucidate binding modes.
• Molecular modeling to understand the host-guest interactions and cavity formation.
• Fluorimetric titrations to quantify anion binding and quenching efficiency.

Main Results:

• Ligand 2 forms 1:1 adducts with halides and other inorganic anions in acetonitrile.
• 1H NMR and molecular modeling confirmed a cavity for anion inclusion and electrostatic interactions.
• Anion binding induced fluorescence quenching, with efficiency following the order Br(-)>>I(-)>NCS(-)>>Cl(-)>NO(3) (-)>HSO(4) (-).
• The fluorimetric response of ligand 2 was orders of magnitude more sensitive than the monomeric analog (ligand 1).

Conclusions:

• Ligand 2 is a highly effective and sensitive fluorescent sensor for inorganic anions.
• The multivalent design enhances binding affinity and signal transduction compared to monomeric units.
• This work provides a promising platform for developing advanced anion sensing technologies.