Study on the interaction between nitroxide free radical and conjugated polyelectrolytes by fluorimetry

Area of Science:

• Photophysics
• Polymer Chemistry
• Supramolecular Chemistry

Background:

• Conjugated polyelectrolytes exhibit fluorescence sensitive to their environment.
• Paramagnetic species like TEMPO are known to quench fluorescence.
• Understanding quenching mechanisms is crucial for developing optical sensors.

Purpose of the Study:

• To investigate the fluorescence quenching of PPE-SO(3) by TEMPO in aqueous solution.
• To analyze the Stern-Volmer relationship at varying TEMPO concentrations.
• To study the recovery of fluorescence and kinetics upon reduction of TEMPO.

Main Methods:

• Fluorescence spectroscopy to monitor PPE-SO(3) emission.
• Titration with TEMPO to determine quenching constants.
• Addition of ascorbic acid to induce fluorescence recovery.
• Kinetic analysis of fluorescence rise under pseudo-first-order conditions.

Main Results:

• Stern-Volmer quenching constant (K_SV) of 94 mol/L at low TEMPO concentration.
• Superlinear Stern-Volmer plots observed at higher quencher concentrations.
• Complete fluorescence recovery of PPE-SO(3) upon TEMPO reduction by ascorbic acid.
• Pseudo-first-order kinetics for fluorescence recovery with a second-order rate constant of 0.7 mol/L/s.

Conclusions:

• TEMPO effectively quenches PPE-SO(3) fluorescence in water.
• The quenching mechanism exhibits concentration-dependent deviations from linearity.
• Ascorbic acid efficiently reverses quenching, allowing for kinetic studies.
• The determined rate constants provide insights into the interaction dynamics.