pH-dependent optical properties of a poly(phenylene ethynylene) conjugated polyampholyte.

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Electronics

Background:

• Conjugated polymers offer tunable electronic and optical properties.
• pH-responsive polymers are crucial for sensing and drug delivery applications.
• Poly(phenylene ethynylene)s (PPEs) are a versatile class of conjugated polymers.

Purpose of the Study:

• To synthesize and characterize a novel PPE-based polymer with both cationic and anionic groups.
• To investigate the pH-induced transition of the polymer from a polycation to a polyampholyte.
• To explore the impact of this transition on the polymer's optical properties and fluorescence quenching behavior.

Main Methods:

• Sonogashira coupling for polymer synthesis.
• UV-Vis absorption and fluorescence spectroscopy to study optical properties.
• Stern-Volmer fluorescence quenching experiments with a negatively charged quencher (NDS).

Main Results:

• Successful synthesis of PPE-NMe(3)(+)-COO(-) containing tetraalkylammonium and carboxylate groups.
• Demonstration of a pH-induced transition from cationic polyelectrolyte to polyampholyte.
• Observed changes in absorption oscillator strength and fluorescence quantum efficiency linked to the pH transition.
• Enhanced fluorescence quenching at low pH (polycation) compared to high pH (polyampholyte) with NDS.

Conclusions:

• The synthesized polymer exhibits tunable optical properties based on pH.
• The pH-dependent transition significantly influences fluorescence quenching efficiency.
• This polymer shows potential for pH-sensitive applications, such as fluorescent sensors.