Conjugated Polyelectrolyte-Based Fluorescent Surfactants: Synthesis and Emulsion Formation

Visualization of the amphiphilic interface through fluorescence is of importance to understand the interfacial phenomena in a non-invasive way. However, there is a scarcity of surfactant conjugated polymers with strong fluorescence owing to the difficulty of synthetic procedures employing a hydrophobic polymer backbone with strongly hydrophilic side-chains. Herein, we report novel fluorescent polymeric surfactants based on conjugated polyelectrolytes (CPEs) containing zwitterionic and alkyl side-chains. A fluorescent poly(phenylene ethynylene) (PPE) backbone with amine and alkyl groups was synthesized by Sonogashira-type polymerization. The amines on PPE were treated with 1,3-propanesultone, resulting in the formation of zwitterionic groups. Stable oil-in-water emulsion was successfully formed with co-surfactants. The conformations of polymers in different physical states were compared through photophysical analysis. It was found that the PPE backbone was highly planarized at the oil-water interface with extended pi-pi interactions, providing potential applications in the non-invasive visualization of amphiphilic interfaces found in colloids and biology.