pH-Dependent Optical Properties of a Poly(phenylene ethynylene) Conjugated Polyampholyte

• Published in: Langmuir Vol. 27; no. 5; pp. 1565 - 1568
• Main Authors: Ji, Eunkyung, Whitten, David G, Schanze, Kirk S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.03.2011
• Subjects: Absorption; Carboxylic Acids - chemistry; Chemistry; Exact sciences and technology; General and physical chemistry; Hydrogen-Ion Concentration; Optical Phenomena; Polymers - chemistry; Quaternary Ammonium Compounds - chemistry; Solutions; Spectrometry, Fluorescence; Polyampholyte; Basic solution; Phenylene polymer; Fluorescence; Polymer; Polyelectrolyte; Polycation; Carboxylic acid; Efficiency; Optical properties; Carboxylate; pH; Deprotonation
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la104586t

A poly(phenylene ethynylene) conjugated polymer (PPE-NMe3 +-COO−) containing tetraalkylammonium groups and carboxylate groups has been synthesized by Sonogashira coupling. Due to the presence of the strong cationic and weak anionic pendant units, the polymer undergoes a pH-induced transition from cationic polyelectrolyte to polyampholyte due to deprotonation of the carboxylic acid units in basic solution. Studies of the pH dependence of the polymers’ optical properties reveal changes in absorption oscillator strength and fluorescence quantum efficiency that are triggered by the transition from cationic polyelectrolyte to polyampholyte nature. Stern−Volmer fluorescence quenching of PPE-NMe3 +-COO− with a negatively charged quencher 1,4,5,8-naphthalenediimide-N,N-bis(methylsulfonate) (NDS) shows that the polymer fluorescence quenching is amplified at low pH where the polymer is a polycation, whereas the quenching efficiency is considerably less at high pH.