pH Switchable Electrochemical and Optical Properties of Polyoctylthiophene – Pyrene Composites

Polyoctylthiophene electrochemical and optical properties are dependent on the polymer oxidation state, generally requiring presence of doping ions. In this work polyoctylthiophene composites with pyrene or aminopyrene have been prepared and studied using optical and electrochemical methods. It is shown that in the composite formed pyrene molecules act as molecular dopant for the conducting polymer, resulting in a system of partially oxidized polythiophene backbone, yet of high lipophilicity. On the other hand, composite of aminopyrene with polyoctylthiophene is characterized with pH dependent electrochemical and optical properties. The difference arises mostly from the protonation/ deprotonation reaction occurring for aminopyrene embedded in polyoctylothiophene. Nanoparticles of polythiophene-aminopyrene show turn-on emission dependence on increase of hydrogen ions concentration in solution in a wide pH range from 12 to 5. For low pH high emission activity is observed for nanoparticles, whereas for films high lipophilicity and low electrochemical activity pointing to presence of semiconducting polymer in the system for protonated aminopyrene. For high pH, when deprotonation of aminopyrene is observed, the system is characterized with low optical, yet high electrochemical activity and low lipophilicity. The electrochemical activity of polyoctylthiophene-aminopyrene composite can be reversibly switched simply by solution pH change.