Ionic Stabilization of the Polythiophene-Oxygen Charge-Transfer Complex

A substantial reduction in the rate of irreversible polymer photo oxidation was observed through the ionic stabilization of the polymer-O-2 charge transfer complex (CTC) in amorphous polythiophene thin films. Through the incorporation of anionic functionality containing mobile cations, it was found that CTC stability increases with increasing cation charge density. This results in an increased rate of electron transfer to molecular oxygen relative to photosensitization and reaction of O-I(2), leading to a reduction in the overall rate of polymer degradation. UV-vis and FTIR spectroscopy were utilized to determine the identity of intermediate and irreversible photodegradation products as well as the effect of ion identity on the dominant photo-oxidation mechanism. As polymer-O-2 CTCs are common in the photo-oxidation of many conjugated polymers, these results have significant implications for the ongoing effort to produce commercially viable organic electronic and photonic devices.