Studies of Optical Properties of Protonated Polyazomethine Thin Films

Abstract

The poly(p-phenyleneazomethine) (PPI) belongs to alternately conjugated polymers revealing semiconducting properties, thus belonging to the family of organic semiconductors. The architecture of the most conjugated polymers consists of chains of carbon atoms linked by alternate single and double bonds or alternate C=C and B units, where B stands for the benzene (phenyl ring). This is the case for many prototypical conjugated polymers, such as polyacetylene, poly(p-phenylene) and poly(p-phenylene-vinylene). Since the –N–B–N=C– B–C– group is isoelectronic with the –C–B–C=C–B– C– group, the incorporation of nitrogen atoms into the conjugated system leads to another class of conjugated polymers closely related to poly(p-phenylene vinylene)s, namely polyazomethines poly(aromatic-Schiff bases) and polyketanils (polyketimines) [1–5]. Conjugated polyketanils can be considered as simple derivatives of the corresponding polyazomethines in which the hydrogen atom of the azomethine group is replaced by an aryl or alkyl group. Doping of conjugated polymers is a well established way of influencing on important electronic, optoelectronic and mechanical properties of semiconducting polymers. Doping of polyazomethines is realized mainly by acid base chemistry [1], which makes the process complex and difficult to control. The purpose of this work is to study optical properties of protonated PPI thin films and begin on theoretical studies on protonation mechanism of this group of materials, emphasis being put on a role of the counter ion. Our