Effect of π–π interaction-induced secondary doping on the gold-like luster of oligo(3-methoxythiophene) cast films

Abstract

We herein investigated the effect of benzene contact treatments on the preparation of solution-cast gold-like lustrous films of doped oligo(3-methoxythiophene) (weight-average degree of polymerization = 21). More specifically, benzene contact treatments involving the addition of benzene and benzene exposure were employed. In the former case, benzene was added to a nitromethane coating solution, and the resulting solution was applied to a glass plate to form a film. Compared with the original film, the resulting film exhibited a higher luster and more intense yellowness when 2.0 wt% benzene was added to the coating solutions. In the latter treatment, the original film was exposed to benzene vapor for ≥30 s, which also caused an increase in luster and yellowness. Such a gold-tone-enhancing effect was not observed upon replacing benzene with hexane. Moreover, both benzene contact treatments increased the number of edge-on lamellar crystallites in the film. Based on these results, it was concluded that upon benzene contact treatment, the oligomers adopt a planar conformation in which benzene molecules are sandwiched between the oligomers. These sandwich structures facilitate the formation of edge-on lamellar crystallites, which are the most likely cause of the gold tone. Solution-cast gold-like lustrous films of oligo(3-methoxythiophene) were subjected to benzene exposure and benzene addition treatments. Both treatments provided films with a higher luster and more intense yellowness, i.e., an enhancement in a gold tone. Such a gold-tone-enhancing effect was explained by a model in which upon the treatments, the oligomers adopt a planar conformation through π–π interactions between benzene and the thiophene rings, and the resulting sandwich structures facilitate the formation of edge-on lamellar crystallites, the most likely gold-tone developing structure.