A conducting charge transfer complex between a sexithienyl radical cation and a Keggin-type heteropolyanion (PMo12O40theta) has been synthesized and characterized. These large inorganic ions confer new properties on polymers to which they are linked, for example, multiple redox exchanges, paramagnetism, electrochromism, and catalytic action. The thiophene hexamer is the best compromise between a long-conjugated system and a processable material, and can be considered a typical poly(thiophene) model, thus allowing a better understanding of the electronic interactions between the conducting polymer poly(3-methylthiophene and the dopant anion PMo12O40theta.