A New, General Approach to Tuning the Properties of Functionalized Polythiophenes:  The Oxidative Polymerization of Monosubstituted Bithiophenes

A new synthetic approach to functionalized polythiophenes utilizing 4-substituted 2,2‘-bithiophenes is described. The general utility of this approach is illustrated by the preparation of the representative poly(4-substituted 2,2‘-bithiophenes) (where substituent = octyl, hydroxymethyl, carboxy, carbomethoxy, or acetoxyethyl). The use of monofunctionalized bithiophenes as monomers has a number of advantages over traditional 3-substituted thiophene precursors. These advantages include direct oxidative polymerization of electron-poor monomers, selective oxidative polymerization in the presence of oxidatively sensitive side chains, polymerization without oxidative degradation of the backbone, and production of polymers with decreased side-chain density. The combination of these advantages allows the facile oxidative polymerization of monomers containing a large variety of functional groups. The reduction in side-chain density results in polymers with increased effective conjugation lengths as evidenced by their improved electrical and optical properties.