Microwave Synthesis of Thionated Naphthalene Diimide-Based Small Molecules and Polymers

Thionated naphthalene diimides (NDIs) are promising materials for n-type organic semiconductors; despite their potential, synthetic routes to thionated NDIs are generally lengthy, nonselective, and low yielding and their polymeric analogues have yet to be reported in the literature. Here, we describe the rapid and selective thionation of thiophene- and selenophene-flanked NDIs using microwave irradiation and excess Lawesson's reagent. Remarkably, >99% conversion to the trans-dithionated product is observed by NMR within 45 min. Steric effects imparted by NDI core substituents prevent excess thionation, simplifying purification procedures. We apply this methodology to the postpolymerization thionation of NDI-based polymers to afford a series of polymers with varying degrees of thionation. Thionated NDIs exhibit bathochromic shifts of up to ∼100 nm in localized absorption maxima and increased electron affinities.