Low band gap materials play a critical role in organic photovoltaics and organic photosensors. Although initial approaches to low band gap materials utilized fused-ring thiophenes that enhance the quinoidal nature of the backbone, the most commonly applied approach to the production of low band gap conjugated materials is through the utilization of a 'donor-acceptor' framework. This 'donor-acceptor' (D-A) approach to low band gap materials was first introduced in 1992 by Havinga and coworkers, in which it was proposed that materials with alternating electron-rich (donor) and electron-deficient (acceptor) moieties along the same backbone could result in a hybrid material with HOMO levels characteristic of the donor and LUMO levels characteristic of the acceptor. This approach has since become a critical design factor in the generation of low (Eg < 1.5 eV) and reduced (Eg = 1.5-2.0 eV) band gap materials.
A class of such D-A materials have utilized thieno[3,4-b]pyrazines (TPs) and its analogues as 'acceptors' within D-A frameworks, resulting in the successful generation of low and reduced band gap materials. Recent reports, however, have revealed that TPs act simultaneously as both strong 'acceptors' and strong 'donors', with donor abilities comparable with 3,4-ethylenedioxythiophene (EDOT). As such, the TP unit contains an internal D-A interaction that dominate the electronics of TP-based materials. Effects of the ambipolar nature of TP on its materials will be presented along with the potential of utilizing TP as a donor in D-A frameworks to produce new nontraditional materials.