The Optimization of Direct Heteroarylation and Sonogashira Cross-Coupling Reactions as Efficient and Sustainable Synthetic Methods To Access π‑Conjugated Materials with Near-Infrared Absorption

Two π-conjugated thienoisoindigo-based organic small molecules have been designed to be synthetically accessible through sustainable direct heteroarylation or Sonogashira C–C bond forming cross-coupling reactions utilizing a heterogeneous palladium catalyst. To access these materials, one molecule, TII-ThNaph2, contains a thiophene π-bridge to facilitate direct heteroarylation protocols, whereas the other, TII-AcNaph2, contains an acetylene π-bridge required for Sonogashira couplings. The synthetic route to both final materials was optimized to investigate the reactivity of thienoisoindigo, which to this point has not been significantly explored in comparison to other popular organic dyes such as diketopyrrolopyrrole and isoindigo. Considering the reported interest of thienoisoindigo-based materials in organic solar cells and field-effect transistors, both final materials have been characterized for their optical, electrochemical and thermal properties offering a comparison of the structure–property relationships that manifest as a result of the two different π-bridging units.