Synthesis of largely π-extended naphthalenediimides via C–H activation towards highly soluble and narrow band-gap organic optoelectronic materials

Atom-economic coupling reactions based on C–H activation are generally used to synthesize small conjugated systems, but their applications in constructing largely π-conjugated systems have been rarely reported. Herein, we report the preparation of largely π-extended naphthalenediimides (4a–c, with molecular weights of up to 2800) by using efficient palladium-catalyzed C–H/C–H homocouplings, with the yields of up to 94%. The physicochemical properties of 4a–c were studied and they exhibited excellent solubility, thermal stability, quasi-reversible reduction processes, broad and long-wavelength optical absorptions with thin-film optical gaps <1.4 eV and fine-tuned deep LUMO energies (<−4.2 eV), which together with ambient stable electron-transporting behaviors demonstrate their promising applications in optoelectronic devices.