End‐Capping Groups for Small‐Molecule Organic Semiconducting Materials: Synthetic Investigation and Photovoltaic Applications through Direct C–H (Hetero)arylation

A Pd‐catalyzed C–H (hetero)arylation methodology has been optimized for the efficient synthesis of various useful end‐capping groups that are widely applied in small‐molecule optoelectronic materials. We report herein the synthesis of a broad scope of target molecules ranging from donor‐type through acceptor‐type to hybrid‐type end‐capping groups. To demonstrate their application in dye‐sensitized solar cells, we have designed two new D–A–π–A′‐type organic sensitizers (CYL‐3 and CYL‐4), which were synthesized in a step‐economic manner by sequential C–H arylations using the facilely obtained end‐capping groups. The devices based on CYL‐3 and CYL‐4 give Voc values of 0.67–0.71 V, Jsc values of 10.07–11.63 mA cm–2, and FF values of 70.6–72.9 %, which correspond to overall power conversion efficiencies of 4.76–6.02 %. This work is expected to become a practical synthetic alternative allowing materials scientists to access small‐molecule organic materials in fewer synthetic transformations.