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 V_oc values of 0.67–0.71 V, J_sc 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.