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-pi-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.