Dithienophosphole-based molecular electron acceptors constructed using direct (hetero)arylation cross-coupling methods

Abstract

Herein we report on the first successful coupling of the dithienophosphole (S₂PO) functional building block with three types of heteroaryl end caps using direct (hetero)arylation C–H bond functionalization methods. As a model reaction, S₂PO was coupled with ethylhexyl phthalimide. The reaction conditions were optimized to give yields up to 67%. Applying the optimized conditions to hexyl phthalimide and N-annulated perylene diimide gave yields of 68% and 49% for the corresponding products, respectively. Compounds were characterized by optical absorption and emission spectroscopy, cyclic voltammetry, differential scanning calorimetry, and thermal gravimetric analysis and compared with their phosphole-free analogues. It was found that incorporation of the phosphole resulted in a lowering of the LUMO energy level for both compounds compared to their analogues. The bis(perylene diimide)S₂PO product was used as an acceptor in bulk heterojunction organic photovoltaic devices with three donor polymers. High V_oc values of 1.0–1.1 V were obtained from devices spin cast from o-dichlorobenzene, a significant result for devices with non-fullerene acceptors.