Pd-Free synthesis of dithienothiophene-based oligoaryls for effective hole-transporting materials by optimized Cu-catalyzed annulation and direct C-H arylation

Dithienothiophene (DTT), a versatile building block for π-conjugated organic materials, has been efficiently synthesized through copper-catalysis with an inexpensive sulfur source in the essential ring-closure/C-S bond formation step, instead of using previously often reported n-butyllithium, costly bis(phenylsulfonyl)sulfide, or palladium-based catalysis. Furthermore, π-extension from DTT was also achieved step-economically by optimized copper-catalyzed direct C-H arylation reactions, giving three new oligoaryls that were used as effective hole-transporting materials (HTMs) in perovskite solar cells. One of the solar devices demonstrated the highest energy conversion efficiency of 14.67%. For the first time, [Cu]-catalyzed direct C-H/C-I couplings were used as key transformations to access small molecular HTMs.