From Step-Saving New Synthesis to Photovoltaic Applications of Triindenotrithiophene (TITT) and Related π-Extended Oligoaryls

Truxenes, the π-conjugated small molecules with a C_3h-symmetry, have been extensively investigated in synthesis and application as organic optoelectronic materials. Compared to truxenes, triindenotrithiophene (TITT), a thienyl congener of truxene, was much less explored in the field of synthetic chemistry as well as photovoltaic applications. Different from the reported synthesis requiring at least 14 steps to access TITT-related small molecules, in this work, we have successfully developed a seven-step new synthetic route to TITT and its π-extended oligoaryls (YCW01-04). Our synthetic strategy involved two direct C─H/C─Br coupling reactions, avoiding tedious protection/deprotection chemical transformations. Essential reaction conditions including ligand, base, and solvent for direct C─H arylations were well-optimized, thus affording target products in yields up to 87% (YCW02). In addition, for the first time, the TITT core-based oligoaryls were fabricated as hole-transporting material (HTM) in perovskite solar cells (PSC), giving the highest power conversion efficiency (PCE) of 15.3% (YCW01).