Synthesis and Characterization of Thiophene‐Endcapped 3,7‐Diphenyl Dipyrrolo[2,3‐b : 2′,3′‐e]pyrazine‐2,6(1H,5H)‐diones as Non‐Fullerene Acceptor Materials for Organic Solar Cells

Four conjugated small molecules (2TPzDP, 3TPzDP, 2TTPzDP, and 3TTPzDP) were synthesized consisting of a 3,7‐diphenyldipyrrolo[2,3‐b : 2′,3′‐e]pyrazine‐2,6(1H,5H)‐dione core end‐capped with either 2‐alkylthiophene (2T), 3‐alkylthiophene (3T), 2‐alkyl‐2,2′‐bithiophene (2TT) or 3‐alkyl‐2,2′‐bithiophene (3TT). All the compounds exhibited two absorption bands, one in the ultraviolet (λmax=307–347 nm) and other in the visible (λmax=582–631 nm) region. The HOMO/LUMO values for 2TPzDP, 3TPzDP, 2TTPzDP, and 3TTPzPDP were measured as −5.68/−3.97, −5.67/−3.97, −5.49/−4.01, and −5.45/−3.99 eV, respectively, which are well matched with regioregular poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) (−5.0/−3.0 eV) to act as n‐type semiconductors for photovoltaic applications. Fluorescence quenching experiments revealed an efficient charge transfer between the donor material P3HT and the synthesized acceptor molecules. The Td values of all the four compounds are in the range of 355–391 °C representing their good thermal stability. These properties evaluated are found to be excellent for the fabrication of bulk heterojunction organic solar cells using P3HT. Conjugation: Four new thiophene‐endcapped 3,7‐diphenyldipyrrolo[2,3‐b : 2′,3′‐e]pyrazine‐2,6(1H,5H)‐diones 2TPzDP, 3TPzDP, 2TTPzDP, and 3TTPzDP with PzDP as the core building block and alkylthiophene or alkyl‐2,2′‐bithiophene moieties as end capping units are synthesized. The good optical properties, suitable HOMO/LUMO energy levels, and excellent Td values portray them as good candidates as small molecule non‐fullerene acceptors for the realization of highly efficient BHJOSCs.