Conjugated Ladder Polymers by a Cyclopentannulation Polymerization

We report a nontraditional synthesis of cyclopentafused-polycyclic aromatic hydrocarbon embedded ladder polymers using a palladium catalyzed cyclopentannulation polymerization followed by a cyclodehydrogenation reaction. Donor-acceptor type polymers containing a cyclopenta[hi]aceanthrylene acceptor groups can be synthesized by a palladium catalyzed copolymerization between 9,10-dibromoanthracene and a variety of bis(arylethynyl)arenes to give polymers with molecular weights (Mn) of 9-22 kDa. The bis(arylethynyl)arenes were composed of benzene, thiophene, or thieno[3,2-b]thiophene moieties, which provided access to a series of four donor-acceptor copolymers. The polymers were subjected to cyclodehydrogenation with FeCl₃ to access rigid ladder type polymers with the conversion investigated by ¹³C NMR of isotopically labeled polymers. The ladder polymers possess broad UV-Vis absorptions and narrow optical band gaps of 1.17-1.29 eV and are p-type semiconductors in organic field effect transistors.