Alternating copolymers of oligoarylenes and naphthalene bisimides as low band gap semiconductors: Synthesis, electrochemical and spectroelectrochemical behavior

Three novel electroactive copolymers, consisting of alternating naphthalene bisimide and oligoarylene segments have been synthesized and studied by cyclic voltammetry and UV–vis-NIR spectroelectrochemistry. These studies show that the conjugation between both copolymer segments is very weak and the reduction of the bisimide part is essentially uninfluenced by the oligoarylene segment. The oxidation of the oligoarylene segment strongly depends on its length but is not affected by the presence of the bisimide part. The HOMO levels, determined electrochemically are systematically below −5.0 eV with respect to the vacuum level, changing from −5.45 eV for poly[1,4-phenylene-(4,3′(4′),3″-trioctyl-2,2′,5′,2″-terthiophene-5,5″-diyl)-1,4-phenylene-1,4,5,8-naphthalenediimide-N,N′-diyl] (6) to −5.50 eV in poly[1,4-phenylene-(4,4′-dioctyl-2,2′-bithiophene-5,5′-diyl)-1,4-phenylene-1,4,5,8-naphthalenediimide-N,N′-diyl] (5) and −5.84 eV for poly[1,4-phenylene-(3,4-dioctylthiophene-2,5-diyl)-1,4-phenylene-1,4,5,8-naphthalenediimide-N,N′-diyl] (4). The LUMO levels in all three cases are close to −4.0 eV. The obtained results clearly indicate that 5 and 6 are good candidates for the fabrication of ambipolar transistors operating in air whereas 4 can be considered as an active component of n-channels FETs.

► Donor-acceptor copolymers were prepared.
► Naphthalene bisimide core is acceptor unit.
► Oligothiophenes are donor units.
► Band gap can be tuned by adjusting length of donor part.
► Spectroelectrochemistry proves tuning of the band gaps.