Thienyl naphthodipyrrolopyrrole (TNDP)-based polymers semiconductor for n-type OFETs

Abstract

Naphthodipyrrolopyrrole (NDP)-based materials as the n-type semiconductor materials are investigated, which present a good electron transport mobility. However, all the reported NDP were phenyl-substituted ones (PhNDP). Compared to the phenyl substituted chromophore, the thiophene substituted ones were often more promising due to its small size, S⋯S interaction, as well as the electron-rich behavior for the thiophene. Thus, in this work the new chromophore thiophene-substituted NDP (TNDP) was designed and synthesized for the first time via Knoevenagel reaction. In addition, two donor-acceptor typed copolymers PNDP-2T and PNDP-IDT containing TNDP were prepared. The result showed that the two polymers present not only a good aggregation and strong intramolecular charge transfer (ICT) effect, but also a low lowest unoccupied molecular orbital (LUMO) ∼ -4.17 eV. This is advantageous for the charge transport within the single molecules as well as across the neighboring polymer chains. In addition, the low LUMO energy level is beneficial for the electron injection from electrode into the semiconductor layer. As a consequence, both polymers presented n-type behavior. The electron transport mobility of PNDP-IDT was up to 0.99 cm2 V−1 s−1, which is among the highest electron mobility reported for conjugated polymers. In addition, this value is higher than the PNDP-based polymers with similar chemical structure. This work clearly shows that TNDP is an appealing electron-deficient building block for novel π-conjugated polymers with application potential in the n-channel semiconductors.