n-Type Conjugated Polymers Based on an Indandione-Terminated Quinoidal Building Block

Conjugated polymers (CPs) with deep LUMO energy levels (ELUMOs) are essential for developing n-type organic electronics. However, few approaches can markedly lower the ELUMOs of CPs. Herein, this issue is addressed by the introduction of a quinoidal building block into the polymer chain. Two CPs, PIQ-A and PIQ-O, are synthesized based on an indandione-terminated quinoidal unit, with alkyl or oligo(ethylene glycol) side chains on the comonomer, respectively. The CPs show ultralow ELUMOs of ca. -4.30 eV, which is lower by 0.75 eV compared to the analogous polymer with aromatic conjugated structure. The deep LUMO energy levels endow the CPs with unipolar n-type transport behavior in organic thin-film transistors and efficient n-type doping in organic thermoelectrics, with doped PIQ-O showing an optimized electrical conductivity of 0.43 S cm(-1) and a power factor of 4.24 mu W m(-1) K-2. Importantly, the electrical conductivity of doped polymer thin films (similar to 50 nm) barely changes after a 7 day exposure to air, and the doped PIQ-O film shows an electrical conductivity of 0.39 S cm(-1) even after a 15 day exposure to air. This work provides a new approach to develop CPs with ultralow LUMO energy levels, toward high-performance and potentially air -stable n-type organic electronics.