Rigid Fluorescent Indacenetetraone‐Based Semiconducting Polymers via Knoevenagel Condensation

Abstract The synthesis of new donor‐acceptor polymers is reported through Knoevenagel condensation of indacenetetraone with aromatic dialdehydes. The obtained polymers possess exceptionally rigid planar backbones with a rotational barrier (for single C─C bonds) of 16–20 kcal mol −1 , the highest among known conjugated polymers. These structural features confer several unusual properties, including remarkably narrow absorption bands with very high absorption coefficient (up to ≈3×10 5 cm −1 ) and efficient fluorescence in the red to near‐IR region (λ max 694–850 nm, quantum yield 10–29%). Systematic spectroscopic, electrical, and microstructural characterization supported by Density Functional Theory (DFT) calculations reveals the effects of heteroatoms and the conjugation lengths on the optoelectronic properties of these materials. The polymers exhibit ambipolar charge transport in field‐effect transistors, which can be tailored to show unipolar p ‐type (0.1 cm 2 V −1 s −1 ) and n ‐type (0.05 cm 2 V −1 s −1 ) behavior by adjusting the energy levels at the polymer/metal contacts. Additionally, their application is demonstrated as acceptors in all‐polymer organic photovoltaic devices with commercial donor polymers, achieving a power conversion efficiency (PCE) of 11%.