Monodisperse macromolecules based on benzodithiophene and diketopyrrolopyrrole with strong NIR absorption and high mobility

A series of monodisperse macromolecules with A₂–A₁–D–A₁–A₂ structure based on benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) BDT-4DPP, BDT-DPP-Rhod and BDT-DPP-CA were designed, theoretically calculated and synthesized, and compared with their parent molecules BDT-2DPP and BDTS-2DPP with A₁–D–A₁ structure. These molecules possessed highly planar molecular geometries and high crystallinity. These molecules exhibited good thermal stability with decomposition temperatures of 322–388 °C, strong visible and near-infrared absorption (500–1000 nm), and HOMO energy levels of −5.38 to −5.19 eV and LUMO energy levels of −3.69 to −3.46 eV. Relative to the parent molecules A₁–D–A₁, A₂–A₁–D–A₁–A₂ molecules exhibited red-shifted and stronger absorption. The charge transport properties of these molecules were investigated by organic field-effect transistors, and their hole mobilities were 0.036–1.12 cm⁻² V⁻¹ s⁻¹. Replacing alkyl with alkylthio on BDT led to mobility enhancement by one order of magnitude.