Thieno[3,2-b]thiophene−diketopyrrolopyrrole derivatives: Revised and scalable synthesis, optical and electronic properties

Thieno[3,2- b ]thiophene-based diketopyrrolopyrrole (DPP) derivatives are highly promising building blocks for low-bandgap organic semiconductors, yet their dialdehyde counterparts remain underexplored due to limited synthetic accessibility. Herein, we report an optimized and scalable synthesis of the thieno[3,2- b ]thiophene DPP dialdehyde, featuring an efficient one-pot introduction of a nitrile functionality and enabling multigram-scale production. This key intermediate was subsequently employed to prepare a series of π-conjugated small molecules of A–D–A–D–A structure via a straightforward Knoevenagel condensation with various acceptor units, thus avoiding the use of organometallic cross-coupling reactions. The resulting materials exhibit broad optical absorption and low bandgaps, with electrochemical and optical bandgaps in the ranges of 1.05–1.50 eV and 1.43–1.62 eV, respectively. The tetranitrofluorene DPP derivative synthesized displays the lowest electronic bandgap (1.05 eV), highlighting the effectiveness of conjugation extension of this π-conjugated system. Experimental results are in good agreement with time-dependent density functional theory calculations, with the HSE06 functional providing the most accurate description of frontier orbital energies. When evaluated in organic field-effect transistors, the materials show n -type behavior, with the tetracyano DPP derivative exhibiting the highest electron mobility, reaching (2.8 ± 0.4) × 10⁻³ cm²·V⁻¹·s⁻¹ after thermal annealing. Overall, this work demonstrates that thieno[3,2- b ]thiophene DPP dialdehyde is a versatile and synthetically accessible platform for the development of low-bandgap organic semiconductors via a metal-free strategy, opening new possibilities for scalable and high-performance electronic materials.