Fused hexacyclic thienoquinoids terminated by indandione for low bandgap organic semiconductors

Abstract

Two indandione-terminated quinoidal compounds, Q4T and Q4T-4F, featuring a fused-ring thiophene-thieno[3,2-b]thiophene-thiophene (4T) as the central core, were designed and synthesized. The extended π-conjugation of the 4T unit, combined with the quinoidal framework, significantly broadens the absorption spectrum, achieving a low-energy onset of up to 1107 nm. Despite their extended π-conjugation, both Q4T and Q4T-4F exhibit good stability in air, even under UV irradiation. In organic thin-film transistors, both compounds demonstrate electron-transporting behavior, with electron mobilities of (6.3 ± 0.8) × 10⁻⁴ and (1.2 ± 0.3) × 10⁻² cm² V⁻¹ s⁻¹ for Q4T and Q4T-4F, respectively. Notably, Q4T-4F exhibits higher electron mobility than Q4T, which is mainly attributed to its closer three-dimensional molecular stacking, as revealed by single-crystal analysis. This unique packing facilitates more efficient electron hopping between molecules. These findings provide an effective strategy for designing and synthesizing low-bandgap n-type molecules with good stability.