Bridged 1,6-dithienylhexa-1,3,5-trienes as highly photoluminescent and stable thiophene-based π-conjugated systems

Bi- and tricyclic bridged dithienyl-1,3,5-hexatrienes (2 and 3) have been synthesized by McMurry dimerization of fused multicyclic ketones. The experimental conditions for the preparation of the precursor ketones have been established through a detailed analysis of the Robinson annulation of cyclopenta[b]thiophen-6-ones. The structures and electrochemical and optical properties of compounds 2 and 3 have been investigated using the open-chain analogue 1 as a reference. Whereas X-ray data confirm the highly conjugated and rigid structure of the bridged compounds, cyclic voltammetry and W-vis and photoluminescence spectroscopy show that rigidification of the pi-conjugated system produces a significant decrease in oxidation potential and HOMO-LUMO gap and a considerable enhancement of the photoluminescence quantum yield and thermal, stability.