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 UV−vis and photoluminescence spectroscopy show that rigidification of the π-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.