Benzo[b]thiophene-Fused Boron and Silicon Ladder Acenes

Synthetic routes to three new heteroacene compounds in which two benzo­[b]­thienyl units are bridged by dimethylsilyl and/or mesitylboryl units are described. In the Si/Si and Si/B compounds 1-syn and 3-syn, respectively, the sulfur atoms of the flanking benzo­[b]­thiophenes are disposed in meta positions on the central six-membered heterocycle, while in the B/B compound 4-anti, they are para to each other; the reasons for this lie in the synthetic method employed to prepare 4-anti. All three compounds were crystallographically characterized and their photophysical properties examined. A comprehensive examination of their photophysical properties shows that they are weakly absorbing and fluorescing materials, with the diborin derivative 4-anti exhibiting the most red-shifted absorption maxima and largest fluorescence quantum yield.