Synthesis and Electronic Properties of Conjugated syn,syn-Dithienothiazine Donor-Acceptor-Donor Dumbbells

Abstract

A series of conjugated syn,syn-dithienothiazine donor-acceptor-donor dumbbells is readily synthesized by Suzuki coupling or a one-pot α-lithiation-zincation-Negishi coupling sequence in moderate to good yield. The title compounds are all electron-rich reversible oxidizable redox systems with a relatively narrow range of oxidation potentials according to cyclic voltammetry. UV/Vis and fluorescence spectroscopy however show a significant effect of the electronic nature of the conjugated bridging system on absorption and emission characteristics. Furthermore, a highly polar excited state can be corroborated by Lippert-Mataga analysis of the emission solvatochromicity as well as by TD-DFT calculation of absorption and emission maxima, which classify these dumbbell systems as redox active, luminescent low band gap chromophores with experimentally determined optical band gaps between 2.20 and 2.50 eV.