The synthesis and characterisation of a homologous series of quinoid sulfur-containing imidazolyl-substituted heteroacenes is described. The optoelectronic and magnetic properties were investigated by UV/vis, fluorescence and EPR spectroscopy as well as quantum-chemical calculations, and were compared to those of the corresponding benzo congener. The room-temperature and atmospherically stable quinoids display strong absorption in the NIR region between 678 and 819 nm. The dithieno[3,2-b:2',3'-d]thiophene and the thieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophenederivatives were EPR active at room temperature. For the latter, variable-temperature EPR spectroscopy revealed the presence of a thermally accessible triplet state, with a singlet-triplet separation of 14.1 kJ mol À 1 .

The synthesis of three novel imidazolyl‐substituted sulfur‐containing heteroacenes is reported. These heteroacenes consisting of annelated benzo‐ and naphthothiophenes serve as precursors for the generation of open‐shell quinoid heteroacenes by oxidation with alkaline ferric cyanide. Spectroscopic and computational experiments support the formation of reactive open‐shell quinoids, which, however, quickly produce paramagnetic polymeric material.

The cover feature picture shows the successive expansion of a quinoid imidazolylidene‐substituted central sulfur‐containing heterocyclic core, which is accompanied by a continuous decrease in the HOMO/LUMO gap. This ultimately results in bench‐stable, open‐shell diradicals, as evidenced by the small singlet‐triplet gap. More information can be found in the Research Article by J. Paradies et al. (DOI: 10.1002/chem.202200478).