Heptacene is an organic compound and a polycyclic aromatic hydrocarbon and the seventh member of the acene or polyacene family of linear fused benzene rings.[1] This compound has long been pursued by chemists[2][3][4] because of its potential interest in electronic applications and was first synthesized but not cleanly isolated in 2006.[5][6] Heptacene was finally fully characterized in bulk by researchers in Germany and the United States in 2017.[7]
The final step is a photochemical decarbonylization with a 1,2-dione bridge extruded as carbon monoxide. In solution heptacene is not formed because it is very unstable being a reactive DA diene and quickly reacts with oxygen or forms dimers. When on the other hand the dione precursor is dissolved in a PMMA matrix first, heptacene can be studied by spectroscopy. Heptacene has been studied spectroscopically at cryogenic temperatures in a matrix.[8] When dissolved in sulfuric acid the heptacene dication is reported to be stable at room-temperature for more than a year in absence of oxygen.[9]
"[Isolated] solid heptacene has a half-life time of several weeks at room temperature."[10]
7,16-Bis(tris(trimethylsilyl)silylethynyl)heptacene was synthesized in 2005.[11] This compound is stable in the solid state for a week but decomposes in contact with air. Its synthesis started from anthraquinone and naphthalene-2,3-dicarboxaldehyde. More stable substituted heptacenes have been reported: with stabilizing p-(t-butyl)thiophenyl substituents (Figure 1)[12] and with phenyl and triisopropylsilylethynyl groups (Figure 2).[13]
