Dibenzo[de,mn]naphthacene or zethrene is an aromatic hydrocarbon consisting of two phenalene units fused together. According to Clar's rule the two exterior naphthalene units are truly aromatic and the two central double bonds are not aromatic at all. For this reason the compound is of some interest to academic research. Zethrene is air and light sensitive (complete decomposition under a sunlight lamp within 12 hours) with a deep-red color. The melting point is 262 °C.
X-ray crystallography indicates that zethrene is a planar molecule. The bond lengths in the central part of the molecule are consistent with distinct single and double bonds rather than aromatic components.
^Kemp, William; Storie, Iain T.; Tulloch, Charles D. (1980). "Synthesis of potentially basic hydrocarbons by sulphur extrusion and/or bis-Wittig reactions. Two syntheses of benz[5,6]indeno[2,1-a]phenalene and a new synthesis of dibenzo[de,mn]naphthacene (zethrene)". Journal of the Chemical Society, Perkin Transactions 1: 2812. doi:10.1039/P19800002812.