Triphenylene

"In chemistry, the organic compound triphenylene is a flat polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings. Triphenylene can be isolated from coal tar, but it is also made synthetically using benzyn chemistry. One molecule of triphenylene has delocalized 18-π-electron systems based on a planar structure. It has the molecular formula C₁₈H₁₂."

"Triphenylene is a fully benzenoid PAH, meaning its structure is composed only of full benzene rings interconnected by carbon-carbon single bonds. The three benzene rings can be drawn as the three outer rings, with the central ring formed by one face of each and the three carbon-carbon single bonds."

"Being a fully bezenoid PAH means that triphenylene is much more resonance stable than its isomers chrysene, benz[a]anthracene, benzo[c]phenanthrene, andtetracene. This makes it much more difficult to hydrogenate to the saturated hydrocarbon."