Triphenylene

In chemistry, the organic compound triphenylene is a flat polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings. It is also known as benzo[l]phenanthrene, 9,10-benzophenanthrene, 1,2,3,4-dibenznaphthalene, and isochrysene. Triphenylene is isolated from coal tar. 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 chysene, benz[a]anthracene, benzo[c]phenanthrene and naphthacene (tetracene). This makes it much more difficult to hydrogenate to the saturated hydrocarbon.

From this characteristic, triphenylene is an attractive material for optical and electronic devices. Although consisting of colorless needle-like crystals, triphenylene emits bluish purple fluorescence by UV irradiation. Triphenylene is a disc-shaped molecule with a planar structure and three-fold rotation axes.

In terms of its crystallographic point group, the symmetry of triphenylene is classified as C3h in Schoenflies notation. Because of these characteristics, six-fold (in the 2, 3, 6, 7, 10, and 11 positions) alkyloxy- or alkylthiol-substituted triphenylenes can be used as a discotic mesogen in liquid crystalline materials.