Solid solution of triptycenequinone and triptycenehydroquinone as a non-stoichiometric quinhydrone. Bathochromic changes in color caused by local intermolecular interaction between p-benzoquinone and hydroquinone moieties

Binary crystal formed by 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-dione (triptycenequinone, TPQ, yellow) and 9,10-dihydro-9,10-[o]benzenoanthracene-1,4-diol (triptycenehydroquinone, TPHQ, colorless) was found to be a substitutional solid solution of TPQ doped by TPHQ with concentration of TPHQp-benzoquinone and hydroquinone moieties of TPQ and TPHQ, respectively, enabled by a disorder in the binary crystal. It seemed appropriate to regard the solid solution as non-stoichiometric quinhydrone. Crystal structure of pure TPHQ is also reported. A common molecular arrangement in the crystals of pure TPQ and pure TPHQ, as well as the resemblance in the molecular structure, seems to be favorable for the formation of the solid solution.