High-pressure polymorphism of the electrochemically active organic molecule tetrahydroxy-p-benzoquinone

The structural and chemical response of tetrahydroxy-p-benzoquinone to isothermal compression to near 20 GPa have been studied using powder x-ray diffraction and vibrational spectroscopy. Compression beyond 11.5 GPa resulted in the appearance of several new peaks in the x-ray patterns, changes in the peak distribution and intensities, as well as the disappearance of features observed at lower pressures, which when coupled with concomitant changes in the infrared spectrum are indicative of a phase transition. Further analysis of the infrared spectra suggest this phase transition results in an increase in the anharmonicity of the system. Raman spectroscopic experiments indicate the high-pressure phase to be highly photosensitive and easily polymerized.