The fusion thermochemistry of rubrene and 9,10-diphenylanthracene between 298 and 650 K: Fast scanning and solution calorimetry

The fusion enthalpies and the heat capacities of crystalline, molten, and supercooled liquid rubrene (Tm = 603 K) and 9,10-diphenylanthracene (Tm = 523 K) were measured using fast scanning calorimetry and conventional DSC. The experimental fusion enthalpies at the melting temperature were corrected to 298.15 K according to Kirchhoff’s law of thermochemistry. On the other hand, the fusion enthalpies at 298.15 K were determined from the solution enthalpies of these compounds in benzene, considering “like dissolves like” principle. The fusion enthalpies at 298.15 K obtained using independent methods were in mutual agreement. The heat capacity corrections of the fusion enthalpies of the studied non-planar polycyclic aromatic hydrocarbons to 298.15 K were found to be significantly higher than for planar polyaromatics. The features of measurement of the heat capacities of organic compounds by fast scanning calorimetry in the temperature range of notable volatility were discussed. The complete absence of the mass losses during heating-cooling cycles was found to be unnecessary condition for accurate heat capacity measurement; tolerable mass losses during the procedure were evaluated.