Phase transition thermodynamics of organic semiconductors N,N,N′,N′-tetraphenyl-p-phenylenediamine, N,N′-diphenyl-N,N′-di-p-tolylbenzene-1,4-diamine, and 4,4′-bis(m-tolylphenylamino)biphenyl

Abstract

In this paper, we report a comprehensive analysis of the thermodynamic properties of organic semiconductors, namely, N,N,N′,N′-tetraphenyl-p-phenylenediamine (DDP), N,N′-diphenyl-N,N′-di-p-tolylbenzene-1,4-diamine (p-TTP), and 4,4′-bis(m-tolylphenylamino) biphenyl (TPD). Vapor pressures above crystalline and liquid (including supercooled liquid) phases over a wide temperature range were measured using thermogravimetry-fast scanning calorimetry method (TG- FSC). Based on the vapor pressures, the vaporization and sublimation enthalpies of the studied compounds were derived. Heat capacities of condensed phases, melting points and fusion enthalpies of DDP, p-TTP, and TPD were measured by differential scanning calorimetry. Using the measured heat capacities of the liquid and crystalline phases and the computed heat capacities of the ideal gas phase, the experimental data obtained in the present work were adjusted to 298.15 K and compared with the available literature values. For additional verification of the obtained results, the solution calorimetry method was applied, providing an independent way to determine fusion enthalpies at 298.15 K. The obtained data can be used for optimization of the vacuum deposition processes and determination of thermodynamic properties of glasses.