Experimental and computational thermodynamics of pyrene and 1-pyrenecarboxaldehyde and their photophysical properties

A combined experimental and computational study was performed to evaluate the energetics, stability and volatility of pyrene and 1-pyrenecarboxaldehyde. The standard (p(o) = 0.1 MPa) molar enthalpy of combustion, Delta H-c(m)o, of 1-pyrenecarboxaldehyde was measured by static bomb combustion calorimetry, from which its standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived. The vapour pressures of the two compounds were measured at different temperatures using the Knudsen mass-loss effusion method enabling the determination of molar standard enthalpies and entropies of sublimation at the mean temperatures of the experiments and at 298.15 K, using estimated values of Delta C-g(cr)p,m(o) for the temperature adjustments. The temperature and the molar enthalpy of fusion of both compounds were determined using differential scanning calorimetry. From fluorescence spectroscopy measurements, their photophysical properties, in solution and in the solid state, were determined. The experimental thermodynamic and luminescence results were compared with values available in the literature. Additionally, standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed and the standard enthalpies of formation of these two compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Furthermore, the results were interpreted in terms of enthalpic increments. The gas-phase molar heat capacities and absolute entropies of the two compounds studied were also calculated. (C) 2015 Elsevier Ltd. All rights reserved.