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The thermodynamic properties and band gap energies were evaluated for six ortho- and peri-fused polycyclic aromatic hydrocarbons (PAHs): triphenylene; benzo[a]pyrene; benzo[e]pyrene; perylene; benz...

The molecular and supramolecular structure and energetics of tetracene and rubrene were investigated by a combined experimental and theoretical study. Accurate equilibrium vapour pressures at various temperatures were measured for both compounds. For rubrene the energetic analysis evidences lower crystal packing efficiency, strong molecular destabilization and confirms the non-planar twisted equilibrium structure in the gas phase. The results also indicate that phenyl internal rotation in rubrene is highly hindered. The intra- and intermolecular interactions in crystal tetracene and rubrene were evaluated by computational methods. The representative stacked dimer of the tetracene...tetracene interaction in rubrene has lower ionization energy than the one modelling the same interaction in tetracene, due to stronger cation...pi interactions in the cation-radical of rubrene. Charge distribution in the cation dimer is symmetrical in rubrene, whereas in tetracene it is largely localized on the C-H center dot center dot center dot pi donor partner of the herringbone dimer. These findings highlight the impact of cation...pi interactions on the semiconducting properties of OSCs.

A new Knudsen effusion apparatus, enabling simultaneous gravimetric and quartz crystal microbalance mass loss detection, is described. This device allows the measurement of vapour pressures of small sample mass (50 to 100) mg over a wide temperature range (350 to 650) K using very short effusion time intervals. The performance of the apparatus was checked by measuring the vapour pressures of anthracene, benzanthrone, and 1,3,5-triphenylbenzene, between (0.1 and 1) Pa, over temperature intervals of 20 K. The derived standard molar enthalpies of sublimation and vapour pressures are in excellent agreement with the mean of the available literature values and with the recommended values. The new working methodology and design of this apparatus allows the measurement of high quality vapour pressure data due to: accurate temperature measurement and control; improvement in vacuum thermal contact between the effusion cell and the oven metal block; optimisation of the quartz crystal sensor head microbalance position; efficient temperature control of the quartz crystal microbalance head; accurate measurement of the resonance crystal frequency using an impedance circuit analyser methodology.

A new mini-bomb combustion calorimeter designed at the University of Lund was improved, installed and calibrated at the University of Porto. This calorimeter is suitable for high precision combustion calorimetry with samples of mass about (10 to 40) mg. The energy equivalent of the calorimeter, ecal = (1946.45 ± 0.11) J · K−1, was obtained from 15 independent calibration experiments with benzoic acid SRM 39i. Anthracene, succinic acid, acetanilide, and 1,2,4-triazole were used as test compounds, with excellent agreement with the literature values. - Δ c H m ∘ Δ f H m ∘ ( cr ) kJ · mol−1 kJ · mol−1 Anthracene 7062.6 ± 2.1 124.3 ± 2.8 Succinic acid 1490.2 ± 0.7 −941.3 ± 0.9 Acetanilide 4226.2 ± 1.1 −208.2 ± 1.6 1,2,4-Triazole 1326.1 ± 0.4 110.3 ± 0.5

The standard (po=0.1 MPa) molar enthalpies of formation for crystalline 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline were derived from the standard molar enthalpies of combustion, in oxygen, at the T=298.15 K, measured by rotating bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystals as function of temperature, and the standard molar enthalpies of sublimation, at T=298.15 K, were derived by the Clausius–Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation, using Calvet microcalorimetry, for 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline confirmed the values derived from the Knudsen technique. Δ f H m 0 (cr) Δ cr g H m 0 (kJ · mol−1) (kJ · mol−1) Calvet Knudsen 2-Chloro-4-nitroaniline (2-Cl-4-NO2-C6H3NH2) −74.9 ± 1.4 101.8 ± 1.8 102.6 ± 1.5 2-Chloro-5-nitroaniline (2-Cl-5-NO2-C6H3NH2) −71.0 ± 1.5 100.3 ± 2.2 101.0 ± 1.6 Additionally, standard enthalpies of formation were estimated by employing two different methodologies. One is based on the Cox scheme and the other one, much more accurate, is based on first-principles calculations. The theoretical calculations were performed at the AM1, B3LYP/6-31+G** and BP86/6-31+G** levels of theory. Estimated values are in good agreement with the reported experimental numbers.

The energetic study of 1,2,3-triphenylbenzene (1,2,3-TPhB) and 1,3,5-triphenylbenzene (1,3,5-TPhB) isomers was carried out by making use of the mini-bomb combustion calorimetry and Knudsen mass-loss effusion techniques. The mini-bomb combustion calorimetry technique was used to derive the standard (p° = 0.1 MPa) molar enthalpies of formation in the crystalline state from the measured standard molar energies of combustion for both isomers. The Knudsen mass-loss effusion technique was used to measure the dependence with the temperature of the vapour pressure of crystalline 1,2,3-TPhB, which allowed the derivation of the standard molar enthalpy of sublimation, by application of the Clausius–Clapeyron equation. The sublimation study of 1,3,5-TPhB had been performed previously. From the combination of data obtained by both techniques, the standard molar enthalpies of formation in the gaseous state, for both isomers, at T = 298.15 K, were calculated. The results indicate a higher stability of the 1,3,5-TPhB isomer relative to 1,2,3-TPhB, similarly to the terphenyls. Nevertheless, the 1,2,3-TPhB isomer is not as energetically destabilized as one might expect, supporting the existence of a π–π displacive stacking interaction between both pairs of outer phenyl rings. The volatility difference between the two isomers is ruled by the enthalpy of sublimation. The volatility of the 1,2,3-TPhB is two orders of magnitude higher than the 1,3,5-TPhB isomer, at T = 298.15 K. Δ c U m ∘ / ( kJ · mol - 1 ) Δ f H m ∘ ( g ) / ( kJ · mol - 1 ) 1,2,3-Triphenylbenzene (1,2,3-TPhB) −12248.2 ± 4.1 376.7 ± 5.3 1,3,5-Triphenylbenzene (1,3,5-TPhB) −12224.6 ± 3.6 366.8 ± 4.9