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Dynamic vapor microextraction (DVME) is a new method that enables rapid vapor pressure measurements on large molecules with state-of-the-art measurement uncertainty for vapor pressures near 1 Pa. Four key features of DVME that allow for the rapid collection of vapor samples under thermodynamic conditions are (1) the use of a miniature vaporequilibration vessel (the "saturator") to minimize the temperature gradients and internal volume, (2) the use of a capillary vapor trap to minimize the internal volume, (3) the use of helium carrier gas to minimize nonideal mixture behavior, and (4) the direct measurement of pressure inside the saturator to accurately account for overpressure caused by viscous flow. The performance of DVME was validated with vapor pressure measurements of n-eicosane (C 20 H 42 ) at temperatures from 344 to 374 K. A thorough uncertainty analysis indicated a relative standard uncertainty of 2.03−2.82% for measurements in this temperature range. The measurements were compared to a reference correlation for the vapor pressures of n-alkanes; the deviation of the measurements from the correlation was ≤2.85%. The enthalpy of vaporization of n-eicosane at 359.0 K was calculated to be Δ vap H = 91.27 ± 0.28 kJ/mol compared to Δ vap H(corr) = 91.44 kJ/mol for the reference correlation. Total measurement periods as short as 15 min (3 min of thermal equilibration plus 12 min of carrier gas flow) were shown to be sufficient for high-quality vapor pressure measurements at 364 K.

Intramolecular photoinduced electron transfer from an N,N-dimethyl-p-phenylenediamine donor bridged by a diproline spacer to a coumarin 343 acceptor was studied using time-resolved fluorescence measurements in three ionic liquids and in acetonitrile. The three ionic liquids have the bis[(trifluoromethyl)sulfonyl]amide anion paired with the tributylmethylammonium, 1-butyl-1-methylpyrrolidinium, and 1-decyl-1-methylpyrrolidinium cations. The dynamics in the two-proline donor-bridge-acceptor complex are compared to those observed for the same donor and acceptor connected by a single proline bridge, studied previously by Lee et al. (J. Phys. Chem. C 2012, 116, 5197). The increased conformational freedom afforded by the second bridging proline resulted in multiple energetically accessible conformations. The multiple conformations have significant variations in donor-acceptor electronic coupling, leading to dynamics that include both adiabatic and nonadiabatic contributions. In common with the single-proline bridged complex, the intramolecular electron transfer in the two-proline system was found to be in the Marcus inverted regime.

The development of surrogate fuels with measured and predicted thermophysical properties similar to their authentic refinery stream counterparts is critical for the development of alternative fuels and the optimization of engines to increase efficiency and decrease emissions. In this work, four diesel fuel surrogates, formulated according to a reliable and proven procedure, were characterized by the advanced distillation curve (ADC) method to determine the composition and enthalpy of combustion in various distillate volume fractions. Tracking the composition and enthalpy of distillate fractions provides valuable information for determining structure–property relationships and also provides the basis for the development of equations of state that can describe the thermodynamic properties of these complex or simplified mixtures. This comparison showed that the volatility characteristic of the four surrogates is quite similar not only to the target diesel fuel but also to a number of other prototype alternative diesel fuels. The number of components in the surrogates affected how closely their volatility profiles resembled diesel fuel, as might be expected. The surrogate labeled V0a, consisting of just four components, was the most dissimilar to the target diesel fuel with respect to the initial boiling point and volatility curve shape. This suggests that, although minimizing the number of components greatly eases modeling and formulation efforts, caution should be used to avoid oversimplifying the surrogate mixtures.

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