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(More) About biphenyl first excited triplet state energy
Gomes, Paulo J. S.; Serpa, Carlos; Arnaut, Luís G.Biphenyl photophysics was extensively studied in the past and much attention was given to the measurement of its first excited triplet state energy. Phosphorescence and the corresponding T1 <-- S0 absorption give triplet energies that differ by 10 kcal mol-1. We revisited biphenyl photophysics using photoacoustic calorimetry (PAC), a technique that directly measures the thermochemistry and kinetics of short...
1,3-Dipolar cycloaddition of azomethine ylides generated from aziridines in sup...
Gomes, Paulo J. S.; Nunes, Cláudio M.; Pais, Alberto A. C. C.; Melo, Teresa M. V. D. Pinho e; Arnaut, Luis G.The 1,3-dipolar cycloaddition of azomethine ylides with DMAD in supercritical carbon dioxide is reported. The photolysis reaction conditions were optimized with a suitable adjustment of pressure, temperature, irradiation time and co-solvent concentration leading to a more efficient reaction than in neat acetonitrile. Similar results were observed using thermal reaction conditions. Supercritical carbon dioxide w...
Temperature Dependence of Ultra-Exothermic Charge Recombinations13
Serpa, Carlos; Gomes, Paulo J. S.; Arnaut, Luis G.; Melo, J. Seixas de; Formosinho, Sebastião J.We measured the temperature dependence (from +32 to -50 °C) of charge-recombination rates between contact radical ion pairs in isopropyl ether. In the systems selected for this study, aromatic hydrocarbon cations are the electron acceptors and the fumaronitrile anion is the electron donor. Nearly quantitative electron transfers occur at all temperatures. The charge recombinations have excess exothermicities of ...
Electron Transfer in Supercritical Carbon Dioxide: Ultraexothermic Charge Recom...
Serpa, Carlos; Gomes, Paulo J. S.; Arnaut, Luis G.; Formosinho, Sebastião J.; Pina, João; Melo, J. Seixas deCharge-recombination rates in contact radical-ion pairs, formed between aromatic hydrocarbons and nitriles in supercritical CO2 and heptane, decrease with the exothermicity of the reactions until they reach -70 kcal mol-1, but from there on an increase is observed. The first decrease in rate is typical of the ldquoinverted regionrdquo of electron-transfer reactions. The change to an increase in the rate for ult...
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