RESUMO
The kinetic and structural behavior of a photochromic compound, 3-(2-fluorophenyl)-3-phenyl-3H-naphtho[2,1-b]pyran (F-Py), was investigated using 1H and 19F nuclear magnetic resonance (NMR) spectroscopy. Upon irradiation, the four theoretically predicted photomerocyanines appear along with a fifth form X, whose final structure has not been elucidated. This last form and two of the photomerocyanines are thermally labile, whereas the other two do not show any signs of decay. The system has been analyzed by NMR spectroscopy. This led to the structural assignment of each photomerocyanine. The kinetics of the thermal bleaching were monitored by directly and separately measuring the concentrations of each species at regular time intervals using 19F NMR spectroscopy. We therefore propose a plausible reaction mechanism. On the basis of this mechanism, the mathematical treatment and the study of the effects of temperature led to the determination of the kinetic and thermodynamic parameters (rate coefficients, enthalpy and entropy of activation) of this photochromic system. The leading role of the labile intermediate X on the formation of trans-transoid-cis (TTC) and cis-transoid-cis (CTC) photomerocyanines is pointed out.
Assuntos
Carbocianinas/química , Naftalenos/química , Fármacos Fotossensibilizantes/química , Piranos/química , Pirimidinonas/química , Cinética , Espectroscopia de Ressonância Magnética/métodos , Modelos Moleculares , Estrutura MolecularRESUMO
The synthesis and characterisation of a new spin trapping agent of the spiro[indoline-naphthoxazinic] family is reported. The EPR results of spin trapping experiments are also described, which indicate the ability of this nitrone to react with carbon-, oxygen- and sulphur-centered radicals.
