Thermal back-isomerization of spirocyclic naphtho-oxazine and phenanthro-oxazine derivatives in alcohols, nitriles, and poly(alkyl methacrylates)
The thermal back-isomerization of spiro[indole-naphtho-oxazine] 1 and spiro[indole-phenanthro-oxazine] 2 was studied in a series of primary alcohols, nitriles, and poly(methylmethacrylate), poly(ethylmethacrylate), and poly(isobutyl methacrylate) films by laser-flash photolysis in the temperature ra...
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2001
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0018019X_v84_n9_p2751_Volker http://hdl.handle.net/20.500.12110/paper_0018019X_v84_n9_p2751_Volker |
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| Sumario: | The thermal back-isomerization of spiro[indole-naphtho-oxazine] 1 and spiro[indole-phenanthro-oxazine] 2 was studied in a series of primary alcohols, nitriles, and poly(methylmethacrylate), poly(ethylmethacrylate), and poly(isobutyl methacrylate) films by laser-flash photolysis in the temperature range of 0-70°. The decay is monoexponential in fluid solution, but deviates strongly from this behavior in polymeric environments even above the glass transition temperature of the polymers (Tg). In liquids, a very small solvent effect is observed on the isomerization rate constants (kiso) for 1, which is attributed mostly to the solvent viscosity η. The values of kiso for 2 show influence of solvent viscosity and polarity, which were studied by application of a semiempirical relationship that accounts for non-Markovian processes. The decay kinetics in polymers was described by a Gaussian distribution of the activation energy and by a kinetic model that takes into account the simultaneous relaxation of the probe and the environment. For 1 and 2, the rate constant at the center of the Gaussian distribution is very similar to the first-order rate constant in nonpolar solvents. The Gaussian width of the distribution (σ) decreases with temperature and is very similar in all polymers under Tg, and, above Tg, σ decreases more abruptly. We make comparisons of the parameters derived from analysis of both 1 and 2 in polymers, as well as of their behaviors in solution and in polymers. |
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