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- Title
Thermal Back-Isomerization of Spirocyclic Naphtho-oxazine and Phenanthro-oxazine Derivatives in Alcohols, Nitriles, and Poly(alkyl methacrylates).
- Authors
Völker, Edgar; O'Connell, Manuela; Negri, R. Martín; Aramendía, Pedro F.
- Abstract
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.
- Publication
Helvetica Chimica Acta, 2001, Vol 84, Issue 9, p2751
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/1522-2675(20010919)84:9<2751::AID-HLCA2751>3.0.CO;2-H